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Ophthalmic Anaesthesia
Chapter · October 2013
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Smith and Aitkenhead's Textbook of Anaesthesia, Sixth Edition
Alan R. Aitkenhead, Iain K. Moppett, and Jonathan P. Thompson
31, 620-639, © 2013, Elsevier Limited. All rights reserved.
OPHTHALMIC ANAESTHESIA
Professor Chandra M Kumar (Singapore) & Dr Sean Williamson (UK)
P atients who present for eye surgery are frequently at the extremes of age. Neonatal and geriatric
a­ naesthesia both present special problems. Some eye
­surgery may last many hours and repeated anaesthetics at short intervals are often necessary. The anaesthetic technique may influence intraocular pressure
(IOP), and skilled administration of either local or
­general anaesthesia contributes directly to the successful ­outcome of the surgery. Close co-operation
and clear understanding between surgeon and anaesthetist are essential. Risks and benefits must be assessed carefully and the anaesthetic technique selected
accordingly.
Ophthalmic surgery can be classified into subspecialties and intraocular or extraocular procedures may
be performed (Table 30.1); each has different anaesthetic requirements.
PHYSIOLOGY OF THE EYE
The perception of light requires function of both the
eye and its central nervous system connections. The
protective homeostatic mechanisms of the eye are interfered with by anaesthesia in a similar way to the
effects of anaesthesia on the central nervous system. The sclera and its contents are analogous to
the skull and its contents. There is a similar elastance curve, but for slightly different reasons. This
is due to the sclera being an elastic but completely
full container unlike the rigid, but slightly empty,
cranium which has some room for expansion of its
contents.
TA B L E 3 0 .1
Categorization of Ophthalmic Surgery
Ophthalmology Subspecialities
Paediatric
Oculoplastic
Vitreoretinal
Anterior segment
Glaucoma
Neuro-ophthalmology
Extraocular Operations
Globe and orbit
Eyebrow and eyelid
Lacrimal system
Muscles
Conjunctiva
Cornea, surface
Intraocular Operations
Iris and anterior chamber
Lens and cataract
Vitreous
Retina
Cornea, full thickness
Control of Intraocular Pressure
The factors controlling IOP are very complex and include external pressure, volume of the arterial and venous vasculature (choroidal volume) and the volumes
of the aqueous and vitreous humour.
Intraocular pressure depends on the rigidity of the
sclera as well as any external pressure. Functionally, it
is a balance between the production and removal of
aqueous humour (approximately 2.5 μL min−1). Factors
which affect IOP are shown in Table 30.2. Chronic
changes in IOP (normally 10–25 mmHg (mean 15)),
601
602
30  OPHTHALMIC ANAESTHESIA
either upwards or downwards cause structural effects
and loss of function. There is a relationship between increasing axial length and increasing IOP. Low p
­ ressure
results in blood–aqueous barrier breakdown, cataract,
macular oedema and papilloedema. High pressure
causes iris sphincter paralysis, iris atrophy, lens opacities and optic nerve atrophy.
Pressure is distributed evenly throughout the eye
and the pressure is generally the same in the posterior vitreous body as it is in the aqueous humour,
despite the fact that the pressure is generated in the
anterior segment. Each eye may have a different pressure. The aqueous is produced by an active secretory
process in the non-pigmented epithelium of the ciliary
body. Large molecules are excluded by the so-called
blood–aqueous barrier between the epithelium and
iris capillaries. The Na+/K+ ATPase pump is involved
in the active transport of sodium into the aqueous.
Carbonic anhydrase catalyses the conversion of water
and ­carbon dioxide to carbonic acid, which passes passively into the aqueous. Acetazolamide, an inhibitor
of carbonic anhydrase used in the treatment of raised
IOP, reduces bicarbonate and sodium transport into
the aqueous to produce its therapeutic effect.
In addition to this active secretory production, there
is a less important hydrostatic element dependent on
ocular perfusion pressure. The ciliary body is highly
vascular and supplied directly by the ciliary ­arteries.
Aqueous production is related linearly to blood flow.
Flow and vascular pressure are controlled by the
­autonomic nervous system and autoregulation exists,
similar to cerebral blood flow. Aqueous removal is inhibited by pressure within the pars plana, and e­ piscleral
venules restrict the vascular outflow, as does the IOP.
The aqueous flows from the ciliary body through
the trabecular meshwork into the anterior chamber before exiting through the angle of Schlemm
(Fig. 30.1). The sum of the hydrostatic inflow and the
active aqueous production minus the active resorption and passive filtration must equal zero to achieve
balance. Alteration of any individual feature can lead
to changes in IOP.
TA B L E 3 0 . 2
Factors Which Affect Intraocular Pressure (IOP)
IOP
Increase IOP
Decrease IOP
Systemic
Age
Large increase in blood pressure
Increased carotid blood flow
Increased central venous pressure
Valsalva manoeuvre
Carotid-cavernous fistula
Plasma hypo-osmolality
Hypercapnia
Sympathetic stimulation
Exercise
Large decrease in blood pressure
Decreased carotid blood flow
Decreased central venous pressure
Parasympathetic stimulation
Pregnancy
Hypothermia
Acidosis
Plasma hyperosmolality
Adrenalectomy
General anaesthesia
Local
Increased episcleral venous pressure
Blockage of ophthalmic vein
Blockage of trabecular meshwork
Contraction of extraocular muscles
Restricted extraocular muscle
Acute external pressure
Forced blinking
Relaxation of accommodation
Prostaglandin release (biphasic)
Hypersecretion of aqueous
Decreased episcleral venous pressure
Decreased ophthalmic artery blood flow
Prolonged external pressure
Retrobulbar anaesthesia
Ocular trauma
Intraocular surgery
Retinal detachment
Choroidal detachment
Inflammation
Prostaglandins (biphasic)
Accommodation
Increased aqueous outflow
603
PHYSIOLOGY OF THE EYE
Sclera
Choroid
Retina
Ciliary body
Central retinal
vein and artery
Conjunctiva
Optic nerve
Schlemm’s canal
Zonule
Cornea
Iris
Pia
Pupil
Corneal endothelium
Lens
CSF space
Vitreous
Dura
Lamina cribrosa
Anterior chamber
Posterior chamber
FIGURE 30.1  Cross-section through the eye and optic nerve. Arrows indicate flow of aqueous.
External Pressure
Pressure from squeezing the eyes closed or the injection of a volume of local anaesthetic into the orbit is
transmitted to the eyeball and increases the IOP.
Venous Pressure
Venous congestion increases vascular volume within
the eye and reduces aqueous drainage through the canal of Schlemm, causing an increase in IOP. During
anaesthesia, venous pressure is influenced mainly by
posture and transmitted intrathoracic pressure. A 15°
head-up tilt causes a significant decrease in IOP.
Raised arterial pressure, anxiety, restlessness, full
bladder, coughing, retching and airway obstruction
cause an increase in venous pressure which is reflected immediately in the IOP. Intermittent positive-­
pressure ventilation (IPPV) produces a small increase
in venous pressure secondary to the increase in mean
intrathoracic pressure, but is compensated for by control of arterial PCO2.
Arterial Blood Gas Tensions
Arterial PCO2 is an important determinant of choroidal vascular volume and IOP. A reduction in PaCO2
constricts the choroidal vessels and reduces IOP.
Elevation of PaCO2 results in a proportional and linear
increase in IOP. Increases in PaCO2 may also increase
central ­venous pressure. Hypoxaemia produces intraocular vasodilatation and an increase in IOP.
