Anaesthesia, 1998, 53, pages 157–161 ................................................................................................................................................................................................................................................

R E V I E W A RT I C L E

The aetiology and prevention of peri-operative corneal abrasions E. White1 and M. M. Crosse2 1 Senior Registrar and 2 Consultant, Shackleton Department of Anaesthesia, Southampton General Hospital, Southampton SO16 6YD, UK Summary

Corneal abrasion is the most frequent ocular complication to occur during the peri-operative period. This review describes the aetiology of corneal abrasions and evaluates the current methods of prevention. Most abrasions are caused by lagophthalmos (failure of the eyelids to close fully) during general anaesthesia, resulting in corneal drying. General anaesthesia reduces both the production and the stability of tears and therefore increases the incidence of this painful condition. Taping the eyelids closed, soft contact lenses, the instillation of aqueous gels or paraffin-based ointments are all effective in preventing corneal abrasions, but ointments are associated with significant morbidity. Keywords Eye; cornea. Complications; corneal abrasion. Anaesthesia; general. ...................................................................................... Correspondence to: Dr Emert White Accepted: 23 June 1997

The most frequent ocular complication of general anaesthesia is corneal abrasion [1]. In the most recent American Society of Anesthesiologists’ closed claims analysis of ocular injuries associated with general anaesthesia, 35% were corneal abrasions, of which 16% resulted in permanent ocular damage [2]. Corneal abrasions may be the cause of great pain and distress in the postoperative period and preventive measures should be taken. Various methods of protecting the eye during general anaesthesia for nonophthalmic surgery have been recommended but there have been few studies which compare the efficacy of accepted eye protection strategies. Anatomy of the cornea

The cornea forms the anterior one-sixth of the outer coat of the eyeball [3]. It is composed of five layers and is 1.5 mm thick at its centre and 1 mm thick at the periphery. The external surface is a layer of delicate epithelium which is continuous with the conjunctiva. The cornea is avascular. The central portion is oxygenated indirectly from atmospheric oxygen dissolved in the precorneal tear film, while the periphery receives oxygen from the anterior ciliary blood vessels. Q 1998 Blackwell Science Ltd

The cornea is protected by a precorneal tear film which consists of three layers; lipid, aqueous and mucin. The outermost layer consists of the oily secretions from the meibomian glands and the glands of Zeis. The functions of this lipid layer are to prevent the evaporation of the underlying aqueous layer, to increase the surface tension hence preventing the overflow of tears over the eyelid and to act as a lubricant for the eyelids. The middle aqueous layer is secreted by the main and accessory lacrimal glands. Its functions are to supply atmospheric oxygen to the corneal epithelium, provide a smooth optical surface, irrigate the cornea of debris and provide a host defence mechanism with immunoglobulins A and G, complement factors and lysozymes that are contained in the aqueous layer [4]. Hence a dry eye is more susceptible to infection. The inner mucin layer is secreted by goblet cells in the conjunctiva, crypts of Henle and glands of Manz. Its main function is to convert the corneal epithelium from a hydrophobic to a hydrophilic surface. The precorneal tear film varies in thickness and is regenerated by blinking. Two seconds after blinking it measures 8.7 mm whilst 30 seconds after blinking it measures 4.5 mm [5]. 157

E. White and M. M. Crosse • Peri-operative corneal abrasions Anaesthesia, 1998, 53, pages 157–161 ................................................................................................................................................................................................................................................

Mechanisms of corneal injuries

During the peri-operative period 20% of corneal abrasions occur as a result of direct trauma or chemical injury, but the majority are associated with lagophthalmos (failure of the eyelids to close properly) leading to corneal drying [2]. The eye may be injured by face-masks, the anaesthetist’s hands, watch strap, name badge and laryngoscope during intubation, surgical drapes, surgical instruments, skin preparation solutions, or the direct irritant effect of inhalational anaesthetic agents [1, 6]. In the postoperative recovery period the eye may be injured by face masks, the patient’s fingers or the bed linen, especially if the patient is in the lateral position [2, 7, 8]. The superior aspect of the cornea is usually covered by the upper eyelid and exists in an environment of chronic hypoxia. The mean percentage of oxygen available at the superior corneal surface is 10.4% for the open-eye and 6.6% for the closed-eye, compared with 20.9% and 7.7% for the central cornea under similar conditions. The cornea is extremely sensitive to a lack of oxygen. The times taken for the partial pressure of oxygen to decrease from 18.2 kPa to 5.3 kPa in the superior, inferior and central parts of the cornea when exposed to a hypoxic environment are 27, 25 and 22 s, respectively [9]. Pressure applied to the globe of the eye, for example from an ill fitting face-mask, will reduce choroidal blood flow and hence oxygen delivery to the peripheral cornea [10]. Inadequate supply of oxygen to the cornea produces oedema and in the presence of a dry environment desquamation of the epithelial layer readily occurs producing an abrasion. Corneal oedema may also occur as a result of decreased venous return and raised intra-ocular pressure secondary to tracheal intubation, positive pressure ventilation or poor head positioning [11]. During normal sleep, lid closure is maintained by the tonic contractions of the orbicularis muscle [12]. Lagophthalmos only occurs in 4.6% of individuals [13]. However, under anaesthesia one study demonstrated that 59% of patients failed to have complete eyelid closure [6]. Bell’s phenomenon, in which the eyeball turns upward during sleep, hence protecting the cornea, occurs in 42% of healthy individuals [14], but is abolished by general anaesthesia, as is the blink reflex which regenerates the tear film. General anaesthesia significantly reduces both tear production [15, 16] and stability [17], predisposing to corneal drying and abrasion. The precorneal tear film ruptures in the event of the eyelids remaining open, leaving dry patches on the cornea. The time taken for this film to rupture is known as the break-up time and is dependent on the viscosity of the precorneal tear film [18]. The normal 158

