Download The aetiology and prevention of peri-operative

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