Arterial Pressure
Stable values of arterial pressure within the physiological range maintain normal IOP. Sudden increases in systolic arterial pressure above the normal
autoregulatory range increase choroidal blood volume
and consequently IOP. Reduction in arterial pressure
30  OPHTHALMIC ANAESTHESIA
below normal physiological levels reduces IOP, but
the ­response is unpredictable in old age when arterial
­capacitance is reduced.
Aqueous and Vitreous Volumes
A decrease in either aqueous or vitreous volume
­reduces IOP. Osmotic diuretics are sometimes used to
reduce aqueous and vitreous volume. Acetazolamide
reduces the production of aqueous.
Sodium Hyaluronate
Sodium hyaluronate is used as a soft viscous
­retractor during surgery. Sodium hyaluronate is a large-­
molecular-weight, clear viscoelastic polysaccharide. It
augments the effect of general anaesthesia by controlling
vitreous bulge and compensates for small changes in IOP.
The manufactured product is injected by the surgeon at
the time of incision and helps to maintain the shape of
the anterior chamber and the work space. Hyaluronate
with lidocaine admixture may be used when cataract surgery is conducted under topical anaesthesia.
OCULAR BLOOD FLOW
Ocular blood flow and IOP are intrinsically linked, as
are cerebral blood flow and intracranial pressure. The
control mechanisms are similar, although there are
differences in the anatomy. Ocular perfusion pressure
(OPP) equals the mean arterial pressure (MAP) minus
the intraocular pressure:
OPP = MAP − IOP
This is subject to autoregulation within the range
60 to 150 mmHg (Fig. 30.2).
OCULOCARDIAC REFLEX
The oculocardiac reflex is a triad of bradycardia, nausea and syncope. Classically precipitated by muscle
traction, it may also occur in association with stimulation of the eyelids or the orbital floor, and pressure on
the eye itself. Apnoea may also occur. The ophthalmic
division of the trigeminal nerve is the afferent limb,
passing through the reticular formation to the visceral
motor nuclei of the vagus nerve.
The risk of development of the oculocardiac r­ eflex
is highest in children undergoing squint s­urgery
and patients receiving explant surgery for retinal
Autoregulation range
Percentage of normal flow
604
100
Blood pressure
FIGURE 30.2  Auto-regulation of intraocular pressure (IOP).
detachment. Treatment requires either a cessation of
the stimulus or an appropriate dose of an anticholinergic drug such as atropine or glycopyrrolate. Some
­anaesthetists consider it mandatory to use prophylaxis against this reflex in susceptible patients, using
the same agents.
CONDITIONS FOR INTRAOCULAR
SURGERY
For most intraocular operations, the eye must be painfree and preferably immobile. Except for glaucoma
surgery, the pupil should be dilated and intraocular
pressure reduced.
Expulsive Haemorrhage
In the presence of markedly raised IOP, sudden reduction in pressure on incision of the globe may lead to
the expression of the contents. The balance between
venous and intraocular pressure is crucial. An increase
in venous pressure causes fluid to pool in the choroid
and may progress to cause rupture of the ciliary artery
with prolapse of the iris. On rare occasions, disastrous
expulsive haemorrhage may result in the loss of the entire contents of the eyeball.
Effect of Anaesthetic Drugs on Intraocular
Pressure
Premedication
Drugs used for premedication have little effect on intraocular pressure, and the commonly used anxiolytic
and antiemetic drugs may be used as preferred.
CHOICE OF ANAESTHESIA
Induction Agents
Most of the intravenous induction agents, with the
exception of ketamine, reduce intraocular pressure
­
and may be used as indicated clinically. Ketamine
should be avoided if intraocular surgery is planned.
Muscle Relaxants
Succinylcholine increases intraocular pressure, with a
maximal effect 2 min after i.v. administration, but the
pressure returns to baseline values after 5 min. This effect is thought to be caused by the increase in tone of
the extraocular muscles and intraocular vasodilatation.
Pretreatment with a small dose of a non-depolarizing
muscle relaxant does not obtund this response reliably.
The problems involved with the use of succinylcholine
in the patient with penetrating eye injury are discussed
on page 616.
Non-depolarizing muscle relaxants have no significant direct effects on IOP.
Volatile Anaesthetic Agents
All the volatile anaesthetic agents in use today decrease
intraocular pressure. Nitrous oxide has no effect on
IOP in the absence of air or a therapeutic inert gas
bubble in the globe (see below).
Opioids
Opioids cause a moderate reduction in IOP in the absence of significant ventilatory depression. They contribute to postoperative nausea and vomiting and are
not often required for postoperative analgesia following eye surgery.
CHOICE OF ANAESTHESIA
Ophthalmic surgery can be carried out under either
local or general anaesthesia provided that there is
both consent and compliance. The type of surgery,
its urgency and the age and fitness of the patient influence the choice (Table 30.3). Local anaesthesia is
preferred for older and sicker patients, because the
stress response to surgery is diminished and complications such as postoperative confusion, nausea, vomiting and urinary retention are mostly eliminated.
Younger patients may sometimes be too anxious for
local anaesthesia and are usually managed with general anaesthesia.
605
TA B L E 3 0 . 3
Preferred Anaesthetic Technique for Common
Surgical Procedures in Ophthalmology
Local Anaesthesia
Cataract
Glaucoma techniques
Minor extraocular plastic surgery
Laser dacrocystorhinostomy
Minor anterior segment procedures
Simple vitrectomies
General Anaesthesia
Paediatric surgery
Squint surgery
Major oculoplastic surgery
Dacrocystorhinostomy
Penetrating keratoplasty
Orbital trauma repair
Penetrating eye injuries
Complex vitreoretinal surgery
Risks and benefits of the available techniques
must be assessed carefully and anaesthesia selected
accordingly. There is a need to maintain homeostasis in the eye if intraocular surgery is planned. For
the purposes of patient comfort, it may also be necessary to consider the duration of the procedure and
the patient’s ability to stay immobile for a period
longer than a short cataract operation. However all
types of ophthalmic surgery have been carried out
with local anaesthesia in compliant patients, including repair of ocular trauma. As a general rule, patients who require general anaesthesia are usually
children and special needs adults, or adults scheduled to undergo potentially complex ophthalmic
surgery. It is important to understand the basic
physiology and anatomy of the eye before embarking on anaesthesia, irrespective of whether general
or local anaesthesia is chosen.
General Anaesthesia
Indications for General Anaesthesia
General anaesthesia is indicated when the patient
is unwilling or unable to tolerate local anaesthesia. The length and complexity of the operation
are important determinants. Surgical experience
and the need for education and training of medical staff in a suitable environment are also relevant
considerations.
606
30  OPHTHALMIC ANAESTHESIA
Contraindications to General Anaesthesia
Contraindications to general anaesthesia are related to
risk/benefit analysis. Cardiovascular, respiratory and
neurological diseases increase in frequency with age.
Adverse cardiac outcome, respiratory failure and postoperative cognitive dysfunction leading to admission
to a Critical Care Unit can occur after either local or
general anaesthesia. If a simple and safer anaesthetic
solution exists and the opinion of the anaesthetist is
that there is a significant risk of death or serious neurological morbidity from general anaesthesia, the balance
may shift towards local anaesthesia or cancelling surgery. There are no absolute contraindications and it is
not uncommon for patients with serious comorbidities
which cannot be improved preoperatively to say that the
risk of death associated with proceeding with surgery
and general anaesthesia is worth it when the desired
outcome is maintenance or improvement of vision.
