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426 Theory and Practice of Squint and Orthoptics
operatively. The scope of orthoptic treatment
includes:
• Elimination of convergence insufficiency
• Fusion training, to increase fusion amplitude
• Antisuppression exercises
• Treatment of anomalous retinal correspondence
• Treatment of amblyopia
• Control of deviation
Order of orthoptic treatment
The natural course of events, when a heterophoria slowly becomes a heterotropia and is left
untreated, in order of occurrence include:
• Deterioration of amplitudes
• Occurrence of diplopia
• Development of suppression and development
of amblyopia (in a monocular deviation).
However, the orthoptic treatment in a patient
with heterotropia proceeds in the opposite
direction as follows:
• Amblyopia is treated first, to be followed by
• Antisuppression therapy,
• Diplopia training, and
• Amplitude improvement.
Delivery of orthoptic treatment
The details of the orthoptic treatment required
for various neuromuscular anomalies of the eye
have been described along with the concerned
anomaly. However, for a quick review, they are
listed below.
1. Treatment of convergence insufficiency.
Orthoptic treatment of convergence insufficiency
is quite effective (for details, see page 167). It
includes the following:
• Pencil convergence exercises
• Physiological diplopia exercises
• Training for increasing fusional convergence
with base-out prisms or on synoptophore.
2. Exercises for increasing fusional amplitudes.
Both convergence and divergence fusional
amplitudes can be increased by fusion training
using:
• Prisms or
• Major amblyoscope
(for details, see pages 225 and 226)
Indications
• To compensate a latent strabismus
• To improve control of an intermittent
strabismus
• As a pre- and postoperative measure in constant
strabismus
3. Orthoptic treatment of suppression includes
the following:
• Diplopia exercises
• Vergence control in heterophoria and surgical
alignment of eyes in large tropias.
• Differential stimulation
• Macular massage
• Occlusion therapy
(for details, see page 186)
SURGICAL MANAGEMENT
Extraocular muscle surgery is only a part of the
therapeutic management of a strabismic patient.
Of course, the squint surgery is aimed to
produce and maintain a condition in which the
visual axes of the two eyes are directed without
conscious effort to the object of fixation whatever
its position. However, in some cases, this may
require more than one operation and in others
it may even not be possible at all. All these facts
should be made amply clear to the patient and/
or the parents.
INDICATIONS FOR SQUINT SURGERY
1. To correct squint cosmetically as well as
functionally. This is possible in cases in which
the visual acuity of the two eyes is equal or has
been made nearly equal by appropriate
occlusion treatment (so that alternation occurs
easily) and in which binocular function has been
improved (where possible) by appropriate
orthoptic treatment, if indicated.
2. To correct the squint only cosmetically. This
is indicated in old children and adults who have
untreatable deep amblyopia, persistent
abnormal retinal correspondence and absence
of power of fusion. Patients having sensory
squint secondary to organic disorders (e.g. optic
atrophy, central chorioretinitis) are also
corrected cosmetically only.
Principles of Non-Surgical and Surgical Management of Strabismus
427
3. To relieve marked asthenopic symptoms
squint surgery may be indicated, in some cases.
These include patients with phorias and
intermittent tropias which could not be treated
by an active orthoptic treatment.
4. To correct abnormal head posture which may
be assumed by some patients to relieve diplopia
(e.g. in superior oblique or lateral rectus
weakness) or to improve vision (e.g. with
nystagmus and an eccentric null point).
5. To relieve mechanical restriction or to
improve appearance surgery may be required
sometimes in patients with hypertrophied
conjunctiva or Tenon's capsule from prior
muscle surgery.
OPTIMAL TIME FOR SQUINT SURGERY
Optimal time for squint surgery varies
depending upon the type of squint, age of the
patient and presence of various sensory
adaptations as below.
1. CONCOMITANT SQUINT
Although it is difficult to be dogmatic as to
precisely when to operate upon a case of
concomitant squint, especially in a child, the
following suggestions have been made by
experienced strabismologists:
i. Children too young for orthoptic treatment,
i.e. those below 4–5 years should be considered
for operation as follows:
• If a constant squint is present after wearing of
glasses (where indicated) for a month and the
squint is an alternating one or that an early
alternation has been established by appropriate
occlusion, i.e. vision is almost equal in the two
eyes; the child should be operated as early as
possible. Such a recommendation has been
made on the basis of the observation that in
young children, if the visual axes are put
within a few degrees of parallelism by means
of operative treatment, and good binocular
vision may develop per se, provided that the
child already possesses some rudimentary
development of his normal binocular reflexes.