break-up time is 36.4 6 4.2 s. General anaesthesia reduces the break-up time of the precorneal tear film (Fig. 1) by depressing the secretion of the aqueous component of the tear film by the lacrimal glands. In a series of 20 patients Krupin et al. [16] using the Schirmer test demonstrated a decrease in basal tear production from 13.6 6 1.9 mm per 5 min (mean 6 SEM) to 3.6 6 1.1 mm per 5 min, 10 min after induction of anaesthesia. Tear production was further decreased at 30 min (0.60 6 0.3) and 60 min (0.9 6 0.5). The decreases were highly significant (p < 0.001). Premedication with atropine did not significantly reduce tear production. With the aid of a slit lamp following instillation of fluorescein, Hrazdirova et al. continuously monitored the exposed corneas of patients undergoing elective general anaesthesia of 60–390 min duration [17]. Corneal changes started to occur after a duration of 100 min of anaesthesia always beginning in the lower half of the cornea. In some eyes erosions occurred after 2 h of anaesthesia. These findings are supported by Batra and Bali [6] who also

Figure 1 The effect of duration of general anaesthesia (hours) on the mean break-up time (seconds) of precorneal tear film. Reproduced with permission from Hrazdirova and co-workers 1990 [17].

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Anaesthesia, 1998, 53, pages 157–161 E. White and M. M. Crosse • Peri-operative corneal abrasions ................................................................................................................................................................................................................................................

Figure 2 Distribution of cases showing positive fluorescein

staining in relation to duration of anaesthesia. Reproduced with permission from Batra and Bali 1977 [6].

failed to detect any corneal abrasions in patients undergoing anaesthesia of less than 1 h duration and found a peak incidence of corneal abrasions occurring between 90 and 150 min of anaesthesia (Fig. 2). Strategies for eye protection

Few studies have been done to elucidate the best method of protecting the eye during general anaesthesia. Various strategies for peri-operative protection of eyes have been suggested. Methods recommended include simple manual closure of the eyelids, taping the eyelids closed, installation of paraffin-based ointments into the conjunctival sac, instillation of aqueous solutions, or viscous gels into the eye and the insertion of hydrophilic contact lenses. Traditionally, ointments have been preferred because they are retained longer in the eye. The half-lives in the closed nonblinking human eye of paraffin-based ointments, methylcellulose and saline are 32, 12 and 6.6 min, respectively, [19]. In practice, repeat installation of ointments is only required every 90 min because of decreased tear production during anaesthesia [15]. Methylcellulose solutions increase the stability of the precorneal film prolonging the break-up time, whereas paraffin-based ointments reduce the break-up time [20]. In a study of 13 different artificial tears, Lemp et al. [21] found a duration of action between 45 and 115 min using the time taken for the break-up time to return to its normal value as the parameter of measurement. Batra and Bali [6] studied 200 healthy patients undergoing elective general anaesthesia. They were randomly allocated into two equal groups of 100 patients. In one group no protective measures were taken. They found a Q 1998 Blackwell Science Ltd

44% incidence of corneal abrasions in 59 patients with lagophthalmos. In the second group the eyes were either taped closed (75 patients) or protected with vaseline gauze (25 patients). No corneal abrasions were found in the patients whose eyes were either taped closed, received vaseline gauze or whose eyes closed naturally. In a double-blind trial, 47 patients undergoing elective general anaesthesia of less than 90 min duration were given eye protection with a paraffin-based ointment in one eye and 4% methylcellulose in the other [22]. One patient who received 4% methylcellulose had a corneal abrasion. In a similar study, Boggild-Madsen and co-workers [23] randomly allocated 120 patients undergoing general anaesthesia of more than 90 min duration to receive a paraffinbased ointment in one eye and 4% methylcellulose in the other. There were virtually no complications in the methylcellulose group, but a significant amount of eyelid oedema, conjunctival erythema and complaints of blurred vision in the ointment group, especially in those patients who received halothane. Halothane does not normally irritate mucous membranes. However, halothane is 40 times more soluble in paraffin-based products than in water-based products such as methylcellulose. It is therefore possible that in the presence of a paraffin-based ointment sufficiently high concentrations of halothane occurred resulting in inflammation of the eye [24]. Siffring and Poulton [25] studied 127 patients undergoing elective general anaesthesia of between 30 and 180 min duration. Patients were randomly assigned to one of four groups; Group A received Lacri-lube ointment (paraffin-based) and tape closure of their eyes; Group B Duratears ointment (paraffin-based) and tape closure of their eyes; Group C methylcellulose drops (water-based) and tape closure of their eyes and Group D hypoallergenic paper tape closure of their eyes alone. No corneal abrasions were detected in any of the patients studied. However, the morbidity of the patients in groups A and B were significantly increased when compared with patients in groups C and D. Seventy-five per cent of patients in Group A and 55% of patients in group B complained of blurred vision for an average of 7.4 and 4.7 h, respectively, associated with a significant reduction in visual acuity. In addition 62.5% of patients in Group A and 42% of patients in Group B complained of a sensation of something in their eyes which persisted for an average of 5.2 and 3.5 h, respectively. Twenty per cent of the patients treated with Duratears, which contains the allergen methylparaben, had scleral erythema. In contrast, only one patient randomly allocated to receive methylcellulose complained of blurred vision and of a sensation of something in their eyes. Patients randomly allocated to have their eyes taped had no morbidity. 159