Assessment and Preparation
Standard preoperative assessment should be carried
out for all patients irrespective of the chosen anaesthetic technique. Multiprofessional teamwork is the
norm and the Joint Royal Colleges’ guidelines offer appropriate advice. Appropriately trained nursing staff undertake pre-assessment and preoperative
preparation of most patients, under the guidance of
a lead ophthalmic anaesthetist. A thorough history is
required and, with input from the surgeon, a decision
can be made about the most appropriate choice of
anaesthetic to be offered to the patient. Investigations
should be based on the examination findings and
NICE guidance. Increasing age, comorbidity (such
as cardiorespiratory disease) and chronic drug treatments make routine investigations such as ECG, full
blood count and measurement of serum urea and
electrolyte concentrations potentially useful tests.
However, if local anaesthesia is planned, investigations are usually reserved for very specific indications.
Particular thought needs to be given to management
of patients with hypertension, ischaemic heart disease,
diabetes mellitus or chronic obstructive pulmonary
disease. It is important that the preoperative preparation includes consideration of whether the patient will
be able to lie flat for up to an hour without becoming
uncomfortable, claustrophobic, hypoxaemic or suffering ischaemic cardiac problems, or coughing.
Chronic anticoagulation presents potential complications which are more relevant to the surgeon or
those practising local anaesthesia (see below).
It is imperative to make sure that the patient understands and consents to the choice of anaesthetic
by taking part in an informed discussion. Patients
(and surgeons) often request anaesthetic choices
which appear contrary to the anaesthetic risk/benefit
assessment.
Induction of Anaesthesia
A smooth induction is the goal of all anaesthetists and
is particularly important in the ophthalmic setting.
Avoidance of coughing, straining and accidental increases in intrathoracic pressure which cause venous
congestion are important so that optimal eye conditions are maintained. The choice of induction drug is
of much less importance than how it is used. However,
propofol has a number of ideal qualities in this setting,
especially related to the ease of insertion of the laryngeal
mask airway. In equipotent doses, propofol has a greater
depressant effect on IOP than thiopental, but also causes
more hypotension. Succinylcholine, in isolation, causes
an increase in IOP due to muscular contractions and
intraocular vasodilatation but this effect is more than
balanced out by the effect of the induction agent.
Short-acting opioids such as fentanyl act synergist­
ically with the induction agent and obtund cardiovascular responses to airway manipulation.
Airway Management
Management of the airway is particularly important
in head and neck surgery. The airway may remain inaccessible throughout surgery and any need to adjust
or reposition an airway device during surgery could
cause disruption to surgery, with potentially sight-­
threatening consequences in ophthalmic surgery. Thus,
the safest option was traditionally felt to be to intubate the trachea and maintain ventilation and neuromuscular blockade throughout the operation. Topical
and intravenous lidocaine during laryngoscopy (and
during emergence) can help to reduce stimulation of
the trachea and larynx. A south-facing RAE tracheal
tube which is well stabilized with hypo-­
allergenic
tape (avoiding ties) is the best choice and, along with
mechanical ventilation, provides ideal conditions for
nearly all types of ophthalmic surgery. Guaranteed
CHOICE OF ANAESTHESIA
paralysis with the use of neuromuscular monitoring
avoids the risks of movement during surgery. However,
tracheal intubation can be associated with a risk of increasing IOP as a result of coughing and bucking during laryngoscopy, the pressor response to laryngoscopy
and intubation, laryngospasm or coughing after extubation, and postoperative nausea and vomiting related
to the use of neostigmine. All of these complications
assume much greater importance in open eye surgery.
The use of propofol followed by insertion of a
­laryngeal mask airway (LMA) has therefore become
popular, particularly for short ophthalmic procedures,
reducing many of the risks associated with tracheal intubation but carrying an additional risk that maintenance of the airway is less certain if the LMA is poorly
positioned or inadequately secured. The use of neuromuscular blockade with the LMA may aid mechanical
ventilation and tighter control of ocular physiology
but is considered by some anaesthetists as carrying a
significantly increased risk of aspiration.
Therefore a risk/benefit assessment should be made
by the anaesthetist, taking into account the relative
importance of the following factors: body mass index,
history of gastro-oesophageal reflux, hiatus hernia,
predicted ease of insertion of tube or LMA, length of
operation, open eye operation and fasting time.
Maintenance of Anaesthesia
The choice of technique for maintenance of anaesthesia is influenced by personal preference and the
method of airway management. The use of a volatile
anaesthetic agent is commonest because of familiarity, controllability and cost. Inhalational anaesthesia
causes a dose-dependent reduction in IOP. However,
virtually all sedative and hypnotic drugs reduce IOP.
There are, in practice, few clinical differences between
the effects of different volatile anaesthetic agents, or
between inhalational and intravenous anaesthesia.
The use of nitrous oxide depends on local availability of medical air and personal preference. The benefits of nitrous oxide are well known but two particular
risks must be considered in relation to ophthalmic anaesthesia: the increased risk of postoperative retching
and vomiting, and the effect on IOP when intraocular
gas mixtures are used for vitrectomy (see below).
Relative hypotension during anaesthesia combined with normoxia and normocapnia provide a
607
soft, well-perfused eye. A 15° head-up tilt may improve conditions. However, excessive hypotension may
prompt questions from the ophthalmologist because
of absence of flow in the retinal arteries during some
ocular procedures. Maintenance of an adequate blood
pressure is a greater challenge in elderly patients in the
absence of significant surgical stimulation. Avoidance
of an increased IOP is necessary to avoid loss of ocular
contents during open surgery.
The systemic physiological disturbance associated with most eye surgery is low. There is little, if
any, alteration in body fluid status and care should
be taken not to be too liberal with intravenous fluids
to avoid overloading the myocardium or inducing
urinary retention in the elderly. The elderly are also
more susceptible to the adverse effects of hypothermia
and attention should be given to maintaining body
temperature during all but very short procedures.
Appropriate measures should be taken to minimize
the risk of venous thromboembolism. Ophthalmic
surgery is performed commonly on patients with diabetes due to complications of the disease. If general
anaesthesia is required, local euglycaemia protocols
must be followed. Analgesia requirements are based
on the intraoperative use of a short-acting opioid and
paracetamol. Non-steroidal anti-inflammatory drugs
(NSAIDs) may be useful if there are no contraindications. Local anaesthesia with a longer-duration local
anaesthetic drug is particularly useful provided that
eye protection is maintained for the duration of action. It is unusual to require potent long-acting opioids and a cause for severe postoperative pain should
be sought because this can be a sign of ophthalmic
complications. Ophthalmic patients are particularly
prone to suffer from nausea and vomiting despite the
absence of long-acting opioids. Dexamethasone and
ondansetron are useful as prophylaxis.
Local Anaesthesia for Eye Surgery
An experienced ophthalmic surgery team can achieve
a safe and efficient service with prompt patient turnaround and excellent operating conditions based on
the use of local anaesthesia. However, serious complications of ophthalmic local anaesthesia can and
do occur. A detailed knowledge of the anatomy of the
eye and the relevant pharmacology is of paramount
importance.
608
30  OPHTHALMIC ANAESTHESIA
NOMENCLATURE OF BLOCKS
The terminology used for ophthalmic block varies
but the widely accepted nomenclature is based on the
anatomical location of the needle tip. The injection of
local anaesthetic agent into the muscle cone behind
the globe formed by the four rectus muscles and the
superior and inferior oblique muscles is known as intraconal (retrobulbar) block whereas in the extraconal
(peribulbar) block, the needle tip remains outside the
muscle cone. Multiple communications exist between
the two compartments and it is difficult to differentiate whether the needle is intraconal or extraconal after insertion. Injected local anaesthetic agent d
­ iffuses
easily across compartments and, depending on its
­
spread, anaesthesia and akinesia may occur. A faster
onset of akinesia suggests that the block is intraconal.
A combination of intraconal and extraconal block is
described as a combined retro–peribulbar block. In
sub-Tenon’s block, local anaesthetic agent is injected
under the Tenon’s capsule and this block is also known
as parabulbar block, pinpoint anaesthesia or medial
episcleral block.