• In intermittent squint with or without glasses,
the surgery should be delayed and child
should be observed and refracted every six
months. Orthoptic treatment should be started
as early as possible. In many cases with
intermittent squint the need for operation may
be dispensed altogether with glasses and/or
orthoptic treatment. However, before
abandoning the idea of surgery, it must be
ascertained that squint has completely
disappeared and not that there has occurred
mere reduction in the angle of deviation
(which may be satisfactory from the cosmetic
point of view but of no functional value).
ii. In children old enough for orthoptic treatment
(i.e. those above 4–5 years), following
considerations should be made:
• Before the surgery is performed for a constant
squint, best possible efforts with optical and
orthoptic treatment should be made to treat
the associated (if any) sensory adaptation
(such as suppression, amblyopia and abnormal retinal correspondence). The efforts
should be aimed at developing good binocular
vision with fusion amplitudes.
• In the presence of an abnormal retinal corres-
pondence, now most surgeons recommend
early surgery; since both cosmetic and
functional results may be obtained in many
cases (i.e. ARC disappears spontaneously after
surgery).
• In the absence of a true fusion, the case may
have to be assessed purely for the cosmetic
effect. However, it has been reported that
parallelism of the visual axes produced by an
early surgery, may sometimes result in
development of binocular fusion.
iii. In older children (above 12 years of age) and
adult patients who have deep intractable
amblyopia (functional or organic) the time of
surgery may be decided according to personal
requirements for cosmetic purposes only, since
there is hardly any scope for a functional cure.
2. PARALYTIC SQUINT
The most important principle is to establish over
a significant period of time that the condition is
stable and that no spontaneous improvement is
likely to occur. Therefore, a hastily surgical
treatment may result in an over-correction of the
deviation in some cases. On the other hand in
some cases the condition may continue to
428 Theory and Practice of Squint and Orthoptics
deteriorate so that ill-time surgical interference
will prove to be inadequate. However, in most
cases if the condition remains static for a period
of 3–6 months, the surgical treatment may be
considered.
Expectations from the treating ophthalmologists regarding optimal time to operate
It is expected that the operating ophthalmologist should be ready with the following
spade work and home task when he decides that
it is the optimal time to operate:
• He should have accomplished all the
preoperative measures which are necessary
and helpful to achieve the basic three goals
of squint management.
• He should have a plan as to what surgery will
be performed and why.
• By this time, he must educate the parents and/
or patients as to the goals, his plan of attack,
the risks involved in surgery, the risks
involved in not operating, and the possibility
that more than one operation may be
necessary.
• He should have plans for what to do post-
operatively:
– If the patient is fusing,
– If the patient is overcorrected, and
– If the patient is undercorrected.
TYPES OF SURGICAL TECHNIQUES FOR
SQUINT CORRECTION
A. MUSCLE WEAKENING PROCEDURES
1. Recession of an extraocular muscle is the most
commonly performed weakening procedure.
This procedure weakens the muscle action by
changing its arc of contact with the globe.
2. Marginal myotomy is infrequently indicated.
This procedure weakens the muscle by reducing
the number of contractile fibres and not by
changing the arc of contact. Therefore, it is
effective in further weakening on already
maximally recessed muscle. This procedure is
also indicated where recession cannot be
performed as in patients with very thin sclera
and in those having buckle implants.
3. Myectomy also weakens the muscle by
reducing the contractile fibres and is seldom
performed nowadays except by some surgeons
especially for inferior oblique muscle.
4. Free tenotomy or disinsertion of the rectus
muscles may be performed in desperate cases.
Oblique muscle tenotomy is practised by many
surgeons to weaken this muscle.
5. Posterior fixation suture also known as
Faden operation or retropexy of an extraocular
muscle is a weakening procedure that does not
affect the deviation in primary position but
weakens the muscle action in patients who are
already orthotropic. However, it reduces the
deviation in esotropic patients, when performed
on medial rectus. Faden operation is performed
under following circumstances:
– To correct the dissociated vertical deviation.
– Patients having incomitant strabismus with
orthotropia in primary position.
– To treat upshoot and downshoot of the
adducted eye in patients with Duane's
retraction syndrome type I.
– Esotropia with a variable angle.
– Persistent esotropia after maximal recession
and resection surgery.
– To dampen the nystagmus.
It has been reported by von Noorden that the
Faden operation is most effective, when
performed on the medial rectus, less effective
on vertical rectus muscles and least effective on
the lateral rectus muscle.
6. Recession of conjunctiva and Tenon's capsule
may also help in augmenting the weakening
effect of a rectus muscle especially in patients
with large deviations of long standing where the
elasticity of conjunctiva and Tenon's capsule is
impaired and where scars have been formed
from previous surgery.
7. Muscle lengthening by insertion of a silicone
expander or non-absorbable suture material has
been recommended as a more controlled
weakening procedure for superior oblique
muscle.
B. MUSCLE STRENGTHENING PROCEDURES
1. Resection is the most commonly performed
muscle strengthening procedure. This procedure
Principles of Non-Surgical and Surgical Management of Strabismus
429
strengthens the muscle by shortening its length.
One should avoid excessive resection of a
muscle, since this may restrict the eye
movements in the opposite direction.
