OPHTHALMOLOGY

Care of the eye during anaesthesia and intensive care

Learning objectives After reading this article, you should be able to: C understand the different aetiology of the two major causes of postoperative blindness C identify patients at high risk of postoperative visual loss and take appropriate prevention strategies C understand the aetiology and effective prevention of perioperative corneal abrasions.

Emert White Don B David

Abstract Perioperative eye injuries and blindness are rare but important complications of anaesthesia. The three causes of postoperative blindness are ischaemic optic neuropathy, central retinal artery occlusion (these two causes can exist in tandem and have been described as ischaemic oculopathies), and corneal abrasion. This article aims to improve the readers’ knowledge of orbital anatomy, ocular physiology and the mechanisms of perioperative eye injuries.

vessels are distributed within the inner two-thirds of the retina, while the choroidal circulation supplies the outer layers of the retina. Two or three posterior ciliary arteries arise from the ophthalmic artery, each of which divides into one long posterior ciliary artery and between eight and ten short posterior ciliary arteries. The short posterior ciliary arteries pierce the sclera and form the choriocapillaris, which supplies the anterior part of the optic nerve, the lamina cribosa and the choroid posterior to the equator. The choriocapillaris is composed of small lobules supplied by a terminal arteriole. Each lobule has draining venules at the periphery. The long posterior ciliary arteries travel forward in the suprachoroidal space to the ciliary body where they combine with the anterior ciliary arteries to form the major arterial arcade. Recurrent branches of the long posterior ciliary arteries supply the choroid anterior to the equator and anastomose with the short posterior ciliary arteries. Age-related arteriosclerotic changes in the orbital arteries are more severe in the most proximal vessels, which is similar to the rest of the arterial tree. In particular, arteriosclerotic changes tend to be most marked where the ophthalmic artery enters the orbit and at the origins of the posterior ciliary arteries and central retinal artery.3 There is a significant reduction in blood flow through the ophthalmic artery with increasing age.4 Watershed zones are believed to occur between the:
choroidal and retinal circulation
long posterior ciliary arteries
short posterior ciliary arteries
long posterior ciliary arteries and the anterior ciliary arteries
choriocapillaris lobules. Hence in the event of ischaemia the pattern of visual disturbance is variable.

Keywords Central retinal artery occlusion; corneal abrasion; intraocular pressure; ischaemic optic neuropathy

Perioperative eye injuries and blindness are rare but important complications of anaesthesia. Eye injuries account for 2% of negligence claims against anaesthetists.1 The three main problems are ischaemic optic neuropathy, central retinal artery thrombosis, and corneal abrasion. A better understanding of orbital anatomy and ocular physiology, and the mechanisms of ocular injuries during anaesthesia may help to reduce their incidence.

Arterial supply to the optic nerve and retina The ophthalmic artery enters the orbit through the optic canal enclosed within the dural sheath of the optic nerve and its first branch within the orbit. The central retinal artery runs along the inferior aspect of the optic nerve, exiting from the dural sheath of the optic nerve approximately 10 mm behind the globe. The vascular supply to this posterior part of the optic nerve is from pial branches of the ophthalmic artery and the central retinal artery.2 The central retinal artery divides into four major vessels at the optic disc, each supplying one quadrant of the retina. The retinal

Ocular blood flow and perfusion Ocular blood flow (OBF) is determined by the pressure difference between mean arterial pressure (Pa) and mean venous pressure (Pv), and the resistance to that flow (R).

Emert White FRCA is Consultant Anaesthetist at Warwick Hospital, Warwick, UK. He qualified from the University of Birmingham and trained in anaesthesia in Nottingham and Southampton, UK, and Sydney, Australia, and Ann Arbor, USA. His research interest is ocular physiology. Conflicts of interest: none declared.

OBF ¼

Don B David FRCOphth is Consultant Ophthalmologist at Warwick Hospital, Warwick, UK. He qualified from the University of Alberta, Canada and trained in ophthalmology in Liverpool, Bristol and Birmingham, UK, and Brisbane, Australia. His research interest is oculoplastic surgery. Conflicts of interest: none declared.

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Pa  Pv R

Retinal blood flow is approximately 170 ml/100 g/minute. Choroidal blood flow is high (around 2000 ml/100 g/minute) and accounts for between 60 and 80% of the retinal oxygen supply. Blood flow to the temporal side of the retina is approximately three

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using The USA Nationwide Inpatient Sample (NIS) database of over 5.6 million patients was highest following cardiac surgery (8.6 per 10,000) and spinal surgery (3 per 10,000) falling to 0.12 per 10,000 after appendectomy.9 Patients younger than 18 years old had the highest risk of POVL because of a higher risk for cortical blindness, whereas patients greater than 50 years old had a greater risk of ION and CRAO. Overall the annual rate of POVL decreased over a 10-year period from 1996 to 2005. Ischaemic optic neuropathy is classified into either anterior ischaemic optic neuropathy (AION) or posterior ischaemic optic neuropathy (PION). AION is characterized by infarction at watershed zones (described above), a visual field defect, a pale oedematous optic disc, flame-shaped retinal haemorrhages, and oedema of the optic nerve in the posterior scleral foramen. PION occurs when the pial branches of the ophthalmic artery become occluded. Blood flow in the posterior part of the optic nerve is significantly less than that in the anterior part of the optic nerve. These pial vessels are end arteries that are not capable of autoregulatory control, and therefore this part of the optic nerve is more vulnerable to ischaemia in the event of a fall in perfusion pressure or anaemia.10 PION is characterized by a slower onset of visual field defect and mild optic-disc oedema. The incidence of ischaemic optic neuropathy varies between 1 in 30,000 and 60,000 operations. High-risk procedures are spinal surgery, cardiopulmonary bypass and bilateral neck dissection. The probable mechanism of ischaemic optic neuropathy following bilateral radical neck dissection is a reduction of perfusion pressure caused by an increase in venous pressure due to ligation of veins in the neck, and arterial hypotension. There are multiple reasons for postoperative visual loss after cardiac surgery: embolic, changes in oncotic pressure, ischaemic, thrombotic and surgical technique. The American Society of Anesthesiologists postoperative visual loss registry recently published its analysis of 93 cases of POVL after spinal surgery in the prone position.11 Ischaemic optic neuropathy occurred in 83 of the 93 patients. In 55 patients with ischaemic optic neuropathy, visual loss affected both eyes. The average duration of general anaesthesia for patients with ischaemic optic neuropathy was 9.8 hours, with a median blood loss of 2 litres. Of particular interest is that 70% of affected patients were male. Central retinal artery occlusion was the cause of unilateral visual loss in 10 patients (11%) in the registry. The average duration of general anaesthesia was 6.5 hours for these patients, with a median blood loss of 0.75 litres. Head rests (including horseshoe head rests) were used in all cases (in contrast to a 20% use of Mayfield pins ensuring the eyes were free of pressure in patients with ischaemic optic neuropathy). Stigmata of periocular trauma were present in 70% of patients with central retinal artery occlusion:
decreased supraorbital sensation
unilateral erythema
periorbital oedema
ptosis
chemosis
corneal abrasion
ophthalmoplegia
proptosis. These findings suggest that central retinal artery occlusion tends to follow globe compression in prone patients due to poor positioning of the patient’s head.

times larger than the nasal side. Retinal blood flow is affected by changes in the partial pressure of arterial oxygen (PaO2) and carbon dioxide (PaCO2), arterial blood pressure, and perfusion pressure. The choroidal circulation responds to changes in PaO2, PaCO2 and arterial blood pressure, but not to increases in intraocular pressure (i.e. perfusion pressure). Inhalation of 100% oxygen causes retinal vasoconstriction, which reduces retinal blood flow by 60%. However, this reduction is not sufficient to prevent an overall increase in retinal pressure of oxygen (PO2). Inhalation of carbon dioxide causes retinal vasodilatation. Retinal blood flow increases by 3% for each 1 mmHg increase in PaCO2. In most patients a stable retinal blood flow is maintained by autoregulation, over a wide range of perfusion pressures. However, in a significant proportion of patients (around 20%) autoregulation fails to occur, which results in a progressive reduction in retinal blood flow at the onset of an increase in intraocular pressure or hypotension. As a result of the lack of choroidal autoregulation during increases in intraocular pressure, the PO2 in the choroid and outer retina decreases. In primates irreversible damage occurs if ocular ischaemia exceeds 100 minutes, but in humans there is little correlation between occlusion time and visual outcome. In the upright position the pressure within the artery entering the eye is 60e70 mmHg, while the intraocular pressure is 10e15 mmHg, which under normal conditions provides a perfusion pressure of approximately 50 mmHg. The episcleral venous pressure is approximately 3e7 mmHg (7e8 mmHg lower than the intraocular pressure), and increases by 3e4 mmHg in the supine position. If large increases in episcleral venous pressure occur, part of this pressure will be transmitted into the intraocular veins causing congestion, with reduced perfusion pressure. An increase in volume of the intraocular vascular bed of 1e4 ml will increase the intraocular pressure by 1e2 mmHg. Intraocular pressure varies (IOP) with posture.5 Clinically significant increases have been observed in both awake and anaesthetized patients positioned prone. There have been two studies of the effect of the prone position in anaesthetized patients.6,7 Both studies found that the IOP increased markedly when the patient was turned prone, and that there was a tendency for increasing IOP with time. A further study in awake volunteers positioned prone showed significant increases in IOP, choroidal layer thickness and optic nerve diameter over 5 hours all of which returned to normal values within 30 minutes after being returned to the supine position.8 The implications of these studies are that the prone position causes increased intraorbital venous pressure and hence reduced ocular perfusion pressure. Optic nerve ischaemia The causes of optic nerve ischaemia are listed below:
arterial hypotension (hypotensive anaesthesia, haemorrhage)
elevated venous or intraocular pressure (prone position)
increased resistance to flow (atherosclerosis, diabetes mellitus, hypertension, cigarette smoking, polycythaemia)
decreased oxygen delivery (anaemia).