Relevant Anatomy
The orbit is a four-sided irregular pyramid with its
apex pointing posteromedially and its base anteriorly.
The annulus of Zinn is a fibrous ring which arises from
the superior orbital fissure. Eye movements are controlled by four rectus muscles (inferior, lateral, medial
and superior), and the superior oblique and inferior
oblique muscles (Fig. 30.3). These muscles arise from
the annulus of Zinn and insert on the globe anterior to
the equator to form an incomplete cone. The distance
from annulus to inferior temporal orbital rim ranges
from 42 to 54 mm. It is very important that the needle
should not be inserted too far, close to the annulus,
where the vital nerves and vessels are tightly packed.
The optic nerve (II), oculomotor nerve (III, containing superior and inferior branches), abducent
nerve (VI), nasociliary nerve (a branch of nerve V), ciliary ganglion and vessels lie in the cone (Fig. 30.4). The
ophthalmic division of the oculomotor nerve divides
into superior and inferior branches before emerging
from the superior orbital fissure. The superior branch
supplies superior rectus and levator palpebrae superioris muscles. The inferior branch divides into three
to supply the medial rectus, the inferior rectus and the
Trochlea
Superior oblique
Superior rectus
Levator
Optic
nerve
Annulus
of Zinn
Lateral rectus
Inferior rectus
Inferior oblique
Medial
rectus
Superior
oblique
Lateral view
Superior
rectus
Lateral
rectus
Superior view
FIGURE 30.3  Extraocular muscles of the eye. See text for
­details. (Adapted from Gray, Henry. Anatomy of the human body. Lea &
Febiger, Philadelphia 1918; Bartleby.com, 2000.)
inferior oblique muscles. The abducent nerve emerges
from the superior orbital fissure beneath the inferior
branch of the oculomotor nerve to supply the lateral
rectus muscle. The trochlear nerve (IV) courses outside
the cone but then branches and enters the cone to supply the superior oblique muscle. An incomplete block
of this nerve leads to retained activity of the superior
oblique muscle and this occurs frequently. Squeezing
and closing of the eyelids are controlled by the zygomatic branch of the facial nerve (VII), which supplies
NOMENCLATURE OF BLOCKS
609
Levator palpebrae superioris m.
Superior orbital fissure
Superior rectus m.
Superior oblique m.
Lacrimal V n.
Frontal V n.
Trochlear IV n.
Medial rectus m.
Superior division
of oculomotor III n.
Optic nerve
Nasociliary V n.
Common tendinous ring
Abducent VI n.
Lateral rectus m.
Inferior rectus m.
Inferior division of III n.
FIGURE 30.4  Anatomy of the right orbit: relationship of the four rectus muscles and the apex of the cone to the orbital nerve supply.
the motor innervation to the orbicularis oculi muscle.
This nerve emerges from the foramen spinosum at the
base of the skull, anterior to the mastoid and behind
the earlobe. It passes through the parotid gland before
crossing the condyle of the mandible, and then passes
superficial to the zygoma and malar bone before its terminal fibres ramify to supply the deep surface of the
orbicularis oculi. The facial nerve also supplies secretomotor parasympathetic fibres to the lacrimal glands,
and glands of the nasal and palatine mucosa.
Tenon’s capsule or bulbar fascia is a membrane
which envelops the eyeball from the optic nerve to the
sclerocorneal junction, separating it from the orbital
fat and forming a socket in which it moves (Fig. 30.5).
The capsule originates at the limbus and extends
­posteriorly to the optic nerve and as sleeves along the
extraocular muscles. Tenon’s capsule is divided arbitrarily by the equator of the globe into anterior and
posterior ­portions. Anterior Tenon’s capsule is adherent to episcleral tissue from the limbus posteriorly for
about 5–10 mm and is fused with the intermuscular
septum of the extraocular muscles and overlying bulbar conjunctiva. The conjunctiva fuses with Tenon’s
capsule in this area and the sub-Tenon space can be accessed easily through an incision 5–10 mm behind the
­limbus. The posterior sub-­Tenon’s capsule is thinner
and passes round to the optic nerve, separating the
globe from the contents of the retrobulbar space.
Posteriorly, the sheath fuses with the openings around
the optic nerve.
Sensation to the eyeball is supplied through the
ophthalmic division of the trigeminal nerve (V). Just
before entering the orbit, it divides into three branches:
lacrimal, frontal and nasociliary. The nasociliary nerve
is sensory to the entire eyeball. It emerges through the
superior orbital fissure between the superior and inferior branches of the oculomotor nerve and passes
through the common tendinous ring. Two long ciliary
nerves give branches to the ciliary ganglion and, with
the short ciliary nerves, transmit sensation from the
cornea, iris and ciliary muscle. Some sensation from
the lateral conjunctiva is transmitted through the lacrimal nerve and from the upper palpebral conjunctiva
via the frontal nerve. Both nerves are outside the cone.
Intraoperative pain may be experienced if these nerves
are inadequately blocked.
The superomedial and superotemporal quadrants
have abundant blood vessels but the inferotemporal
and medial quadrants are relatively avascular and are
safer places to insert a needle or cannula.
To achieve adequate anaesthesia and akinesia, the
cranial and sensory nerves described above must be
610
30  OPHTHALMIC ANAESTHESIA
Levator palpebrae superioris
Superior rectus
Cornea
Optic nerve
Vitreous
Inferior rectus
Superior tarsus
Inferior tarsus
Tenon’s capsule
Sub-Tenon space
FIGURE 30.5  A sagittal section through the right orbital cavity, showing Tenon’s capsule and the sub-Tenon space. (Adapted
from Gray, Henry. Anatomy of the human body. Lea & Febiger, Philadelphia 1918; Bartleby.com, 2000.)
blocked. However, it is very difficult to target these
nerves individually and an adequate volume of local
anaesthetic should be injected safely either into the
retrobulbar or peribulbar space; subsequent diffusion
will ultimately block the relevant nerves.
Selection of Patients and Blocks
Numerous published studies confirm the preference
of ophthalmologists, anaesthetists and patients for
local anaesthetic techniques. However, the preferred
technique varies from topical anaesthesia, through
cannula-based block to needle-based blocks. There
is conflicting evidence about whether there are real
differences in effectiveness of blocks, suggesting that
peribulbar and retrobulbar anaesthesia produce
equally good akinesia and equivalent pain control.
There is insufficient evidence in the literature to
make a definitive statement concerning the relative
effectiveness of sub-Tenon's block in producing akinesia when compared with peribulbar or retrobulbar
block. The technique chosen depends on a balance
between the patient’s wishes, the operative needs of
the surgeon, the skills of the anaesthetist and the type
of surgery.
Preoperative assessment is generally limited to medical history, drug history and physical
examination. According to the UK Joint Colleges
Guidelines 2012, routine investigations are unnecessary if local anaesthesia is to be employed and these
are performed only if it is thought that the results
may lead to improved general health of the patient.
Patients are not fasted and this is particularly helpful in managing patients with diabetes mellitus who
can receive all their normal medications and achieve
better glycaemic control in the perioperative period. The blood sugar concentration should still be
checked. Patients receiving anticoagulants and antiplatelet agents are advised to continue their usual
medications unless told otherwise. Warfarin therapy
is not considered an absolute contraindication to local anaesthesia provided that the preoperative INR
value is in the therapeutic target range; a sub-Tenon’s
block or topical anaesthesia is preferred. The axial
length of the eye is usually measured before cataract surgery and serious caution in the use of needle
blocks is required if the axial length exceeds 26 mm
(Fig. 30.6) or if the axial length is unknown, e.g. in
surgery for glaucoma. Antibiotics are not necessary
in patients with valvular heart disease. Premedication
is not usually necessary but, if needed, may be given
intravenously just before the local anaesthetic block
is inserted.