E. White and M. M. Crosse • Peri-operative corneal abrasions Anaesthesia, 1998, 53, pages 157–161 ................................................................................................................................................................................................................................................

Cucchiara and Black [26] studied 4652 patients undergoing neurosurgical procedures over a 13-month period. All patients had their eyes taped closed after tracheal intubation. Eye ointment was given to 2439 patients. Eight patients (0.17%), four in the ointment group and four in the no-ointment group, developed corneal abrasions. Five corneal abrasions occurred in the 681 patients (0.73%) who underwent lumbar laminectomy while prone with the head turned to the side. The abrasions always occurred in the lower eye. Marquardt et al. [27] studied 30 patients undergoing ENT procedures of 20–510 min duration. Dexpanthenolbased ointment was placed in the right eye and Visidic (a clear viscous artificial tear solution) in the left at hourly intervals. Tear production in both groups was similar before and after operation. The break-up time of the precorneal film was prolonged in the eyes given Visidic from a mean of 15.7 s before operation to 22.6 s after operation. It was shortened with eyes given dexpanthenolbased ointment from 16.0 s before operation to 13.9 s after operation. Ten per cent of patients who received Visidic complained of discomfort compared with 30% of those who were given dexpanthenol. Hrazdirova et al. [1] studied 100 healthy patients undergoing surgery of 60–390 min duration. They placed a hydrophilic contact lens in one eye and the other eye remained unprotected. Tear production was measured in both eyes every 15 min using the Schirmer test. Tear production was reduced in both groups (Fig. 3) but was greater in the contact lens group at all times. They concluded that hydrophilic contact lenses had a similar efficacy to paraffin-based ointments in preventing corneal abrasions during general anaesthesia. However, they acknowledged the practical difficulties associated with their use. Discussion

General anaesthesia reduces tear production and stability, increases the frequency of lagophthalmos, abolishes the blink reflex and inhibits Bell’s phenomenon. Most corneal abrasions occur during the peri-operative period because of lagophthalmos resulting in exposure and drying of the cornea. Patients at greatest risks for peri-operative corneal abrasions are those who require surgical procedures, in the prone position, on the head and neck and of greater than 90 min duration. We do not recommend the routine instillation of aqueous solutions, viscous gels and ointments during the peri-operative period. They do not offer sufficient additional protection against the development of corneal abrasions and ointments in particular contribute to significant ocular morbidity. Transparent aqueous solutions or viscous gels may offer additional protection for those anaesthetists who frequently open their patient’s 160

Figure 3 The effect of duration of general anaesthesia on mean

tear production using the Schirmer test (mm of wetting of a strip of filter paper in 5 min). (—) Unprotected eye; (- - -) soft contact lens.

eyelids to assess the degree of pupillary dilatation. They should be instilled at least by hourly intervals. We recommend that all patients should have their eyes taped closed immediately after pre-oxygenation and intravenous induction of anaesthesia except during rapid sequence intubation, when securing the airway takes precedence over eye protection. Patients who are to undergo anaesthesia in the prone position should have their eyes taped and their heads maintained in a neutral position avoiding pressure on their eyes. Turning the head to one side in the prone position decreases the venous return from the head and raises the intra-ocular pressure in the lower eye, which may result in corneal oedema and ultimately abrasion. Above all, the anaesthetist should be aware of the causes of eye damage and personally take responsibility for the protective measures. Acknowledgments

The help given by Dr M. Lesna, consultant histopathologist and Dr H. Ocker, senior house officer in anaesthetics Q 1998 Blackwell Science Ltd

Anaesthesia, 1998, 53, pages 157–161 E. White and M. M. Crosse • Peri-operative corneal abrasions ................................................................................................................................................................................................................................................

at The Royal Bournemouth Hospital, in the translation of foreign articles is gratefully acknowledged. We would also like to thank the Department of Teaching Media, University of Southampton, for their help with producing the illustrations.

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The aetiology and prevention of peri-operative ... - Wiley Online Library

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