Postoperative visual loss There are two main causes of postoperative visual loss (POVL): ischaemic optic neuropathy (ION) and central retinal artery occlusion (CRAO). Cortical blindness due to ischaemia of the occipital cortex is a rare cause of POVL. The prevalence of POVL

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Methods of eye protection during general anaesthesia Method Manual closure of the eyelids

Advantages C Avoids trauma to the eye and eyelids C Avoids chemical injuries associated with tapes, gels and ointments

Taping the eyelids closed

C

Protects the eye from exposure keratopathy, chemical injury and trauma

Tape applied across the upper eyelid only

C

Protects the eye from exposure keratopathy

Bio-occlusive dressings

C

Protects the eye from exposure keratopathy, chemical injury and trauma

Ophthalmic ointment

C

Equally effective at preventing corneal abrasions as taping the eyelids closed Allows continuous perioperative monitoring of the eye during nasolacrimal and functional endoscopic sinus surgery Long ocular retention time

C

C

Methylcellulose and hydrogels

C

C

Hydrogel dressing

C

Equally effective at preventing corneal abrasions as taping the eyelids closed and ointments Increase in tear-film stability Allows continuous perioperative monitoring of the eye during nasolacrimal and functional endoscopic sinus surgery

Disadvantages Ineffective in 59% of patients because of lagophthalmus C Unsuitable for operations on the head and neck, and on patients in the lateral or prone position C Inadequate taping results in exposure keratopathy C Possibility of placing the tape directly onto the cornea C Trauma to eyelashes and eyelids on tape removal C Does not adequately protect the eye from chemical injury or trauma C Unsuitable for operations on the head and neck, and on patients in the lateral or prone position C Inadequate application results in exposure keratopathy C Possibility of placing the bio-occlusive dressing directly onto the cornea C Trauma to eyelashes and eyelids on removal of the dressing C Reports of chemical injuries to eyes following the use of ointments containing the preservatives, methylparaben and chlorambutanol C Causes blurred vision in 55e75% of patients C Causes a foreign body sensation in 25e62% of patients C Relatively short ocular retention times C Causes a foreign body sensation in 2e3% of patients C

C

C

Eye pads, with or without shields

C

Reduces the risk of mechanical injury

C

Hydrophilic contact lenses

C

Equally effective at preventing corneal abrasions as taping the eyelids closed and ointments Increase in tear-film stability Protects the eye from exposure keratopathy, chemical injury and trauma, particularly during head and neck procedures

C

C

Suture tarsorrhaphy

C

C C

Not as effective as ointment in preventing corneal abrasions Dressing becomes adherent to underlying tissues if permitted to dry out Must be used with either taping the eyes closed or instillation of ointment/gel to adequately protect the eye Risk of trauma on insertion and removal of the lens

Causes trauma to the eyelids Limits compensatory proptosis of the eyeball in the event of periorbital oedema

Table 1

In contrast, the causes of ischaemic optic neuropathy seem to be multifactorial. There is no safe lower limit for either arterial blood pressure or haematocrit to avoid postoperative vision loss. Hypotension associated with increases in venous pressure, raised

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intraocular pressure and intraorbital pressure, and poor positioning when prone, can jeopardize the eye, especially in patients with vascular risk factors (smoking, hypertension, diabetes, atherosclerosis, polycythaemia).

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When patients are anaesthetized in the prone position, it is imperative that anaesthetists regularly check for globe compression. There is currently no validated recommendation on the frequency of eye checks during anaesthesia. The eyes should be checked whenever a patient’s position is altered (table tilt for instance). We do not know how much pressure needs to be applied (or for how long) to cause retinal ischaemia. The most certain method of preventing globe compression during anaesthesia in the prone position is by suspending the head by skull pins (MayfieldÔ). If pins are not used then face contoured foam headrest with cut-outs for the eyes should be used.12 The main risk factors for ischaemic optic neuropathy are listed below:
prone position
male sex
large blood loss (median 2 litres)
hypotension
prolonged surgery >6 hours. The main risk factors for central retinal artery occlusion are external pressure on the eye and a source of emboli. Ischaemic optic neuropathy and central retinal artery occlusion should be suspected in patients who complain of visual loss on emergence from anaesthesia. An urgent referral to an ophthalmologist for advice on diagnosis and treatment should be sought. Patients with central retinal artery occlusion should have an echocardiogram and carotid ultrasounds to exclude an embolic source. Treatment options for retinal artery occlusion are:
ocular massage, which may dislodge the embolus to a point further down the arterial tree and improve retinal perfusion13
anterior chamber paracentesis (removal of 0.1e0.4 ml of aqueous humour decreases intraocular pressure to 3 mmHg)
intravenous methylprednisolone to reduce optic nerve fibre oedema
increasing perfusion pressure (carbonic anhydrase inhibitor and/or mannitol)
lateral canthotomy and cantholysis
vasodilator therapy or carbogen therapy (5% carbon dioxide, 95% oxygen)
thrombolysis The prognosis for postoperative visual loss remains poor.

production, and tear-film stability. This combination of effects may lead to corneal epithelial drying and loss of lysosomal protection.15 Chemical injury can be caused by cleaning materials on the facemask and inadvertent spillage of antiseptic skin preparations onto the eye. The only antiseptic skin preparation that is not toxic to the cornea is preservative-free povidoneeiodine 10% in aqueous solution.16 It is the agent of choice when antimicrobial skin preparation of the face is required. Antiseptic solutions with detergent readily penetrate the corneal epithelium, causing damage to the underlying iris, ciliary body, lens and blood vessels, leading to ischaemia. Chlorhexidine, cetrimide, aqueous povidoneeiodine containing phenol and alcoholic antiseptic solutions cause oedema and de-epithelialization of the cornea. Trauma to the eyes can occur at anytime during the perioperative period. During induction of anaesthesia it can be caused by ill-fitting facemasks, the laryngoscope, the anaesthetist’s fingers, watchstrap, identification badge or stethoscope. After induction of anaesthesia, trauma to the eyes has been caused by surgical drapes, surgical instruments and patient repositioning. In the postoperative anaesthetic care unit, the patient’s fingers, pulse oximeter probe, pillow, Hudson mask and removal of the occlusive tape from the eyelid may injure the eye. Patients often rub their eyes on emergence from anaesthesia. Placing the pulse oximeter probe on either the little or ring finger of the non-dominant hand can reduce the risk of trauma to the eye. Removal of occlusive tape from the eyelid at the end of surgery should be from the upper eyelid to the lower. Removal of the tape from the lower eyelid to upper causes the upper eyelid to open potentially exposing the cornea to mechanical trauma and exposure keratopathy. There are several methods to protect the eye during surgery and anaesthesia. No single method is completely effective and the various protective strategies may be associated with morbidity (Table 1). Vigilance regarding the perioperative care of the eye is required to reduce these rare but potentially devastating complications. A

REFERENCES 1 The National Health Service Litigation Authority. Reports and accounts. London: The Stationery Office, 2003. 2 Hart WM, ed. Adler’s physiology of the eye. 9th edn. St Louis: Mosby, 1992. 3 Kaiser HJ, Flammer J, Hendrickson P, eds. Ocular blood flow: new insights into the pathogenesis of ocular diseases. Basel: Karger, 1996. 4 Lam AK, Chan ST, Chan B. The effect of age on ocular blood supply determined by pulsatile ocular blood flow and color Doppler ultrasonography. Optom Vis Sci 2003; 80: 305e11. 5 Ozcan MS, Praetel C, Bhatti MT, et al. The effect of body inclination during prone positioning on intraocular pressure in awake volunteers: a comparison of two operating tables. Anesth Analg 2004; 99: 1152e8. 6 Cheng MA, Todorov A, Tempelhoff R, et al. The effect of prone positioning on intraocular pressure in anesthetized patients. Anesthesiology 2001; 95: 1351e5.

Perioperative corneal abrasions The most common ocular complication associated with general anaesthesia is corneal abrasion. Its incidence varies between 0.03% and 0.17%, depending on the method of reporting. Prolonged surgery, lateral or prone positioning during surgery and operations on the head and neck are the main risk factors.14 Corneal abrasions are most commonly caused by exposure keratopathy, chemical injury and direct trauma. General anaesthesia reduces the tonic contraction of the orbicularis oculi muscle, which causes lagophthalmus in up to 59% of patients. If the anaesthetist does not ensure that the eyes are fully closed, exposure keratopathy may occur in 27e44% of patients. Anaesthesia inhibits the protective mechanism afforded by Bell’s phenomena (in which the eyeball turns upwards during sleep, hence protecting the cornea), decreases tear

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7 Hunt K, Bajekal R, Calder I, et al. Changes in intraocular pressure in anesthetized prone patients. J Neurosurg Anesthesiol 2004; 16: 287e90. 8 Grant GP, Szirth BC, Bennett HL, et al. Effects of prone and reverse trendelenburg positioning on ocular parameters. Anesthesiology 2010; 112: 57e65. 9 Shen Y, Drum M, Roth S. The prevalence of perioperative visual loss in the United States: a 10-year study from 1996 to 2005 of spinal, orthopaedic, cardiac and general surgery. Anesth Analg 2009; 109: 1534e45. 10 Williams EL, Hart WM, Templehoff R. Postoperative ischemic optic neuropathy. Anesth Analg 1995; 80: 1018e29. 11 Lee LA, Roth S, Posner KL, et al. The American Society of Anesthesiologists postoperative visual loss registry. Analysis of 93 spine

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12 13 14

15 16

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surgery cases with postoperative visual loss. Anesthesiology 2006; 105: 625e9. Roth S. Perioperative visual loss: what we know, and what can we do? Br J Anaesth 2009; 103(suppl 1): i31e40. Huang E, Gordon K. Retinal artery occlusion. eMedicine, http://www. emedicine.com/emerg/topic777.htm (accessed 14 Feb 2010). Roth S, Thisted RA, Erickson JP, et al. Eye injuries after nonocular surgery: a study of 60,965 anesthetics from 1988 to 1992. Anesthesiology 1996; 85: 1020e7. White E, Crosse MM. The aetiology and prevention of peri-operative corneal abrasions. Anaesthesia 1998; 53: 157e61. Morgan JP, Haug RH, Kosman JW. Antimicrobial skin preparations for the maxillofacial region. J Oral Maxillofac Surg 1996; 54: 89e94.

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OPHTHALMOLOGY

Eye signs in anaesthesia and intensive care medicine

Learning objectives After reading this article you should be able to: C list the eye signs associated with Horner’s syndrome and their significance C describe the eye signs used for brainstem death testing and list the reflex pathways C describe the type of eye responses used in the Glasgow Coma Scale.

Rahul Bajekal

Abstract Eye signs are of limited value in assessing the level of sedation or general anaesthesia. Horner’s syndrome is an important complication of excessively high neuraxial block. Eye opening is part of the Glasgow Coma Scale, and pupil size and reaction have important implications in the intensive care setting.

Saccades Saccades are an abrupt voluntary shift in ocular fixation from one point to another, as occurs when reading. Saccadic eye movements have been used as monitors of sedation. They may be monitored using electro-oculography or infrared oculometry.

Keywords Brainstem death; eyes; intensive care; pupils

Eye signs in general anaesthesia Guedel’s signs Ocular signs were used as part of the clinical assessment of anaesthetic depth. What are commonly known as Guedel’s signs or stages of anaesthesia were a continuum of observations extending from analgesia to overdosage. Eye signs progressed from loss of the eyelash reflex to successive abolition of the eyelid, conjunctival and corneal reflexes. The positions of the eyeball, eye movements and pupil size were also used to assess the depth of inhalational anaesthesia. The opioids, neuromuscular blockade and intravenous techniques have made Guedel’s signs obsolete. Pupillary signs are masked by opioids, and the other signs are of uncertain value.

Eye signs in local and regional anaesthesia Local anaesthesia for eye surgery The success of a retro or peribulbar block may be assessed from the degree to which it achieves an anaesthetized, immobile globe. Horner’s syndrome Ptosis, miosis, nasal congestion and enophthalmos (Horner’s syndrome) indicate high cervical sympathetic blockade. These signs indicate success in a stellate ganglion block, but Horner’s syndrome is seen as a complication in high epidural, subdural, subarachnoid or brachial plexus blockade. Abducens nerve palsy Abducens nerve palsy (VI cranial nerve, lateral rectus muscle of the eye) has been observed as a complication of subarachnoid anaesthesia, sometimes in the absence of a typical post-spinal headache. Most cases resolve without intervention.