OPHTHALMIC REGIONAL BLOCKS
A
B
C
22 mm
Axial length
611
close to the optic nerve. Akinesia and analgesia result
quickly but a facial nerve block is essential to block
the orbicularis oculi muscle. Both classical retrobulbar and facial nerve blocks are associated with significant sight- and life-threatening complications and
these techniques have been replaced by the modern
retrobulbar block.
Modern Retrobulbar Block. Surface anaesthesia is
­obtained with local anaesthetic drops (oxybuprocaine
0.4% or similar). The conjunctiva is cleaned with
aqueous 5% povidone iodine. Evidence-based literature suggests that the eye should be kept in the neutral (primary) gaze position at all times and a needle
length shorter than 31 mm is inserted through the skin
or conjunctiva in the inferotemporal quadrant as far
lateral as possible below the lateral rectus. The needle is
directed upwards and inwards, with the needle ­always
tangential to the globe. A volume of 4–5 mL of local
anaesthetic agent of choice such as 2% lidocaine is injected. A separate facial nerve block is not required.
35 mm
Band placed
around globe
FIGURE 30.6  Eyeballs of various shapes. (A) Normal eyeball. (B) High myope. (C) Scleral buckle applied after surgery
for retinal detachment.
OPHTHALMIC REGIONAL BLOCKS
Insertion of an intravenous cannula is good practice
and must be established if a sharp-needle technique is
planned. Full cardiopulmonary resuscitation equipment and trained staff should be immediately available. Appropriate cardiorespiratory monitoring should
be used. Ophthalmic regional anaesthesia should provide conditions appropriate for the surgeon’s needs
and planned surgery.
Needle-Based Blocks
Atkinson described the classical retrobulbar block in
1936. In this technique, the patient is asked to look
upward and inward. A needle 38 mm in length is inserted at the junction of the medial 2⁄3 and lateral 1⁄3 of
the inferior orbital margin after raising a wheal of skin
with local anaesthetic. The needle is directed towards
the apex and 2–3 mL of local anaesthetic is injected
Inferotemporal Peribulbar Block. Surface anaesthesia
and asepsis are obtained as above. The globe is kept in
a neutral gaze position and a needle of less than 31 mm
in length is inserted as far as possible in the extreme
inferonasal quadrant through the conjunctiva or lower
lid. A peribulbar block is essentially similar to a modern retrobulbar block but the needle is not directed
upwards and inwards and the needle always remains
tangential to the globe along the inferior orbital floor
(Fig. 30.7). A volume of 5–6 mL of local anaesthetic
agent is injected. However, more than 60% of patients
require a supplementary injection in the form of a medial peribulbar block.
Medial Peribulbar Block. A supplementary injection is often required either in the same quadrant or
through an injection in the medial compartment and
is called a medial peribulbar block. A needle is inserted
between the caruncle and the medial canthus to a
depth of 1–1.5 cm and 3–5 mL of local anaesthetic is
injected. A single medial peribulbar block with 6–8 mL
of local anaesthetic has been advocated if akinesia is
essential in patients with myopic eyes.
In practice, the differentiation between retrobulbar
and peribulbar block is more semantic than actual. If
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30  OPHTHALMIC ANAESTHESIA
Equator of globe
SR
LR
Optic nerve
IR
FIGURE 30.7  Intraconal injection is placed between the
inferior border of the lateral rectus and the inferior rectus. SR,
superior rectus; LR, lateral rectus; IR, inferior rectus.
the onset of anaesthesia is rapid with a peribulbar anaesthetic, then the chances are that it has found a direct
pathway or been injected directly into the cone.
The gauge of needle should be the finest that can
be used comfortably but this is usually limited to a
­25- or 27-gauge needle. Finer needles are difficult to
­manipulate but larger needles may cause more pain and
damage. Sharp needles are used because blunt ­needles
are painful to insert and cause vasovagal ­
syncope.
The operator should consistently use the same volume ­syringe with the same gauge needle, because it is
then easier to feel and judge the resistance to injection.
A correctly placed injection has minimal resistance.
Gentle digital pressure and massage around the
globe help to disperse the anaesthetic and reduce
IOP. Alternatively, a pressure-reducing device such as
Honan’s balloon can be used. The maximum pressure
should be limited to 25 mmHg in order to avoid compromise to the globe’s blood supply.
Sub-Tenon’s Block. Sub-Tenon’s block involves a minor surgical procedure, and although it avoids some of
the complications of the other two techniques, its use
is associated with some specific problems.
Surface anaesthesia and asepsis are obtained as
above. The lower eyelid is retracted or a speculum
used. The patient is asked to look upwards and outwards. The conjunctiva and Tenon’s capsule are
gripped together with a non-toothed forceps 5–10 mm
from the limbus in the inferonasal quadrant. A small
incision is made through these layers with Westcott
scissors until the white sclera is seen. A sub-Tenon cannula (19-gauge, curved, 2.54-cm long, metal, opening
at the end) is inserted gently along the curvature of the
globe and should pass easily without resistance. In the
posterior capsule, 3–5 mL of local anaesthetic of choice
is injected slowly. The injected local anaesthetic agent
diffuses around and into the intraconal space leading
to anaesthesia and akinesia. Inferotemporal, superotemporal and medial quadrants may also be used to
access the sub-Tenon’s space. A variety of cannulae,
both flexible and shorter lengths, are available. This
method reduces the risk of CNS spread, optic nerve
damage and global puncture but may be more likely
to cause superficial haemorrhage. Akinesia may take
longer to achieve.
Local Anaesthetic Agents and Adjuncts
The ideal local anaesthetic agent should be safe and
painless to inject. It should block motor and sensory
nerves quickly. The duration of action should be long
enough to perform the operation but not so long as to
cause persistent postoperative diplopia.
Lidocaine 2% remains the gold standard. It is safe
and produces effective motor and sensory blocks.
Bupivacaine has largely been superseded by its isomer levobupivacaine, which has less propensity to
cause cardiovascular side-effects. It may be used in
concentrations of 0.5% or 0.75%. Its onset of action
is slower than that of lidocaine but it has a longer duration of action. The more concentrated solution may
cause prolonged diplopia or myopathy if accidentally
injected directly into one of the extraocular muscles.
Prilocaine 2–4% has a rapid onset of action, few sideeffects and a duration of action comparable with that
of bupivacaine. Ropivacaine 1% has also been shown
to be effective.
Hyaluronidase is an enzyme which reversibly li­
quefies the interstitial barrier between cells by depolymerization of hyaluronic acid to a tetrasaccharide,
thus enhancing diffusion of molecules through tissue
planes. The amount of hyaluronidase powder mixed
with the local anaesthetic varies from 5 to 150 IU mL−1.
The use of hyaluronidase for ophthalmic blocks is
controversial and its use for sub-Tenon’s block is
OPHTHALMIC REGIONAL BLOCKS
questioned for a short operation such as cataract surgery. Side-effects are rare but include allergic reactions,
orbital cellulitis and formation of pseudotumours.
A vasoconstrictor such as adrenaline is commonly
added to local anaesthetic solutions to increase the intensity and duration of block and minimize bleeding
from small vessels. Absorption of local anaesthetic is
reduced, which avoids any surge in plasma concentrations. Adrenaline may cause vasoconstriction of the
ophthalmic artery, compromising the retinal circulation, and has also been implicated in complications
in the elderly with cardiovascular and cerebrovascular
comorbidities.
Commercial preparations of lidocaine and bupivacaine are acidic in solution and the basic local anaesthetic exists predominantly in the charged ionic
form. The non-ionized form of the local anaesthetic
agent which traverses the lipid membrane of the
nerve produces the conduction block. At higher pH
values, a greater proportion of local anaesthetic molecules exist in the non-ionized form and this allows
more rapid influx into the neuronal cells. Adjustment
of the pH of levobupivacaine and lidocaine by the
addition of sodium bicarbonate allows more of the
local anaesthetic solution to exist in the uncharged
form. Alkalinization has been shown to decrease the
onset time and prolong the duration of action after
needle blocks but its use in clinical practice is probably unwarranted.
Complications of Ophthalmic
Regional Blocks
Reported complications of needle blocks abound. They
range from mild to serious, and may affect the eye or
be systemic. Orbital complications include failure of
the block, corneal abrasion, chemosis, subconjunctival
haemorrhage, orbital haemorrhage, globe damage, optic nerve damage and extraocular muscle malfunction.
Systemic complications such as local anaesthetic agent
toxicity, brainstem anaesthesia and cardiorespiratory
arrest may occur as a result of intravenous injection or
spread or misplacement of drug in the orbit during or
immediately after injection.
Sub-Tenon’s block is considered a safe alternative to
needle block but a number of minor and major complications have been reported. Minor and frequent
complications such as pain during injection, reflux
613
of local anaesthetic, chemosis and subconjunctival
haemorrhage occur with varying incidences. Visual
analogue pain scores are typically low but even minor
discomfort in the orbit may be interpreted as severe
and ­unpleasant pain. Smaller cannulae may afford a
marginal benefit. Anterograde reflux and loss of local
anaesthetic on injection occurs if the dissection is oversized relative to the gauge of the cannula. Inadequate
access into the sub-Tenon’s space can also promote
chemosis. The i­ncidence of chemosis varies with the
volume of local anaesthetic, dissection technique and
choice of cannula. Shorter cannulae are associated
with an increased likelihood of conjunctival chemosis.
Conjunctival haemorrhage is common. In one study of
patients taking drugs with the potential to impair coagulation, conjunctival haemorrhage occurred in 19% of
the control group, 40% of patients taking clopidogrel,
35% of those ­taking warfarin and 21% of patients taking aspirin. The incidence can be reduced with careful
dissection, application of topical adrenaline or, controversially, the use of handheld cautery.
Orbital Haemorrhage
Orbital haemorrhage is a sight-threatening complication of intraconal and extraconal anaesthesia as well
as, rarely, sub-Tenon’s block (Fig. 30.8). It occurs with
a frequency of between 0.1 and 3% following needlebased blocks. The haemorrhage may be venous or arterial in origin and may be concealed or revealed. Venous
bleeding is slow and usually stops. Venous haemorrhage usually presents as markedly bloodstained chemosis and raised IOP. It may be possible to reduce the
IOP by digital massage and cautious application of an
IOP-reducing device to such an extent that surgery can
proceed safely. Before the decision is made to proceed
with surgery or postpone it for a few days, it is advisable to measure and record IOP. Arterial bleeding is
rapid, with blood filling the periorbital tissues, increasing tissue volume and pressure. This is transmitted to
the globe, raising the IOP. Urgent measures must be
taken to stop the haemorrhage and reduce IOP. Firm
digital pressure usually stops the bleeding and, when
it has been arrested, consideration must be given to reducing the IOP so that the blood supply to the retina is
not compromised. Lateral canthotomy, acetazolamide
or mannitol, or even paracentesis, may need to be considered in consultation with the ophthalmologist.
614
30  OPHTHALMIC ANAESTHESIA
Concealed
haemorrhage
FIGURE 30.8  CT scan taken in coronal section of a patient following an intraconal haemorrhage. Note the marked
proptosis of the right eye and the confined space occupied
by the haemorrhage. This was a concealed haemorrhage because, despite elevated intraocular pressure and proptosis, no
signs of bleeding or bruising were evident until the next day.
Prevention of Haemorrhage. Straining due to anxiety
during the block leads to engorgement and potential
puncture of vessels around the eye. Sedation may help
and the patient should be encouraged to breathe quietly through an open mouth and so prevent a Valsalva
manoeuvre. The fewer injections that are made into
the orbit, the less are the chances of damaging a blood
vessel. Cutting and slicing movements at the needle
tip should be avoided. Fine needles are less traumatic
than thicker ones. Deep intraorbital injections must be
avoided. The inferotemporal quadrant has fewer blood
vessels and is less hazardous. It is advisable to apply
firm digital pressure to the orbit as soon as the needle
is withdrawn after any intraorbital injection, as this
­reduces any tendency to ooze.
Central Spread of Local Anaesthetic Agent
Mechanism. The cerebral dura mater provides a tubular sheath for the optic nerve as it passes through
the optic foramen. This sheath fuses to the epineurium of the optic nerve, providing a potential conduit
for ­local anaesthetic to pass subdurally to the brain.
Central spread can occur on injection if the needle tip
has entered the optic nerve sheath. Central spread following sub-Tenon’s block has also been reported. Even
an injection of a small volume of local anaesthetic
may enter the central nervous system and/or cross
the optic chiasma to the opposite eye and may cause
life-­threatening sequelae, e.g. catastrophic cardiores­
piratory collapse. The time of onset of symptoms is
variable but usually appears in the first 15 min after injection. Central spread may occur on rare occasions if
an orbital artery is cannulated by the needle tip, resulting in retrograde spread up the artery until it meets a
branch, where it can then flow in a cephalad direction;
in addition to orbital haemorrhage, systemic collapse
is almost instantaneous.
Signs and Symptoms of Central Spread. The symptomatology of central spread is varied and depends
upon which part of the central nervous system is affected by the local anaesthetic. Because of the anatomical proximity of the optic nerve to the midbrain, it
is usual for this area to be involved. Signs and symptoms involving the cardiovascular and respiratory
systems, temperature regulation, vomiting, temporary
hemiplegia, aphasia and generalized convulsions have
been described. Palsy of the contralateral oculomotor
and trochlear nerves with amaurosis (loss of vision)
is pathognomonic of central nervous system spread
and should be sought in any patient whose response to
questions following block are not as crisp as they were
beforehand.
Treatment of Central Spread. Cardiorespiratory arrest may occur and should be treated as at any other
arrest. Bradycardia requires treatment with an anticholinergic drug. Asystole has been reported rarely,
but if it occurs, intravenous vasoactive drugs are required. Respiratory depression or apnoea necessitates
ventilatory support, intravenous fluid therapy and
administration of supplemental oxygen. Convulsions
are treated with an intravenous induction agent such
as propofol, or a benzodiazepine.
Prevention of Central Spread. Intraconal or extraconal injections should always be undertaken with the
patient looking in the neutral or the primary gaze position. The optic nerve is a C-shaped structure and there
is slackness in the primary gaze position so that it lies
out of the way of the advancing needle (Fig. 30.9). If
the needle encounters the optic nerve in this position,
OPHTHALMIC REGIONAL BLOCKS
615
Equator of globe
Axis of rotation
Optic nerve
A
FIGURE 30.10  Ultrasound scan of a normal eyeball (left)
and a high myope.
B
C
FIGURE 30.9  Movements of the optic nerve in relation
to eyeball movement when the needle is introduced into the
cone from the inferotemporal quadrant. (A) Primary gaze. (B)
Upwards and inwards. (C) Downwards and outwards.
it is unlikely to damage or perforate its sheath because
slackness in the structure allows the nerve to be pushed
aside. The most dangerous position is when the patient looks upwards and inwards, as this presents the
stretched nerve to a needle directed from the inferotemporal quadrant. The injection should not be made
deep into the orbit, where the optic nerve is likely to
be tethered.