Eyelash reflex Anaesthetists commonly test the eyelash reflex during intravenous induction, but the loss of an eyelash reflex does not predict general anaesthesia reliably and should not be used as a measure of depth of anaesthesia.

Dilated pupils Dilated pupils can be caused by brainstem blockade in high subarachnoid or subdural block. Cardiovascular and respiratory effects and loss of consciousness will also occur.

Nystagmus Nystagmus can occur during ketamine anaesthesia.

Verrill’s sign Verrill’s sign (drooping of the eyelid) and loss of the eyelash reflex have been used to assess the adequacy of sedation. These signs are inconsistent, but are usually associated with unacceptably deep levels of sedation. Maintenance of verbal contact with the patient is a better guide to sedation than ocular signs.

Pupillary size Pupillary size has been used to monitor the depth of anaesthesia and opioid overdosage. Though various studies have utilized pupillometry to describe the effect of single drugs, applicability to anaesthesia is limited. Opioids generally cause miosis and a decrease in the velocity of the pupillary light reflex. In equianalgesic doses there is little difference between the various opioids. Mydriasis has been described with pethidine intoxication.

Rahul Bajekal FRCA is Consultant Anaesthetist at Newcastle General Hospital, Newcastle, UK. His interests include anaesthesia for neurosurgery, trauma and upper gastrointestinal surgery. Conflicts of interest: none.

Tears Tears have been used as part of scoring systems for adequacy of level of anaesthesia. Used in conjunction with other signs, they may signify light anaesthesia, but alone they are inadequate markers.

Eye signs in sedation

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Eye signs

Local anaesthesia Sedation General anaesthesia

Intensive care

Sign

Implications

Horner’s syndrome VI nerve palsy, dilated pupils Eye signs unreliable Guedel’s signs (obsolete) Nystagmus Pupil size Glasgow Coma Score Miosis/mydriasis Vestibulo-ocular, corneal, pupillary reflexes Sustained non-reactive pupils

Cervical sympathetic block Spinal anaesthesia Ether anaesthesia Ketamine Opioids Head injury Poisoning Brainstem death Poor recovery after cardiopulmonary resuscitation

Table 1

Eye injury in anaesthesia Blindness due to external pressure on the eye during surgery is devastating. Most cases have been reported after prone surgery when a horseshoe type headrest has been used, but appropriate care must be taken to ensure that the eyes are not compressed whichever position is used. The principal signs associated with external pressure on the eye are blindness, orbital swelling and proptosis, and ophthalmoplegia. Blindness can also result from ischaemic damage to the optic nerve. The visual loss in this condition is characteristically painless, and there are no external ocular signs.

dilated pupils may be seen with massively raised intracranial pressure or imminent coning. Cardiopulmonary resuscitation: the presence of a dilated pupil unreactive to light is sometimes used as an indicator of poor prognosis after cardiopulmonary resuscitation (CPR). During the acute phase of CPR, the administration of anticholinergics may mask underlying pupillary responses. Current guidelines for CPR do not recommend cessation of resuscitative efforts in the presence of dilated non-reactive pupils. The presence of unreactive and dilated pupils in the days following resuscitation suggests a poor prognosis.

Eye signs in intensive care Brainstem death Eye signs remain as diagnostic tests for brainstem death. The neural pathways for ocular reflexes involve the brainstem, and their absence, along with other criteria, is used to confirm absent brainstem activity. Tests include a fixed pupil, unreactive to light regardless of pupillary diameter (afferent II nerve, efferent III nerve) along with the absence of corneal (afferent V nerve, efferent VII nerve) and vestibulo-ocular (afferent VIII nerve, efferent VI, III nerves) to cold caloric testing reflexes (Table 1). The oculocephalic (doll’s eye) reflex is not part of UK brainstem death testing. A

The Glasgow Coma Scale The Glasgow Coma Scale (GCS) uses eye signs as one of its three components. Observations range from no eye response to spontaneous eye opening; the scores for this parameter range from 1 to 4. The GCS does not describe pupil size or responses. Periorbital ecchymoses Periorbital ecchymoses (‘raccoon eyes’) can occur in skull-base fractures. Pupil size and reaction Drugs: the effect of drugs on the pupils may help to diagnose certain cases of poisoning. For example, miosis is seen with organophosphate or opioid overdosage, and mydriasis is seen with drugs such as atropine, tricyclic antidepressants and ecstasy.

FURTHER READING Khan OA, Taylor SRJ, Jones JG. Anaesthesia and saccadic eye movements. Anaesthesia 2000; 55: 877e82. Power C, Crowe C, Higgins P, Moriarty DC. Anaesthetic depth at induction. An evaluation using clinical eye signs and EEG polysomnography. Anaesthesia 1998; 53: 736e43. Wijdicks EFM. Current concepts: the diagnosis of brain death. N Engl J Med 2001; 344: 1215e21.

Third nerve palsy: unilateral or bilateral pupillary dilatation is seen with transtentorial herniation, causing compression of the parasympathetic fibres of the oculomotor (III) nerve. Bilateral

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General anaesthesia for ophthalmic surgery

Learning objectives After reading this article, you should: C have an understanding of which patients may require a general anaesthetic for their eye surgery C be aware of how these patients should be assessed and prepared for anaesthesia C understand the specific problems and issues that relate to each ophthalmic surgical subspecialty.

Nicholas CB Pritchard

Abstract Local anaesthesia for eye surgery is increasingly popular, but there will always be a need for general anaesthesia. Patients may refuse local anaesthesia, may be unable to keep still or lie flat for the duration of surgery or lack the mental facility to cooperate whilst awake. Young children and those with allergy to local anaesthetic also need general anaesthesia. Careful patient preparation is important before surgery. Glycaemic control in patients with diabetes, adjustments to warfarin or aspirin dosing, thromboembolic prophylaxis and preoperative fasting need to be considered. Eye surgery alone is rarely a true emergency, and surgery can usually wait until the patient’s stomach is empty. Eye pathology requiring surgery is a feature of many medical conditions and syndromes. Many patients are elderly with ischaemic heart disease, hypertension, chronic obstructive pulmonary disease and renal impairment, which must be assessed before general anaesthesia. Systemic effects of ophthalmic medications, such as hypokalaemia caused by acetazolamide should be considered. A wide range of general anaesthetic techniques are suitable for eye surgery, but certain key points are relevant to specific operations. These include the oculo-cardiac reflex in strabismus and retinal surgery, the use of intraocular gas bubbles in vitreo-retinal operations, controlled hypotension in lacrimal, orbital and other oculoplastic procedures, and the high incidence of nausea after strabismus surgery. Total intravenous anaesthesia (TIVA) fulfils many of the requirements for the ideal anaesthetic technique for ophthalmic surgery. Blood pressure, heart rate and intraocular pressure are lowered. It is rapidly titratable and recovery is fast. Postoperative nausea is reduced and TIVA works well in patients with renal and hepatic disease. Remifentanil infusion allows nitrous oxide to be avoided and top-up doses of muscle relaxants to be minimized during ventilation. For most ophthalmic surgery, postoperative pain is mild and non-steroidal anti-inflammatory drugs work well. Intraoperative sub-Tenon’s local anaesthetic is useful.

disease is common. Most patients are treated on a day-care basis or require an overnight stay only. Good cooperation between anaesthetist and surgeon is important, and the surgeon requires a ‘soft’, motionless eye on which to operate. Clinical strategies to ensure immobility are vital. An analysis of closed insurance claims by the American Society of Anesthesiologists found that 30% of claims for eye injuries associated with anaesthesia were related to patient movement during surgery.

Preparation of patients Coexistent disease is common in ophthalmic patients and preoperative optimization of medical conditions is required. Investigations can be arranged through the anaesthetic clinic and liaison with appropriate specialists (e.g. cardiologists, neurologists) organized. Eye hospitals are sometimes remote from hospital back-up services such as intensive care and computed tomography scanners. Blood coagulation control: the maximum acceptable international normalized ratio for a patient taking warfarin depends on the operation (e.g. cataract <3.0, eyelid procedures <2.0). Treatment with non-steroidal anti-inflammatory drugs (NSAIDs) or aspirin should not be stopped for cataract surgery but should

Patient selection for general anaesthesia

Keywords General anaesthesia; oculo-cardiac reflex; ophthalmic surgery; remifentanil

Absolute C Patient preference C Young children C Uncooperative patient (e.g. learning difficulties) C Patient unable to keep still (e.g. Parkinson’s disease, dystonia, arthritis, nystagmus, tremor, cough, dyspnoea, vertigo) C Patient unable to lie flat for duration of operation C Allergy to local anaesthesia

The use of local anaesthesia for eye surgery is increasing, but general anaesthesia will always have a place (Box 1). Eye conditions are seldom immediately life threatening and it is nearly always possible to wait for the stomach to empty before giving general anaesthesia. Eye operations are relatively painless procedures; however, patients are often anxious and at the extremes of age. Coexistent

Relative C Surgery to the patient’s only functioning eye C Claustrophobia C Communication problems (e.g. deaf patient, poor language comprehension) C Bleeding disorder C Long procedure

Nicholas CB Pritchard FRCA is Consultant Anaesthetist at Moorfields Eye Hospital, London. He qualified from St Mary’s Hospital, London, and trained in anaesthesia in London. His special interests are oculoplastic, paediatric and intravenous anaesthesia.

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Box 1

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Induction and maintenance of anaesthesia

be stopped at least 10 days before surgery for eyelid procedures. With newer anti-platelet drugs such as clopidogrel, decisions about stopping the drug should be discussed with the prescribing doctor as there may be serious risk (cardiovascular and stent issues) from withholding the treatment.

Airway control A mask should be used for brief procedures only and avoids airway stimulation. The LMA is the ideal airway for most ocular procedures. Insertion and removal of a tracheal tube causes more cardiovascular stimulation than an LMA. Breath-holding, laryngospasm, bronchospasm and coughing are all less likely using an LMA. However, access to the airway during surgery is not easy without serious disturbance to the surgical field; therefore, the LMA must be well positioned and stable before surgery starts. If there is any doubt about the reliability of the LMA position, it is safest to intubate the trachea. Tracheal intubation is required in:  obese patients  long procedures  potential airway soiling e nasal bleeding from lacrimal surgery and harvesting of mucous membrane graft material from inside the mouth (lower lip or palate)  LMA failure  infants having medium-to-long operations  low chest compliance with high airway-inflation pressures. A preformed caudally directed or an armoured flexible tracheal tube, taped away from the eyes, is ideal. Intraocular surgery requires intermittent positive-pressure ventilation, which allows accurate control of expired carbon dioxide, and, therefore, intraocular blood volume and, to a lesser extent, intraocular pressure. Muscle relaxants are not usually required with the LMA if total intravenous anaesthesia is used. Some patients undergoing total intravenous anaesthesia do not maintain their eyes in the neutral position, they either look up or have a divergent squint. This can happen despite adequate depth of anaesthesia with total intravenous anaesthesia, and sometimes a small dose of non-depolarizing muscle relaxant (rocuronium, 10e20 mg, in an adult) is required to correct it and allow surgery to proceed. If muscle relaxants must be avoided the surgeon can use a traction suture to return the eye to a neutral position.