Damage to the Globe
Global puncture is a serious complication of ophthalmic blocks. It has been reported following both
intraconal and extraconal blocks and even following sub-Tenon’s and subconjunctival injection.
Perforation of the globe has entry and exit wounds
whereas penetration of the globe has only the wound
of entry. With appropriate care, it should be a very
rare complication because the sclera is a tough structure and, in most patients, is not perforated easily.
Puncture of the eyeball is most likely to occur in
­patients with high myopia, previous retinal banding,
posterior staphyloma or a deeply sunken eye in a narrow orbit. Not all globes are the same length and not
all orbits are the same shape. In most patients who
present for cataract surgery, axial length of the eyeball
is measured with ultrasound (Fig. 30.10) to calculate
the power of the intraocular lens. Normal globes have
an axial length of 20–24 mm. Patients with high myopia have much longer axial lengths and extreme caution with needle blocks should be exercised in these
patients.
Puncture of the globe is usually recognized at the
time of surgery and presents as an exceptionally soft
eye with a loss of red reflex. In cataract surgery, if the
block is good, the surgeon should be encouraged to
proceed with the lensectomy but to stitch up the eye
with twice as many sutures as normal. Without lensectomy, it may not be possible to observe the damage to
the posterior segment of the eye. It can be expected
that the needle track through the vitreous will form
a band of scar tissue. If this is not excised, it contracts
and detaches the retina, sometimes causing sudden total blindness in the affected eye.
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30  OPHTHALMIC ANAESTHESIA
Optic Nerve Damage
This is a rare but late complication which usually results from obstruction of the central retinal artery or
direct trauma following classical retrobulbar block
with a long needle. This artery is the first and smallest
branch of the ophthalmic artery arising from that vessel as it lies below the optic nerve. It runs for a short
distance within the dural sheath of the optic nerve
and, about 35 mm from the orbital margin, pierces
the nerve and runs forward in the centre of the nerve
to the retina. Damage to the artery may cause bleeding into the confined space of the optic nerve sheath,
compressing and obstructing blood flow. If the complication is recognized soon enough, surgical decompression of the optic nerve is performed.
Extraocular Muscle Malfunction
The inadvertent injection of a long-acting local anaesthetic into any extraocular muscle mass may result
in muscle damage manifesting as prolonged weakness, fibrosis or even necrosis of the muscle. The oldfashioned classical retrobulbar technique in which the
needle was inserted between the lateral ⅓ and medial
⅔ junction of the inferior orbital rim predisposed to
this complication. The safest site for inferotemporal
injection is the extreme temporal area just below the
lateral rectus. Recent evidence suggests that the addition of hyaluronidase to the local anaesthetic agent
helps to disperse the agent before lasting damage can
be done. Persistent diplopia following local anaesthesia
should be investigated with a suitable scan because urgent surgical intervention to the affected muscle may
be required.
OPHTHALMIC DRUGS RELEVANT TO
THE ANAESTHETIST
β-Adrenergic blockade (e.g. timolol) decreases IOP by
reduction of production of aqueous humour. Topical
administration of drugs can cause clinically significant
concentrations in the plasma via nasal drainage and
the systemic side-effects of timolol including hypotension, bradycardia and bronchospasm are well reported.
Phenylephrine applied to the eye intraoperatively to
dilate the pupil can cause myocardial ischaemia and
hypertension. Prostaglandin analogues (e.g. latanoprost) increase the uveoscleral outflow of aqueous,
reducing intraocular pressure. α-Adrenergic drugs
(e.g. clonidine) have the same effect.
Carbonic anhydrase inhibitors (e.g. acetazolamide)
reduce aqueous formation and are used orally or intravenously to treat or prevent increases in IOP. These
are sulphonamides without bacteriostatic actions and
should not be used in patients with a relevant allergy.
They can cause an acidosis (renal loss of bicarbonate)
and a diuresis as a result of their effects on the renal
tubules. The acidosis can be made worse in the perioperative period if the effect of opioids and anaesthesia
reduce respiratory compensation.
Hypertonic mannitol increases aqueous outflow.
Initial increases in blood pressure and systemic blood
volume are followed by a diuresis. The use of intraoperative diuretics necessitates the use of urinary catheterization. Ecothiopate is of historical interest as a
treatment for intraocular hypertension because it irreversibly bound to cholinesterase and could last for
a week; the duration of action of succinylcholine was
therefore prolonged significantly.
ANAESTHESIA FOR SPECIFIC
OPHTHALMIC PROCEDURES
REQUIRING GENERAL ANAESTHESIA
Penetrating Eye Injury
The penetrating open eye injury attracts first place in
the list, if only because of its perceived importance
in examinations undertaken by trainee anaesthetists.
Eye injuries may be difficult to inspect in detail because of swelling and pain and exploration under
general anaesthesia may be required at the earliest
opportunity. The potential for loss of intraocular
contents exists even if penetration is not obviously
present preoperatively. Eye injury may also coexist with other major head injuries or polytrauma.
The incidence of penetrating eye injury is highest
in young adult males although the introduction of
seatbelt legislation brought about a significant reduction. As with any trauma, there may be a short
fasting time before the injury and subsequent delay
in gastric emptying, especially if alcohol was consumed before the injury or if an opioid was administered in the Emergency Department. The situation
may therefore exist of anaesthesia for a patient with
a potentially full stomach.
ANAESTHESIA FOR SPECIFIC OPHTHALMIC PROCEDURES REQUIRING GENERAL ANAESTHESIA
In patients with penetrating eye injury alone or associated with other trauma, general anaesthesia is routine.
Orbital regional anaesthesia has been used successfully
in some centres. The classical dilemma of rapid tracheal
intubation to prevent aspiration using succinylcholine
and the subsequent risk of increased IOP causing loss of
eye contents is a balance of anaesthesia risk versus surgical risk. The overwhelming importance is to choose
the anaesthetic technique which minimizes the risk of
pulmonary aspiration of gastric contents most effectively throughout the perioperative period, but consideration should be given to reducing the IOP until the
eye is made safe. In principle, therefore, the use of succinylcholine as the muscle relaxant with the fastest onset
of good or excellent intubating conditions, in association with cricoid pressure, is first choice. However, large
retrospective studies of penetrating eye injury have not
shown vitreous loss to be clinically significant.
The urgency of surgery has the greatest i­nfluence
on the anaesthesia decision-making process.
Ophthalmologists are currently more likely to choose
to wait for 6 h after the last meal or often, due to the
time of day, wait until morning before exploring the
eye. This is dependent on the severity of the injury as
well as the potential to produce a good ocular outcome.
There is little incentive to risk aspiration and death if
there is little likelihood of preserving vision as the benefit. If appropriate fasting delays have been followed,
the anaesthetist is in a position to make whatever anaesthetic choice is suitable for any other intraocular
surgery with similar airway risk factors.
Surgery may be bilateral and lengthy and subsequent return to theatre for repeated procedures is also
common. Loss of vision in one or both eyes following
accidental injury in the young population understandably heightens preoperative anxiety.
Cataract Surgery
Cataract surgery has been revolutionized in recent
decades and the need for complex anaesthesia has
diminished. Phacoemulsification surgery is increasingly performed with smaller gauge probes and the
procedure can be performed under topical anaesthesia, although many ophthalmologists prefer a block
technique. The use of sub-Tenon’s block is common
and needle-based block is avoided in many countries.
General anaesthesia is almost a rarity.
617
Vitreoretinal (VR) Surgery
VR surgery covers a range of intra- and extraocular
procedures which may involve lengthy periods of
time in the dark. Anaesthetic considerations relating to length of procedure and individual choices of
technique and airway are described above. The use
of a local block is common, with both needle- and
­cannula-based blocks in use. General anaesthesia is
used in younger patients or if surgery is expected to
exceed the patient’s ability to remain comfortable.
Of particular interest is the relevance of the use of
nitrous oxide in general anaesthesia. Vitrectomy removes all the vitreous from the eye with the purpose
of clearing cloudy or bloody vitreous, as well as performing intraocular procedures on the retina. The integrity and pressure of the vitreal cavity is determined
by the surgeon throughout the procedure whilst the
structured jelly-like apparatus is removed. The cavity may then be filled with an air/gas mixture (commonly perfluoropropane or sulphur hexafluoride) or
silicone. The surgeon may make a decision on which
of these to use towards the end of surgery and therefore it is sensible to avoid the use of nitrous oxide
for vitrectomy surgery because, if an air/gas mixture
is used by the surgeon, nitrous oxide in equilibrium
in the eye cavity may diffuse out quickly at the end
of the procedure, leaving a lower pressure in the eye
than surgically intended. This can cause detachment
or re-detachment of the retina. If nitrous oxide has
been used, it should be switched off well before the
insertion of surgical gas into the vitreal cavity. Gases
may persist in the eye for up to three months postoperatively and the non-ophthalmic anaesthetist needs
to be aware of the relevance of ophthalmic gases. A
wrist band is placed on the patient after surgery to
alert any subsequent anaesthetist to avoid nitrous oxide; nitrous oxide would diffuse into the cavity faster
than nitrogen would diffuse out and the IOP could
increase, with serious consequences. Likewise, flying can cause the bubble to expand. The gas diffuses
out of the eye slowly over time. Silicone oil used for
the same purpose needs to be removed surgically at
a later stage. Nitrous oxide use is of no relevance if
silicone oil has been used.
Retinal surgery can also be performed from outside the sclera. Buckling, bands, cryotherapy and laser
therapies are used to repair breaks. The eye requires a
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30  OPHTHALMIC ANAESTHESIA
lot of surgical manipulation during these procedures
and the oculocardiac reflex can be profound and recurrent. Anticholinergic prophylaxis may be helpful.
The VR anaesthetist may find that the operating list is
very flexible because some detachments (e.g. macular
detachment) require urgent surgery and are therefore
common additions to the list at the end of the day.
Subsequent repeated operations are very common.
General anaesthetic considerations remain the same;
however, local anaesthesia may become complicated
by adhesions related to the original surgery.
Strabismus Surgery
This is the most commonly performed paediatric
ophthalmic procedure and is usually undertaken as a
day-case. Airway considerations of head and neck procedures apply but a laryngeal mask airway is the most
commonly selected technique, particularly in older
children. Long-acting opioids are not required and are
likely to increase an already high risk of postoperative nausea and vomiting. Surgery itself requires tension to be applied to the extraocular muscles. Steady
deep anaesthesia with or without muscle relaxation
(to guarantee immobility) allows the surgeon to gauge
how much muscle repositioning is required. However,
it is the tension applied by the surgeon to the muscle
which can cause severe bradycardia, especially in the
vagally responsive child. Prophylaxis with glycopyrronium is recommended. Strabismus surgery in children
has been linked to a first presentation of malignant
hyperthermia and temperature measurement is mandatory. Standard measures to control postoperative
pain and reduction of nausea and vomiting should be
considered.
Glaucoma Surgery
If general anaesthesia is required, most of the considerations are the same as for cataract surgery. However,
unlike most ocular surgery, intraoperative miosis is required although this is not a contraindication to the
use of intravenous atropine. A still, soft eye makes the
surgical procedure easier to perform. Neuromuscular
blockade and good anaesthetic control over IOP variables produce ideal conditions.
Dacrocystorhinostomy
Dacrocystorhinostomy (DCR) is a procedure performed for watery eyes. There is surgical exposure
of the tear duct and a new opening is created into
the nasal cavity. This is a relatively stimulating procedure. General anaesthesia is suitable although local
anaesthesia (with or without sedation) has gained
popularity. The operation may be performed with
an open technique or through a nasal endoscope
although, in relation to anaesthesia, the considerations are similar. All normal ophthalmic anaesthetic considerations apply. However, there is the
additional risk of blood in the airway during and
immediately after the procedure. Tracheal intubation and the safe use of a throat pack offer airway
protection. Measures to prevent blood ooze at the
site of surgery can aid the surgeon and these include
hypotension, head-up position and the use of vasoconstriction in the surgical field. Xylometazoline
or cocaine provides vasoconstriction in the nose.
Endoscopic laser DCR is another surgical operation
and the anaesthetist should have additional training
in the practicalities of laser airway surgery. The laser
safety officer will provide the correct eye protection
for the anaesthetist.
Other Oculoplastic Procedures
The range of surgery for this subspecialty relates to
the lid, socket or adnexae. Many procedures are short
and lid surgery is generally performed under local anaesthesia. Longer procedures such as enucleation and
tumour surgery are generally performed under general anaesthesia and appropriate measures are taken
to provide postoperative pain relief. Bilateral blepharoplasties for cosmetic reasons are increasingly frequent and, in common with all oculoplastic surgery,
the requirements for a bloodless field are best met
with controlled relative hypotension and surgical site
vasoconstriction.
Paediatric Procedures
In addition to strabismus surgery, children, including infants and neonates, may require other
ophthalmic procedures. Although the majority of
children are ASA I or II and may be managed as day
cases, there are a number of patients with associated
comorbidities who require detailed examinations
or ocular surgery. Congenital cataracts, glaucoma,
vascular and lens disorders can occur in diseases
such as Down’s, mucopolysaccharidoses, craniofacial and connective tissue disorders. Retinopathy of
CONCLUSION
prematurity may require treatment in sick neonatal
patients outside the theatre suite. Anaesthetic considerations relevant to the condition balanced with
the surgical requirements guide anaesthesia choices.
An infant with airway anomalies may require a
complex anaesthetic skill-set simply to undergo
ophthalmoscopy.
Sedation and Ophthalmic Blocks
Sedation is used commonly in conjunction with topical anaesthesia. Selected patients in whom explanation and reassurance have proved inadequate may
benefit from sedation. Short-acting benzodiazepines,
opioids and small doses of intravenous anaesthetic
induction agents are favoured but the dosage must be
minimal. The routine use of sedation is discouraged
because of an increased incidence of adverse intraoperative events. It is essential that, when sedation is
administered, a means of providing supplementary
oxygen is available. Equipment and skills to manage any life-threatening events must be immediately
accessible.
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CONCLUSION
The practice of anaesthesia has seen preferences for local or general anaesthesia for ophthalmology repeatedly swing in both directions since Koller introduced a
choice, using cocaine almost 130 years ago. Currently,
the preference is firmly in favour of local anaesthesia
and a practising ophthalmic anaesthetist should possess skills in a range of different techniques to deal with
the needs of different operations, operators and, most
importantly, patients. There is no place for ad hoc attendance in the eye unit or occasional practice.
FURTHER READING
Kumar, C.M., Dodds, C., 2006. Sub-Tenon's anesthesia. Ophthalmol.
Clin. North Am. 19, 209–219.
Kumar, C.M., Dowd, T.C., 2006. Complications of ophthalmic regional blocks: their treatment and prevention. Ophthalmologica
220, 73–82.
Kumar, C.M., Dodds, C., Fanning, G.L. (Eds.), 2002. Ophthalmic
anaesthesia. Swets and Zeitlinger, Netherlands.
Joint guidelines from the the Royal College of Anaesthetists and the
Royal College of Ophthalmologists: 2012. http://www.rcoa.ac.uk/
system/files/LA-Ophthalmic-surgery-2012.pdf. Accessed 24.06.13.
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