Starvation: the patient should be starved of solids for 6 hours before surgery and of clear fluids for 2 hours. Prophylaxis for deep vein thrombosis: mechanical devices such as compression stockings, calf compressors and ankle elevators are useful. Heparin is usually avoided, especially for retinal and oculoplastic procedures, unless the patient is at high risk. Control of diabetes: patients with diabetes should be given local anaesthesia if possible. If they require general anaesthesia, their operation should be scheduled early on the operating list, and their morning hypoglycaemic tablet omitted. It is usually possible for patients to eat and drink soon after surgery; therefore, patients may be able to omit only their morning insulin dose. Drug treatment should be continued in most patients, especially cardiac drugs, antihypertensives, bronchodilators and corticosteroids. It should be remembered that eyedrops and other ophthalmic drugs have systemic effects (Table 1). Premedication may be required. The patient should be given anti-emetics if they have a history of postoperative nausea and vomiting (PONV) or if they are having an emetogenic operation. Antihistamines (H2-blockers) should be considered if gastric acidity or oesophageal reflux is a problem, particularly if a laryngeal mask airway (LMA) is to be used. Anxiolytics may be given if needed, but should be avoided for day surgery. Antimuscarinics should be given to children having ketamine for glaucoma screening. Topical anaesthetic cream should be used for children and patients with needle phobia. Marking the side: the surgeon must mark the correct side for surgery before the patient leaves the ward. This is rechecked on arrival in the theatre suite and again in the anaesthetic room before induction. The eye that does not require surgery is taped closed after induction of anaesthesia. The surgeon and scrub nurse should check which eye requires surgery for a final time just before cleaning the eye in the theatre.

Intravenous fluids Provided there is only a small amount of blood loss there is no need for intraoperative fluids other than maintenance crystalloid solutions. A full bladder causes hypertension and elevates intraocular pressure. Anaesthetic maintenance drugs Most standard methods of maintaining anaesthesia are possible. Either of the following work well for almost any combination of ocular operation and patient:  LMA e remifentanil (Box 2) plus propofol/oxygen/air  tracheal tube e remifentanil plus sevoflurane/oxygen/air, with or without muscle relaxant for intubation. The relatively unstimulating nature of most ophthalmic surgery can cause problems during general anaesthesia. Patients often become hypotensive, and sympathomimetics (e.g. ephedrine, metaraminol) should be used to maintain blood pressure and heart rate. However, awareness and patient movement are hazards if a proper level of anaesthesia is not maintained. In particular, accidental movement of the tracheal tube by the surgeon can cause coughing. The use of a peripheral nerve stimulator can be more of a stimulus than the operation

Systemic effects of ophthalmic drugs Drug

Effect

b-blockers

Hypotension, bradycardia, bronchoconstriction Hypertension Hypokalaemia Prolonged action of neuromuscular junction blockers broken down by pseudocholinesterases

Phenylephrine Acetazolamide Ecothiopate

Table 1

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Posture: after vitrectomy with injection of intraocular gas, the patient will have to posture as soon as they are conscious. A facedown position or with ‘one cheek to pillow’ is usual. Following oculoplastic surgery, patients are usually nursed in a sitting position.

Benefits of remifentanil for ocular surgery C

C C C C

C C C

Produces stable, low, controllable blood pressure and heart rate, and therefore intraocular pressure Rapidly titratable to patient needs Avoids need for maintenance muscle relaxants Rapid and unique recovery profile with no residual effects Dose and duration of infusion have almost no effect on recovery e ideal for long operations Low incidence of nausea e particularly with propofol Avoids use of nitrous oxide in vitrectomy with gas injection Well tolerated in patients with renal and hepatic disease

Specific considerations for surgical subspecialties Vitreo-retinal Scleral buckle with or without cryotherapy: pain, PONV, and oculocardiac reflex are often marked, especially in young adults. Vitrectomy: the type of gas injected after vitrectomy, to provide retinal tamponade, depends on the required duration of action (Table 2) The patient will have to posture postoperatively so that the gas bubble lies over the appropriate area of the retina. Since the introduction of heavy perfluorocarbon liquids in vitreoretinal surgery, the need for intraoperative posturing (including turning the patient prone) has been eliminated. Patients must not travel by aeroplane or be exposed to nitrous oxide while the gas bubble is present. Nitrous oxide is 34 times more soluble in blood than nitrogen. Administered nitrous oxide rapidly diffuses into the intraocular gas bubble, leading to a large increase in bubble volume and intraocular pressure, which may cause central retinal artery occlusion and blindness. If nitrous oxide is used during the anaesthetic for vitrectomy it must be discontinued at least 15 minutes before gas-bubble injection.

Box 2

(particularly anterior segment procedures) and can induce movement or coughing. Monitoring Spirometry is useful for identifying changes in the position of an LMA during surgery. Increased peak airway pressure, decreased compliance, reduced tidal volumes and a difference between inspired and expired tidal volume should be looked for. Invasive arterial pressure monitoring is useful if profound induced hypotension is required. Central venous pressure monitoring is seldom required. There is an association between malignant hyperpyrexia and oculomuscular abnormalities. However, the usual problem is hypothermia, which may cause shivering postoperatively. Postoperative shivering is most common after long procedures in young fit males having total intravenous anaesthesia. Intravenous pethidine can stop this shivering. It is important to monitor the skin or nasopharyngeal temperature. Warming mattresses, warm air-blowing devices and circle breathing systems may be used to maintain body temperature. There is seldom any need to expose the body below the neck. Therefore, patients can often be kept warm with blankets. Depth of anaesthesia monitoring (e.g. bispectral index) is useful in ophthalmic surgery, particularly during long, relatively non-stimulating procedures in elderly patients, in whom low doses of anaesthetic may be adequate to prevent awareness and patient movement.

Oculoplastics Oculoplastic operations are often undergone by elderly patients, or children with conditions such as Goldenhar’s syndrome. Antiplatelet drugs must be stopped for 10 days before these procedures, particularly eyelid surgery, are done. Orbital Blood loss is possible during major orbital surgery, such as threewall orbital decompression procedures for thyrotoxic exophthalmos, and tumour resections. Transfusion of blood is seldom required, but induced hypotension with head-up positioning and maintenance of low-to-normal arterial carbon dioxide tensions help to improve the surgical field and reduce bleeding. Retrobulbar or sub-Tenon’s local anaesthetic infiltration is useful during enucleation surgery to reduce postoperative pain.

Postoperative management Pain: NSAIDs and paracetamol/codeine mixtures are usually adequate to control pain. The surgeon can perform a sub-Tenon’s local anaesthetic infiltration towards the end of surgery to provide good postoperative analgesia. Severe pain and nausea may result from raised intraocular pressure. This may be caused by a specific surgical complication, and the patient should be examined by the operating surgeon rather than be treated for the symptoms. Intraocular pressure can be reduced in the short term by acetazolamide, 500 mg intravenously over 5 minutes, or mannitol, 1 g/kg intravenously over 30 minutes.

Glaucoma In patients with glaucoma, reduction of the intraocular pressure is desirable. All anaesthetic agents except ketamine and

Gases used for retinal tamponade

Extubation can be performed during deep anaesthesia with spontaneous breathing. It is important that the patient avoids coughing and straining on the tracheal tube. Awake extubation, especially after a remifentanil-based technique, is very safe and is the author’s favoured method of extubating the patient’s trachea.

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Gases used (non-expansile)

Time in eye until bubble clears

Air Sulphur hexafluoride (SF6) 20% (with air) Octafluoropropane (C3F8) 14% (with air)

2e3 days 2e3 weeks 55 days ( 15)

Table 2

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suxamethonium reduce intraocular pressure. Local anaesthetic injection can further compromise optic nerve function and retinal perfusion by increasing intraocular pressure in patients with advanced glaucoma. Intubation (and extubation) of the trachea, can cause rises in intraocular pressure of up to 50 mmHg. LMA insertion is much less stimulating and should be used if possible.

above are done, particularly if the patient is having total intravenous anaesthesia or other drugs that increase vagal tone. This pretreatment will reduce the chance of bradycardia not abolish it. Further doses may be required. Local anaesthetic infiltration around the muscles abolishes the afferent pathway. Non-depolarizing muscle relaxants also reduce the incidence of the reflex by reducing extraocular muscle tone. There is a decrease in incidence with increasing age.

Cataract Cataract operations are short and the surgical stimulus is low, therefore they are usually carried out under local anaesthesia. The use of LMA and total intravenous anaesthesia is good for anterior segment surgery.

The ‘open eye’ In an open eye, the intraocular pressure is the same as atmospheric pressure. The danger is of expulsion of ocular contents. It is seldom necessary to operate on an isolated eye injury as an emergency. However, a patient may have other injuries that do require urgent surgery. Penetration of the eye by copper fragments may be another exception, but even then a delay for stomach emptying is usually possible. Do not try to empty the stomach with a nasogastric tube. An LMA can be used for open eye surgery, subject to the restrictions mentioned above. For open eye surgery the following should be noted:  avoid ketamine and suxamethonium, which increase intraocular pressure  aim for a smooth, rapid induction. Rocuronium, 1 mg/kg, is suitable for muscle relaxation  some degree of head-up tilt may be maintained during induction  avoid mask pressure directly on the eye  do not rush intubation. Wait for the induction drugs to have full effect  coughing, straining or gagging during premature intubation attempts can lead to loss of ocular contents. A

Commonly discussed topics The oculo-cardiac reflex Operations associated with the oculo-cardiac reflex include:  squint  scleral buckle retinal repair  orbital implant  evisceration  enucleation. The oculo-cardiac reflex is mediated via the trigeminal afferent with vagal efferent. It manifests as a slowing in the sinus rate, which may become irregular. Sinus arrest with asystole can occur but recovers when the precipitating cause (usually a surgeon pulling on the muscle) is abolished. Other arrhythmias that may be seen include atrioventricular junctional rhythms, wandering pacemakers, extrasystole and bigeminy. Prophylactic antimuscarinic drugs (glycopyrrolate 200e400 mg (child, 4e8 mg/kg) or atropine 300e600 mg (child, 20 mg/kg)) should be given after induction, before the operations listed

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Anaesthesia for eye surgery in paediatrics

Learning objectives After reading this article, you should: C have an understanding of general anaesthetic considerations for children and infants undergoing eye surgery C recognise effects on the eye from congenital syndromes and oculo-cardiac reflex C understand control and measurement of intra-ocular pressure and anti-emetic regimes.

Jonathan Lord

Abstract Children and infants present for ophthalmic surgery from birth onwards. This article looks at the general anaesthetic considerations for these patients with respect to eye surgery, with particular reference to control of intra-ocular pressure, oculo-cardiac reflex, ocular trauma, postoperative nausea and vomiting, malignant hyperpyrexia, syndromes and analgesia. Specific problems such as the measurement of intra-ocular pressure, and techniques for both intra- and extra-ocular surgery are then discussed.

Venous pressure e the venous drainage from the eye is valveless and so any changes in venous pressure produce an immediate change in ocular pressure by altering the volume of blood within the choroid. Raised venous pressure also impedes aqueous drainage via the canal of Schlemm and hence a secondary rise in IOP. Coughing, straining and retching all increase venous pressure. A 15 head-up tilt will reduce it.

Keywords Airway; hyperpyrexia; intra-ocular pressure; ketamine; postoperative nausea and vomiting

Arterial pressure e mean arterial pressure (MAP) has little effect on IOP, but sudden increases in MAP will produce a rapid and unpredictable rise in IOP. Children present for ophthalmic surgery from the neonatal period onwards. Neonates and infants usually present for cataract extraction and treatment for congenital glaucoma whereas older children more often have strabismus, lacrimal, vitreo-retinal or ocular plastic surgery. These children may often present for repeated procedures and skilled anaesthesia will contribute to a successful operative result. The problems of anaesthesia are essentially the same as those of paediatric anaesthesia in any field, however there are some areas that require particular attention.

Arterial PCO2 e alterations in PCO2 have a linear effect on IOP. A reduction causing a fall in choroidal volume and hence in IOP and vice versa. Aqueous volume: although alteration of this is the mainstay of glaucoma therapy it is of limited importance during anaesthesia as without direct drainage the volume alters slowly. Acetazolamide reduces aqueous production and hence reduces IOP. Vitreous volume: again this is of limited importance during anaesthesia. Osmotic diuretics such as mannitol can dehydrate the vitreous and hence reduce its volume.

General considerations Airway Although not strictly a ‘shared airway’ most ophthalmic operations involve draping the head and hence abolish or at least reduce access to the airway.

External pressure: direct pressure on the eye with masks, etc. must be avoided. Increase in tone of the extra-ocular muscles will increase IOP which means that depolarizing muscle relaxants, such as suxamethonium, causes an increase in IOP. The rise produced by suxamethonium being maximal at 2 minutes and lasting for 5 minutes. Pre-treatment with non-depolarizing muscle relaxants to prevent this has been advocated but is of unproven value.

Intra-ocular pressure (IOP) Normal IOP is between 10 and 22 mmHg. The factors that affect IOP are essentially the same as those that affect intra-cranial pressure. The control of IOP is an important part of the anaesthetic management for intra-ocular surgery. Any sudden increase in IOP with an open eye will lead to loss of ocular contents and/ or an expulsive haemorrhage. The likely outcome of such an event being loss of vision. The main factors involved in the regulation of IOP are the choroidal, aqueous and vitreous volumes together with external pressure.

Oculo-cardiac reflex pathway Long and short ciliary nerves

Heart

Ciliary ganglion

Vagus

Choroidal volume: this can be affected by venous pressure, arterial pressure and arterial PCO2.

(via ophthalmic division V nerve) Gasserian ganglion

Jonathan Lord FRCA is Consultant Anaesthetist at Moorfields Eye Hospital, London, UK. His specialist interest is paediatric ophthalmic anaesthesia. Conflicts of interest: none declared.

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Trigeminal sensory nucleus (in floor of IV ventricle)

Figure 1

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Anti-emetic drugs for postoperative nausea and vomiting

Congenital syndromes

Drug Ondansetron

Dose Comments 0.1e0.15 mg/kg Excellent anti-emetic (max 8 mg) Low side-effect profile Cyclizine 1 mg/kg (max 50 mg) Effective, but sedative Dexamethasone 200e300 mg/kg Very effective, particularly (max 8 mg) squint and orbital implants Table 1

Syndrome

Ocular manifestation

Down’s

Strabismus Cataract

Goldenhar Homocystinuria

Ptosis Lens dislocation

Marfan

Lens dislocation Retinal detachment Retinopathy

Anaesthetic significance Cardiac problems Hypothyroidism Blood dyscrasias Difficult intubation Thromboembolism Hyperinsulinaemia Heart valve defects Thoracic aneurysms Sickle crisis

Retinal detachment Secondary glaucoma

None Epilepsy

Sickle haemaglobinopathies Stickler SturgeeWeber

Oculo-cardiac reflex This is a potent reflex in children. The afferent and efferent pathways are shown in Figure 1. It can be triggered by increases in IOP, traction on the extraocular muscles, trauma or pain. It usually produces a bradycardia, but asystole will quickly ensue in children if left untreated. Other arrhythmias such as nodal rhythms and

Table 2

Pain management protocol Postoperative analgesia should be considered as part of the overall plan of anaesthesia A multimodal approach using the following groups is logical: Local anaesthesia Paracetamol NSAIDs Opioids Local anaesthesia should be used whenever possible plus other analgesics as follows: Severe pain (i.e Evisceration) Bad pain (i.e Strabismus surgery) Moderate pain (i.e Intra-ocular surgery) Mild pain (i.e EUA) Paracetamol

Paracetamol, NSAID + morphine

Paracetamol, NSAID + codeine

Paracetamol + NSAID >6/12

EUA, examination under anaesthesia; NSAID, non-steroidal anti-inflammatory drug.

Table 3

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ventricular fibrillation can also occur. Without any preventative treatment the reported incidence varies from 30 to 90%. Pretreatment with a vagolytic is protective. Oral atropine can be given as part of the premedication, intravenous atropine or glycopyrrolate can be given peroperatively. Infiltration around the extra-ocular muscles with local anaesthesia also reduces the reflex. It is important that a pulse monitor with an audible bleep is used peroperatively so that both the anaesthetist and the surgeon can hear if a bradycardia occurs.

Anaesthetic technique for IOP measurement Premedication Oral atropine 30 mg/kg body weight 1 hour pre-op Oral midazolam 0.5 mg/kg body weight 1 hour pre-op Ametop over convenient vein Induction

IV ketamine (50 mg/ml strength) 1e2 mg/kg body Onset 30 seconds Duration 5e10 minutes OR IM ketamine (100 mg/ml strength) 10 mg/kg Onset 2e8 minutes Duration 10e20 minutes IV access after induction OR Inhalational induction O2 and sevoflurane up to 8% IV access IV ketamine as above After inhalational induction it is advisable to wait 5 minutes before measuring IOP to allow for sevoflurane washout

Acute ocular trauma The question of how to deal with acute ocular trauma and the unstarved child is frequently discussed. Many centres get round the problem by avoiding emergency surgery as there is no evidence that waiting for the child to be starved influences the outcome of surgery. Unfortunately 6 hours’ starvation in a traumatized child does not mean that the stomach will be empty and consideration needs to be given to this. Prokinetics such as metoclopramide together with H2 blockers such as ranitidine to increase stomach pH can be given. The management of the anaesthetic is controversial but the need to avoid suxamethonium if the eye is open as loss of contents from the rise in IOP can occur is paramount. The author’s opinion is that induction of anaesthesia should be either intravenous with a fast-acting non-depolarizing muscle relaxant such as

IM, intramuscular; IOP, intra-ocular pressure; IV, intravenous; pre-op, preoperatively.

Table 4

Anaesthesia for intra-ocular surgery Premedication Midazolam 0.5 mg/kg orally if required Ametop to a suitable vein Induction IV access Remifentanil 1 µg/kg Propofol 2–3 mg/kg

Inhalational – O 2 + sevoflurane IV access Rocuronium 0.6 – 0.9 mg/kg Laryngeal mask airway Or Endotracheal tube Maintenance

IPPV with O 2 + air Remifentanil IVI 0.2 – 0.5 µg/kg/minute Propofol IVI 4–8 mg/kg/hour

IPPV with N2O + O 2 + sevoflurane

Analgesia Diclofenac 1–2 mg/kg per rectum And/or Paracetamol 20–30 mg/kg per rectum or 20 mg/kg IV Anti-emetic Ondansetron 0.15 mg/kg IV And Dexamethasone 200–300 µg/kg (max 8 mg) Reversal Neostigmine 50 µg/kg + glycopyrrolate 10 µg/kg

Nil required IVI, intravenous infusion; IPPV, intermittent positive pressure ventilation

Figure 2

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Anaesthesia for strabismus surgery Premedication Midazolam 0.5 mg/kg orally if required Atropine 30 µg/kg orally Ametop to a suitable vein Induction IV access Remifentanil 1 µg/kg Propofol 2–3 mg/kg + if atropine premedication omitted glycopyrrolate 5 µg/kg

Inhalational – O 2 + sevoflurane IV access + if atropine premedication omitted glycopyrrolate 5 µg/kg

Laryngeal mask airway

Maintenance IPPV with O 2 + air + sevoflurane Remifentanil IVI 0.2 – 0.5 µg/kg/minute

SV with N2O + O 2 + sevoflurane

Analgesia Diclofenac 1–2 mg/kg per rectum And/or Paracetamol 20–30 mg/kg per rectum or 20 mg/kg IV And/or Codeine phosphate 1 mg/kg IM or per rectum Anti-emetic Ondansetron 0.15 mg/kg IV And Dexamethasone 200 to 300 µg/kg (max 8 mg) IM, intramuscularly; IVI, intravenous infusion; IPPV, intermittent positive pressure ventilation; SV, spontaneous ventilation

Figure 3

rocuronium or inhalational. Intubation is preferable to protect the airway. The child should then be extubated awake.

considered mandatory. All anaesthetic departments should ensure that personnel are aware of the recommendations for treatment of MH as well as the location of the necessary drugs within the department.

Postoperative nausea and vomiting (PONV) Ocular procedures in general are emetic and if consideration is not given to this a high proportion of children will have PONV. It is produced as a result of the manipulation of the extra-ocular muscles, by alterations in the intra-ocular pressure or by volume expansion within the orbit. It is important to stress that any child with persistent vomiting following an intra-ocular procedure must be checked by the surgeon to exclude raised IOP as the cause. As always prevention is better than cure and suggested drugs are shown in Table 1.

Analgesia Most ophthalmic operations are not particularly painful and simple analgesia in the form of paracetamol and other nonsteroidal anti-inflammatories are all that are required. The main exceptions to this are strabismus surgery where the muscle necrosis following suturing can cause marked pain, detachment surgery where an encircling band is used and larger procedures such as tumour resection or eviscerations. In all operations considerations should be given to all modalities of analgesia and a suggested regime is given in Table 3. Local anaesthesia can take the form of topical local anaesthetic drops or formal local blocks. Sub-Tenon anaesthesia being particularly useful in strabismus and detachment surgery.

Associated syndromes Eye abnormalities in children are frequently manifestations of multisystem disorders. Many of these syndromes have anaesthetic significance and it is important that any anaesthetist involved in paediatric ophthalmology is on the lookout for any associated problems. A sample of the commoner syndromes is shown in Table 2.

Specific problems Measurement of intra-ocular pressure (IOP) Glaucoma can be defined as a progressive optic neuropathy and if left unchecked will eventually result in blindness. The effective management of children with glaucoma includes the accurate

Malignant hyperthermia (MH) This is stated to be more common in ophthalmic and in particular strabismus surgery. Temperature measurement should therefore be

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measurement of their IOP. In the pre-school group (under 5 years) this usually requires an anaesthetic. All currently available anaesthetic agents have an effect on IOP. With the exception of ketamine they all reduce IOP. This extent of this reduction is both unknown and not reproducible even in the same individual. This can lead to misleading readings of IOP and have a detrimental effect on treatment.

Ketamine resistance: children having multiple frequent ketamine anaesthetics can develop an unpredictable resistance to ketamine necessitating escalating doses. This resistance resolves if ketamine is avoided for a few weeks. Intra-ocular surgery The key to successful intra-ocular surgery is a balanced general anaesthetic with intermittent positive pressure ventilation. Two suitable schemes are shown in Figure 2. The anaesthetic should be planned to try and avoid any of the factors previously described that may increase IOP.

Ketamine: this is the drug of choice for IOP surveillance. It is a phencyclidine derivative that produces dissociative anaesthesia via its action at the NMDA receptors. It produces either no change or a transitory rise in IOP due to a combination of its sympathomimetic effects and extra-ocular muscle contraction. Studies suggest however that this rise is not seen if the child is premedicated with a benzodiazepine. A suggested technique for ketamine anaesthesia is shown in Table 4. It is unnecessary to secure the airway and the child should be allowed to breathe spontaneously in room air. Supplemental oxygen is occasionally required. Premedication with a benzodiazepine is essential causing amnesia, which is useful in repeated anaesthetics in children, ‘ketamine sparing’ so allowing the dose of ketamine to be reduced and also reducing emergence phenomena. Ketamine causes excessive salivation and should always be used in conjunction with an anticholinergic to reduce the risk of laryngeal spasm. Finally ketamine is emetic and routine anti-emetic administration is required.

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Extra-ocular surgery The bulk of this consists of strabismus and lacrimal duct surgery. These can be performed with either a straight forward spontaneously breathing anaesthetic or a balanced general anaesthetic with intermittent positive pressure ventilation. In strabismus surgery consideration must be given to analgesia, avoidance of the oculo-cardiac reflex and anti-emesis. A suggested approach is shown in Figure 3. A

FURTHER READING Mather SJ. A handbook of paediatric anaesthesia. Oxford University Press, 1996. Miller RD. Miller’s anesthesia. 7th edn. Philadelphia: Churchill Livingstone, 2010.

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Local anaesthesia for ocular surgery

Learning objectives After reading this article, you should: C have an understanding of which patients are suitable for ocular surgery under local anaesthesia and which require general anaesthesia. C understand the anatomy of the eye including motor and sensory innervation. C understand the advantages and disadvantages of the different techniques including topical, local, retrobulbar, peribulbar and sub-Tenon’s block.

Caroline Carr

Abstract Cataract surgery is routinely performed under local anaesthesia. With modern surgical techniques, adequate operating conditions can often be provided by topical anaesthesia alone. For more complex procedures and for prolonged operations such as vitreo-retinal surgery a local block is required. Historically, the sharp needle techniques of retrobulbar and peribulbar eye block have been used. However, the occurrence of rare but sight-threatening complications such as retrobulbar haemorrhage and globe perforation have led to the adoption of the technique of sub-Tenon’s block, which avoids the use of sharp needles. A thorough knowledge of ocular anatomy is essential before proceeding with any eye block technique. Patients who receive local anaesthesia for ocular surgery require careful preoperative assessment and stabilization of concomitant medical conditions. The intended procedure should be explained to the patient to ensure their cooperation and reduce anxiety.

General considerations Absolute contraindications Absolute contraindications to ocular local anaesthesia are the same as for any local anaesthetic technique: patient refusal, inability to cooperate and lie still, presence of local sepsis, and allergy to the local anaesthetic agents. Relative contraindications These are previous or repeated surgery, when local anaesthesia techniques may become technically difficult, and in the open eye such as a ruptured globe when the contents are at risk of expulsion.

Keywords Cataract surgery; sub-Tenon’s anaesthesia; topical anaesthesia; vitreo-retinal surgery

Preoperative assessment The patient’s concomitant medical conditions should be controlled before surgery. Medical history, examination and special tests are targeted to this end. Of particular relevance to ocular surgery under local anaesthesia are the presence of chronic cough, breathlessness and disorders of movement such as Parkinson’s disease. These must be carefully assessed with respect to the patient’s ability to lie flat and still for the surgery. For patients receiving anticoagulation therapy, their international normalized ratio should be maintained within therapeutic limits (2e3) for ocular surgery under topical, peribulbar or subTenon’s anaesthesia.1 Patients do not need to starve preoperatively.

Surgery of the eye and its surrounding structures can readily be performed under local anaesthesia. General anaesthesia is reserved for those unable to cooperate, such as children, or those receiving bilateral surgery or complex or lengthy procedures. Routine cataract surgery is usually performed under local anaesthesia and efforts have concentrated on finding methods that have few serious complications. Occasionally serious systemic complications of ophthalmic local anaesthesia may occur, especially in medically compromised patients. In recognition of this the Joint Working Party report on Anaesthesia in Ophthalmic Surgery1 recommends that an anaesthetist is included in the team managing patients for ocular surgery under local anaesthesia.

Motor innervation of the eye Anatomy Muscle Inferior oblique Superior rectus Inferior rectus Medial rectus Levator palpebrae superioris Superior oblique Lateral rectus Orbicularis oculi

With any local anaesthetic technique a detailed knowledge of anatomy is essential (pages 438e443). Motor innervation is from cranial nerves III, IV, VI and VII (Table 1), and sensory innervation is via the ophthalmic and maxillary divisions of cranial nerve V (trigeminal) (Table 2).

Caroline Carr MA FRCA is a Consultant Anaesthetist and Service Director at Moorfields Eye Hospital, London, UK. Apart from ophthalmic anaesthesia her special interest is clinical governance. Conflicts of interest: none declared.

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Nerve supply Oculomotor (III) Oculomotor (III) Oculomotor (III) Oculomotor (III) Oculomotor (III) Trochlear (IV) Abducens (VI) Facial (VII) temporal and zygomatic branches

Table 1

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Sharp needle blocks Retrobulbar block: provided good akinesia and anaesthesia, and was usually supplemented with a facial nerve block to paralyse orbicularis oculi. The principle of the technique was to deposit a small volume (2e3 ml) of anaesthetic solution in the muscle cone at the apex of the orbit using a 40 mm-long needle. Rare, but serious, complications occurred with these blocks, including retrobulbar haemorrhage, globe perforation, damage to the optic nerve or ophthalmic artery, and spread of the anaesthetic to the brainstem along the optic nerve dural sheath.6

Sensory innervation of the eye Structures Sclera, cornea, iris and ciliary body Conjunctiva e superior

Conjunctiva e inferior Conjunctiva e lateral Conjunctiva e limbal Periorbital skin

Nerve supply Short ciliary nerves Long ciliary nerves Supraorbital nerve Supratrochlear nerve Infratrochlear nerve Infraorbital nerve Lacrimal nerve Long ciliary nerves Supraorbital nerve Supratrochlear nerve Infraorbital nerve Lacrimal nerve

Peribulbar block: was introduced in 1986 to avoid the complications of retrobulbar block. A shorter needle places larger volumes of anaesthetic solution outside the muscle cone with the needle tip no further back than the equator. The anaesthetic spreads throughout the orbit and provides satisfactory operating conditions. The technique usually consists of two injections of local anaesthetic, one inferior and one medial to the globe. These sites are selected to avoid vital structures within the orbit. The volume used is usually enough to block the nerves to orbicularis oculi directly and avoid facial nerve block. Adaptations of the technique have been to direct the lateral injection up into the muscle cone just behind the globe. This produces a more rapid reliable onset of block with a smaller volume of anaesthetic solution, and frequently the medial injection is dropped. This is the ‘modern retrobulbar’ technique. Any technique using a blindly placed sharp needle may result in serious sight-threatening complications, including globe perforation. Sub-Tenon’s block is now commonly used for most surgery on the globe.

Table 2

Choice of anaesthetic The surgeon’s preference, the intended surgery, the ocular anatomy and the patient’s preference all need to be taken into consideration when choosing the anaesthetic technique.2 These should be considered at the preoperative assessment visit and the technique to be used explained carefully to the patient and supplemented with leaflets and other patients’ experiences.3 A very anxious patient may be suitable for combined sedation and local anaesthesia. Alternatively, general anaesthesia may be the best option.

Sub-Tenon’s block: local anaesthesia is introduced to the subTenon’s space through a single small incision in the inferonasal quadrant of the eye.7 Posterior diffusion of the anaesthetic blocks sensation from the eye by direct action on the ciliary nerves as they pass through the sub-Tenon’s space. If a suitable volume of anaesthetic is used, complete akinesia is obtained as it diffuses into the muscle cone from the sub-Tenon’s space.8 This technique is commonly used for cataract surgery, with lower reported serious complications than for sharp needle techniques,9 but is also increasing in popularity for vitreoretinal surgery.10

Techniques of local anaesthesia Topical anaesthesia Topical anaesthesia provides good surface anaesthesia of the globe without the complications of a regional block. The patient retains full eye movement. Commonly used for superficial surgery of the conjunctiva and cornea, including removal of sutures and small foreign bodies, topical anaesthesia alone is now frequently used for cataract surgery.4 With the newer techniques of surgery, akinesia and reduction of intraocular pressure are not of such importance. Patients experience discomfort owing to sensation from the iris and ciliary body,5 but this can be abolished by intracameral preservative-free lidocaine 1%, up to 1 ml. Local infiltration Local infiltration of the skin with anaesthetic is used for eyelid surgery in adults. For anaesthesia of deeper structures, the supraorbital and infraorbital branches of the trigeminal nerve are blocked where they emerge from the supraorbital notch and infraorbital foramen. 0.5% bupivacaine, 1e2 ml, with epinephrine 1:200,000 is injected subcutaneously at each site. To avoid subcutaneous haemorrhage:  aspirin should be stopped 2 weeks preoperatively  warfarin should be stopped 3 days preoperatively  injection into deeper tissues should be avoided  epinephrine 1:200,000 should be used as a vasoconstrictor in the local anaesthetic solution.

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Figure 1 Sub-Tenon’s block e pinch conjunctiva and Tenon’s with forceps.

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Figure 4 Sub-Tenon’s block e pass cannula into sub-Tenon’s space.

Figure 2 Sub-Tenon’s block e snip through both layers.

 Sub-conjunctival haemorrhage is kept to a minimum by using topical epinephrine 1:10,000, avoiding cutting conjunctival vessels and extensive dissection, and using gentle, direct pressure. Different cannulae can be used with similar effectiveness.11 Although safer for routine cataract surgery, 12 sight-threatening complications can still occur with sub-Tenon’s block,13 and the anaesthetist must always be aware of the risks.

Technique of sub-Tenon’s block (Figures 1e4)  The patient lies supine with their head on a pillow.  A few drops of topical anaesthetic are placed on the conjunctiva.  A few drops of 5% aqueous iodine are placed on the conjunctiva.  A small speculum is inserted to hold the eyelids apart.  The patient looks up and laterally.  The conjunctiva and Tenon’s capsule are pinched firmly with non-toothed forceps, 5e7 mm from the limbus in the inferonasal quadrant.  With round-ended spring scissors a small snip is made through both layers.  The closed scissor tips are passed through the hole, and the blades are opened while gently withdrawing them to form a short tunnel.  A blunt, curved 19G, 25 mm sub-Tenon’s cannula is passed into the sub-Tenon’s space and allowed to slide round the globe, over the sclera to a depth of 15e20 mm in the inferonasal quadrant.  The appropriate volume of local anaesthetic is slowly injected to minimize chemosis: 4 ml for cataract surgery, 5e6 ml for a trabeculectomy or corneal graft, and 8e10 ml for vitreoretinal procedures.  The cannula is withdrawn and slight pressure maintained over the closed eye for a few minutes when complete akinesia and anaesthesia are seen.

The local anaesthetic mixture The characteristics of a block will depend on the anaesthetic solution used as well as the technique. 2% lidocaine is effective within 5 minutes, and will give 30e40 minutes of surgical anaesthesia. 0.5% bupivacaine has a slower onset of action but longer duration of surgical anaesthesia (up to 4 hours) and is useful when postoperative analgesia is required. Ropivocaine has been used successfully in peribulbar blocks but has little advantage over bupivacaine in the small volumes needed in eye blocks. Mixtures of lidocaine and bupivacaine are frequently used to provide rapid onset with delayed offset, but are of no practical advantage. Addition of 1:200,000 epinephrine reduces haemorrhage in skin infiltration techniques but is not used in orbital blocks because the vasoconstriction may compromise retinal blood flow. The enzyme hyaluronidase in concentrations of 5e30 IU/ml enhances the spread of anaesthetic and speed of onset.

Patient management During surgery the patient should be monitored with a pulse oximeter and electrocardiography, and non-invasive blood pressure monitoring should be available if required. Trained staff should monitor the patient and the anaesthetist should be available for resuscitation or sedation. Sedation Most patients readily tolerate ocular surgery under local anaesthesia with careful explanation, gentle handling and a sympathetic approach. Occasionally the very anxious patient may require sedation for cataract surgery. In vitreo-retinal surgery the patient may require sedation to enable them to tolerate the longer operating time. Various techniques may be used with appropriate monitoring; remembering that draping the head for surgery will reduce access to the airway. A small dose of intravenous

Figure 3 Sub-Tenon’s block e form a tunnel with scissors.

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6 Rubin AP. Complications of local anaesthesia for ophthalmic surgery. Br J Anaesth 1995; 75: 93e6. 7 Stevens JD. A new local anaesthesia technique for cataract surgery by one quadrant sub-Tenon’s infiltration. Br J Ophthalmol 1992; 76: 670e4. 8 Winder S, Walker SB, Atta HR. Ultrasonic localization of anesthetic fluid in sub-Tenon’s, peribulbar, and retrobulbar techniques. J Cataract Refract Surg 1999; 25: 56e9. 9 Eke T, Thompson JR. Serious complications of local anaesthesia for cataract surgery: a 1 year national survey in the United Kingdom. Br J Ophthalmol 2007; 91: 470e5. 10 Lai MM, Lai JC, Lee WH, et al. Comparison of retrobulbar and subTenon’s capsule injection of local anaesthetic in vitreoretinal surgery. Ophthalmology 2005; 112: 574e9. 11 McNeela BJ, Kumar CM. Sub-Tenon’s block with an ultrashort cannula. J Cataract Refract Surg 2004; 30: 858e62. 12 Kumar CM, Williamson S, Manickam B. A review of sub-Tenon’s block: current practice and recent development. Eur J Anaesthesiol 2005; 22: 567e77. 13 Ruschen H, Bremner FD, Carr C. Complications after sub-Tenon’s eye block. Anesth Analg 2003; 96: 273e7.

midazolam, 0.5e1.5 mg, before the anaesthetic, provides amnesia while avoiding over-sedation. A

REFERENCES 1 Local anaesthesia for intraocular surgery. The Royal College of Anaesthetists and the Royal College of Ophthalmologists, 2001. 2 Friedman DS, Reeves SW, Bass EB, Lubomski LH, Fleisher LA, Schein OD. Patient preferences for anaesthesia management during cataract surgery. Br J Ophthalmol 2004; 88: 333e5. 3 Tan CS, Au Eong KG, Kumar CM. Visual experiences during cataract surgery: what anaesthesia providers should know. Eur J Anaesthesiol 2005; 22: 413e9. 4 Zafirakis P, Voudouri A, Rowe S, et al. Topical versus sub-Tenon’s anaesthesia without sedation in cataract surgery. J Cataract Refract Surg 2001; 27: 873e9. 5 Srinivasan S, Fern AI, Selvaraj S, Hasan S. Randomized doubleblind clinical trial comparing topical and sub-Tenon’s anaesthesia in routine cataract surgery. Br J Anaesth 2004; 93: 683e6.

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Ocular anatomy and physiology relevant to anaesthesia

Learning objectives After reading this article, you should be able to: C describe the fundamental anatomy of the orbit and understand its relevance to eye blocks C draw a labelled schematic diagram of the eyeball and anterior segment C understand basic optics, common visual defects and optic neural pathways.

Andrew Presland John Myatt

Abstract The orbit contains many delicate and vulnerable structures, but with a solid knowledge of the anatomy one can minimize the chance of complications and better understand how regional blocks work. This article discusses anatomy of the orbit and eye, and includes rudimentary ocular physiology.

Orbital blowout fractures Blunt trauma to the eyeball may result in a blowout fracture. This occurs most commonly on the relatively thin orbital floor. Inferior rectus sometimes becomes incarcerated with inferior blowout fractures and this may cause diplopia or (especially in children) fainting due to activation of the oculocardiac reflex.

Keywords Aqueous humour; iris; pupil; retina; Tenon’s fascia; vitreous body

holes (fissures and foramina) allow the passage of nerves and blood vessels between the cranial fossae and the orbital cavity (Figure 3). The inside of the orbital cavity is lined with a loosely attached fascial layer of periosteum. This layer is continuous anteriorly

The bony orbit Shape and structure The best way to understand the three-dimensional shape of the orbit is to look at a skull. It can be thought of as a socket in the skull that would accommodate a short ice-cream cone, with the tip innermost. How each orbit relates to the other can be seen by placing two ice-cream cones side by side. The volume of each orbit is around 30 ml, but varies between individuals. Medial to each orbital cavity lies the nasal cavity. The angle described by the medial and lateral walls from the posteriorly situated optic foramen is roughly 45 degrees, but can vary between about 40 and 60 degrees (Figures 1 and 2). The orbit has a roof, a floor, and medial and lateral walls. It is made up of frontal, zygomatic, sphenoid, ethmoid, lacrimal and maxillary bones (Figure 3). Superiorly, the orbital margin has a notch (which can be palpated at about 2.0e2.5 cm from the medial wall) that carries the supraorbital nerve. On the lateral orbital margin the notch formed by the suture line of the frontal and zygomatic bones can be palpated.

Long axis of muscle cone

22.5˚

Optic nerves

45˚

90˚

Periosteum and foramina There are a number of holes in the orbit, the biggest of which is at the front where the eyeball sits. At the back of the orbit the

Andrew Presland FRCA is Consultant Anaesthetist for adults and children at Moorfields Eye Hospital NHS Trust, London, UK. He graduated from the Royal Free Hospital School of Medicine, London University in 1992, and trained in anaesthetics at the North London (Central) School. Conflicts of interest: none declared. John Myatt FRCA is a Specialist Registrar in Anaesthesia on the Imperial School (Northwest Thames) rotation. He graduated from Imperial College School of Medicine in 2000. Conflicts of interest: none declared.

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Figure 1 Geometry of the bony orbit.

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Muscles and nerves of the orbit Trochlea

Levator palpebrae superioris

Infratrochlear nerve Anterior ethmoidal nerve

Superior rectus Lacrimal gland Lateral rectus

Superior oblique

Lacrimal nerves

Medial rectus

Short ciliary nerve Ciliary ganglion Abducent nerve

Long ciliary nerves Trochlear nerve Optic nerve

Superior rectus

Nasociliary nerve Oculomotor nerve, superior division

Levator palpebrae superioris

Figure 2

with the external periosteum of the skull and within the cranium with the dura mater.

The recti (superior, inferior, medial and lateral) arise from a ring-shaped thickening of periosteum surrounding the optic canal (Figure 3). They pass forward, getting wider as they do so, to attach onto the surface of the globe anterior to the coronal equator of the eyeball. These four muscles form the ‘muscle cone’ (or simply ‘the cone’). The distinction between intraconal and extraconal is important to anaesthetists when performing regional blocks (Table 1).

Orbital contents Muscles and their nerve supply There are four rectus muscles, two oblique muscles and a levator palpebrae superioris muscle situated within each orbit.

Bones of the orbit (left); extraocular muscle attachments and nerve supply (right) Supratrochlear nerve Levator palpebrae superioris Supraorbital nerve Superior rectus Ophthalmic vein Lacrimal nerve

Orbital plate of frontal Superior orbital fissure Zygomatic Greater wing of sphenoid

Frontal nerve Trochlear nerve Upper division of oculormotor nerve Inferior orbital fissure Abducent Nasociliary Lower division of oculomotor nerve

Optic canal Lesser wing of sphenoid Maxilla Ethmoid Lacrimal Superior oblique

Ophthalmic artery Inferior rectus Optic nerve

Medial rectus Reproduced with permission from Snell RS. Clinical anatomy by systems. Philadelphia: Lippincott, Williams and Wilkins, 2007

Figure 3

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the sclera at the corneoscleral junction (limbus). From its origin, Tenon’s fascia is adherent to the overlying conjunctiva but as it passes backwards and continues closely overlying the sclera, the two layers separate. The conjunctiva also arises at the limbus but is reflected onto the inner surface of the eyelids and does not continue posteriorly within the orbit. Between Tenon’s fascia and the sclera is a potential space, called the sub-Tenon’s space.

Eye blocks Block Site of anaesthetic delivery Notes Retrobulbar Intraconal Rapid onset Peribulbar Extraconal Relies on spread into cone Delayed onset Sub-Tenon’s Sub-Tenon’s space Often spreads into cone Rapid onset

The eyeball The eyeball is made up of three main layers: a fibrous exterior layer, a vascular/muscular layer and a neural layer (Figure 4). The outermost fibrous layer comprises the sclera (or white of the eye) and the clear cornea. This layer is made up of collagen and elastin. The composition of the sclera and cornea is identical; however, one layer is clear and the other opaque. This is because of the structural organization of the collagen fibres: in the cornea, collagen fibres are arranged in highly regular laminae; in the sclera, the fibres appear interwoven and extend in all directions. If the fibrous layer of the eye is broken, there is said to be a penetrating eye injury (Table 2). There is a high risk of subsequent visual loss through expulsion of the contents of the eye, retinal detachment or infection. Inside the fibrous layer is the vascular/muscular layer. Posteriorly is the choroid (Figure 4). Richly vascular, the choroid supplies oxygen and nutrients to outer layers of the retina and the structures of the anterior chamber. It is loosely adherent to the sclera. Anteriorly the choroid becomes continuous with the ciliary body, which, in turn, is continuous with the iris.

Table 1

A retrobulbar block aims to deliver local anaesthetic within the muscle cone and close to the nerves, and works instantly. A peribulbar block delivers local anaesthetic outside the cone and relies on spread of anaesthetic to within the cone. Hence, the block takes several minutes to develop fully and requires a greater injectate volume. A sub-Tenon’s block achieves anaesthesia within the sub-Tenon’s space (described below), but local anaesthetic often spills into the cone. The superior, inferior and medial recti, and the inferior oblique muscles are all supplied by the oculomotor nerve (III cranial nerve). The lateral rectus is supplied by the abducent nerve (VI cranial nerve). These nerves all reside within the cone. The inferior oblique muscle arises close to the nasolacrimal canal on the floor of the orbit. It passes backwards and laterally beneath the inferior rectus and rises to insert below the belly of the lateral rectus in a broad tendon behind the coronal equator of the eyeball. The superior oblique muscle arises from the body of the sphenoid, close to the origin of the recti. As it passes forward it becomes rounded and tendinous and loops through the fibrocartilagenous trochlea, which is medial to the supraorbital notch just inside the orbital rim. It then passes backwards and laterally and inserts onto the sclera beneath the superior rectus muscle and behind the coronal equator of the eyeball. The superior oblique muscle is supplied by the trochlear nerve (IV cranial nerve) which is situated outside the muscle cone (Figure 3). Commonly with retrobulbar and sub-Tenon’s blocks the trochlear nerve is spared, leading to some remaining rotational movement of the eyeball.

Anatomy of the eyeball Vitreous Lens

Sclera

Iris Pupil Cornea

Ocular movement The long axis of the muscle cone (and orbit) is approximately 22.5 degrees (45/2) from the sagittal plane. It is useful to remember this when thinking about the action of the muscles (Figure 1). Medial and lateral rectus muscles move the eye to the left and right. The superior and inferior recti do not move the eye ‘straight’ up and down, owing to the 22.5 degree angle of the long axis of the cone. The action of looking straight up and down is a complex interaction of the recti and other extraocular muscles.

Anterior chamber

Choroid Retina

Optic nerve Optic disc

Ciliary body

Tenon’s fascia and the conjunctiva Tenon’s fascia is a layer of connective tissue that envelops the eyeball, and is pierced by the muscles and nerves that penetrate and attach to it. It is not present over the cornea but arises from

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Extraocular muscle

Posterior chamber

Macula Blood vessels of the retina

Figure 4

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the eye (the optic disc seen at retinoscopy). This results in a small blind spot on the retina. At the posterior pole of the eye, medial to the optic disc, the macula lutea (yellow spot) can be seen. This is the position of the fovea, a small area where the colour photoreceptors (cones) are intensely concentrated. The fovea is the point of greatest visual acuity, where light rays are concentrated when fixing on an object.

Penetrating eye injury Causes Management Complications

Fibrous layer of eye disrupted by sharp object, high velocity missile or blunt trauma Surgery, antibiotics Prolapse of eye contents, infection, cataract, retinal detachment, visual loss

The chambers of the eye and the lens Table 2

Within the eyeball are two ‘fluid’ media: the aqueous humour and vitreous body. They are separated by the lens and its suspensory ligament. The aqueous humour, as its name suggests, is a watery substance. It is secreted by the ciliary processes into the posterior chamber, which is anterior to the lens but behind the iris. The anterior chamber lies anterior to the iris and behind the cornea (Figure 5). In the angle between the cornea and iris lies the trabecular meshwork. This is not normally visible to the naked eye but contains the canal of Schlemm, into which the aqueous humour drains and is removed. Glaucoma is a condition in which there is reduced drainage of aqueous humour. This results in rising intraocular pressure causing damage to the optic nerve. The vitreous body is a gelatinous substance that gives the eye structural support. It lies behind the lens and fills the bulk of the space within the globe. The vitreous may be removed during repair of retinal detachment (vitrectomy e see Table 3). The lens is clear, biconvex in shape and is contained within an elastic capsule. It is attached to the ciliary body by the suspensory ligament (zonules). The lens has no blood supply but receives nutrients from the aqueous humour. A cataract occurs when opacity develops within the lens.

The ciliary body is made up of ciliary muscle, which controls the shape of the lens (accommodation, discussed below), and the ciliary processes, which produce aqueous humour (Figure 5). The iris is the ring-shaped, muscular, coloured part of the eye. At the edges of the ring are longitudinal muscle fibres, which cause the pupil to dilate when they contract. ‘Dilator pupillae’ is supplied by postganglionic sympathetic nerve fibres originating in the cervical plexus. The innermost portion of the iris comprises the circular sphincter muscle fibres, which cause pupillary constriction. ‘Sphincter pupillae’ is supplied by postganglionic parasympathetic nerve fibres originating in the ciliary ganglion. The innermost layer of the eyeball is the neural layer, or retina. The retina has many layers of cells, and contains the lightsensitive photoreceptors, the rods and cones, which detect light impulses from the environment and relay them to the visual cortex. There are no photoreceptors where the optic nerve enters

Blood supply to the eye The ophthalmic artery is a branch of the internal carotid artery. It enters the orbit through the optic canal alongside the optic nerve, and its branches supply the eyeball and extraocular muscles (Figure 6a and b). The most clinically significant branch of the ophthalmic artery is the central retinal artery, which pierces the dural coat of the

Vitrectomy Definition

Indicated during treatment of

Complications

Figure 5

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Surgery to repair retinal detachment, and to prevent further detachment and visual loss. Vitreous is removed to facilitate access to the retina Vitreous floaters obscuring vision Retinal detachment Epiretinal membranes Diabetic retinopathy (bleeding/retinal detachment/scar tissue) Macular holes Vitreous haemorrhage Retinal detachment, infection, bleeding, cataract

Table 3

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optic nerve and travels within the nerve itself. It supplies the innermost layer of the retina and is an end-artery. Branches of the central retinal artery may be viewed radiating out from the optic disc at fundoscopy.

Central retinal artery occlusion Because the terminal branches of the central retinal artery are end arteries, obstruction by an embolus results in sudden onset blindness in the affected area of usually only one eye.

Central retinal vein occlusion Thrombophelebitis of the cavernous sinus or central retinal vein can result in blockage of the small retinal veins, usually resulting in slow, painless loss of vision.

The superior and inferior ophthalmic veins collect blood from the structures within the orbit. They exit the orbit via the superior orbital fissure and empty into the cavernous sinus.

Essential ocular physiology Basic optics When parallel light rays from a distant object enter the eye they are refracted (bent), inverted and directed onto the retina. Emmetropia or normal vision occurs if a focused image forms on the retina without the aid of glasses or contact lenses. If an individual’s gaze moves from a distant object to a close object the light rays must be bent further in order to produce a focused image. In humans this is achieved by contraction of the ciliary muscle which causes the lens to become more rounded. This increases the refractive power of the lens and is called accommodation. In myopia (short sight) the eyeball is too long and the refracted image focuses in front of the retina. Myopia is corrected by wearing biconcave lenses. People with myopia can usually see nearby objects unaided. In hyperopia (long sight) the eyeball is too short and the refracted image focuses behind the retina. People with hyperopia can see distant objects clearly by the mechanism of accommodation. However, this may result in eye strain if the vision remains uncorrected. The optical solution is to wear a biconvex lens (Table 4). With age the lens becomes less elastic and accommodation causes less change in the curvature of the lens. This in turn

Figure 6

Common visual defects and their correction Condition Emmetropia Myopia Hyperopia Presbyopia Pseudophakic eyes

Image focus On retina In front of retina Behind retina Behind retina No accommodation

Common term Normal vision Short sight. Can usually see nearby objects unaided Long sight. Can usually see distant objects unaided ‘Old sight’ (near objects only) Can see distant objects unaided, usually need reading glasses

Corrective lens No correction Concave Biconvex Convex Convex

Table 4

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vice versa (Figure 7). The neural pathway continues posteriorly to the geniculate body of the thalamus and on to the visual cortex in the occipital lobe.

Visual neural pathway Left eye Left field

Right eye Right field

Lesions of the visual pathways and visual field defects

Retina Optic nerve

The anatomical arrangement of the visual pathways leads to specific visual field loss patterns determined by the site of a lesion. Optic nerve lesions can lead to scotomas or complete blindness in the affected eye. Bitemporal hemianopia (loss of temporal field of vision in right and left visual fields) can be produced by a lesion at the optic chiasm. Homonymous hemianopia (loss of either right or left field of vision) can be produced by a lesion at the optic tract, optic radiation or visual cortex.

Short ciliary nerves Ciliary ganglion Optic tract Lateral geniculate nucleus of thalalmus Edinger-Westphal nuclei

Optic radiation

Pupillary reflexes When we shine a bright light into the eye the pupil constricts. This is known as the pupillary light reflex. Normally, the opposite pupil also constricts. This is the consensual light reflex. The afferent neurones involved in the integrity of this reflex travel in the optic nerve to the lateral geniculate body of the thalamus. Impulses then pass into the midbrain, deviating from the bulk sensory afferents. Fibres from the midbrain pass to both the ipsilateral and contralateral EdingereWestphal nuclei, and efferent neurones return via the ciliary body to cause pupillary constriction. Lesions at any point along the pathway may result in loss of or anomalous reflexes (Figure 7). A

Visual cortex

Figure 7

means that the nearest point we can focus clearly on moves gradually further from the eye with time. This condition is called presbyopia or ‘old sight’ and is the reason why many older people eventually need to wear glasses with a convex lens for reading and close work. In pseudophakic eyes (i.e. when a lens prosthesis is in place) accommodation is not possible. It is usual to require reading glasses for close work in this situation too.

FURTHER READING Ganong WF. Review of medical physiology. 21st edn. New York: McGrawHill, 2003. Hamilton RC. Techniques of orbital regional anaesthesia. Br J Anaesthesia 1995; 75: 88e92. Johnson RW. Anatomy for ophthalmic anaesthetists. Br J Anaesthesia 1995; 75: 80e7. Romanes GJ. Cunningham’s manual of practical anatomy. 15th edn. Oxford: Oxford University Press, 1986.

Neural pathways Light in the visible spectrum is converted into action potentials by the rod and cone cells. These action potentials are relayed back to the optic nerve and pass back to the optic chiasm. At the optic chiasm impulses from the nasal side of the retina decussate, while impulses from the temporal retina remain ipsilateral. In the optic tract the impulses are generated by each hemi-field; hence the left optic tract carries the image from the right visual field and

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