2. Advancement of the muscle insertion towards
limbus is usually not preferred as the primary
procedure alone. However, it may be combined
with the resection procedure or may be used as
secondary procedure in already resected muscle
to further strengthen it or in cases with
overcorrection due to recession of a muscle.
3. Tucking of an extraocular muscle also
enhances its action. This procedure is not being
preferred for rectus muscles. However, a
superior oblique tucking is performed
frequently to strengthen this muscle. This
procedure, when performed on the superior
oblique muscle, is quite effective in improving
the depression of the adducted eye and in
counteracting the excyclotropia.
Provides a wider field of view and better
access to the extraocular muscles and so is
Suitable for more complex surgeries requiring
extensive muscle work.
C. PROCEDURES THAT CHANGE DIRECTION OF
MUSCLE ACTION
1. Vertical transpositioning of the horizontal
recti is recommended in patients with A- or V-
pattern without associated oblique muscle
dysfunction.
2. Horizontal transpositioning of the vertical
recti has also been recommended by some
surgeons for correction of A-V pattern.
3. Slanting of the rectus muscle insertion has
also been recommended by some surgeons for
correction of A-V-patterns. However, at present,
it is not a preferred technique.
4. Transplantation of muscles in paralytic
squint (see page 460).
D. PERIOSTEAL FIXATION OF THE GLOBE MEDIAL
1. Medial periosteal fixation of globe is
recommendation in patients with third nerve
palsy
2. Lateral periosteal fixation of lateral rectus
after disinsertion is also recommended in
patients with third nerve palsy.
CHOICE OF OPERATION AND
AMOUNT OF SURGERY
Choice of operation and amount of extraocular
muscle surgery to be performed depend upon
multiple factors, i.e. type and angle of squint,
age at the time of onset of squint, duration of
squint, age at the time of operation, visual status,
convergence and accommodation status.
Therefore, degree of squint correction versus
amount of extraocular muscle manipulation
required cannot be mathematically determined.
A discussion on this aspect of squint management can be considered under following heads:
• General considerations for planning squint
surgery
• Guidelines for planning squint surgery
• Rough estimates for amount of squint surgery
GENERAL CONSIDERATIONS FOR
PLANNING SQUINT SURGERY
As we know, it is not possible to provide a
readymade menu for correcting each patient
with strabismus, rather the plan of surgery has
to be tailor made for the individual patient. The
clinical factors other than the measurement of
deviation in primary position which need to be
considered in the planning are as follows:
1. Amblyopia. As discussed under the 'optimal
time for surgery', the surgery should be delayed
till the vision has been made equal or nearly so
by appropriate means such as glasses and
amblyopia therapy, when needed. However, if
the visual acuity cannot be made equal, the
surgery should preferably be performed on the
eye with poor vision.
2. Vertical incomitancy. Presence of A- or V-
pattern should be taken into consideration while
planning surgery for the horizontal strabismus.
The surgical treatment may include an
additional surgery on the oblique muscle or
vertical transpositioning of the horizontal recti.
3. Horizontal incomitancy. In the presence of a
mechanical restriction or paretic limitation of the
eye movements, the deviation in left gaze and
right gaze may differ significantly from the
deviation in primary gaze. Surgeon should aim
at making the alignment more nearly comitant
after surgery.
For example, in a patient with 30° exotropia
in primary position, 20° in right gaze and 40° in
430 Theory and Practice of Squint and Orthoptics
left gaze, the surgery may be modified as
below:
• If bilateral lateral rectus recession is planned,
a more recession on left than the right side
may be performed to have greater reduction
of the exotropia in left gaze.
• If a resect-recess procedure is planned to get
a greater reduction in exotropia in left gaze, a
greater recession of the left lateral rectus and
less resection of the left medial rectus than the
standard amounts of surgery should be
performed.
In other words, testing of versions is very
important in deciding the appropriate surgical
technique as follows:
• In esotropia associated with excessive adduction
and normal abduction, a maximal recession of
the medial rectus and a nominal resection of
the lateral rectus should be performed.
• In esotropia associated with normal adduction and
a deficient abduction, a maximal resection of the
lateral rectus and a nominal recession of the
medial rectus should be performed.
• In exotropia associated with excessive abduction
and normal adduction a maximal recession of
the lateral rectus and a nominal resection of
the medial rectus should be performed.
• In exotropia associated with normal abduction and
deficient adduction, a maximal resection of the
medial rectus and a nominal recession of the
lateral rectus should be preferred.
• When the strabismus is associated with a normal
abduction and adduction, one should prefer the
strengthening (resection) rather than the
weakening (recession) procedure.
• When the strabismus is associated with an
excessive movement in one direction and deficient
on the other, one should prefer to do maximal
weakening of the muscle in the excessive
movement and maximal strengthening of the
muscle with deficient movement.
All the above recommendations have been
made by the workers with an aim to normalize
the excursions of the eyes along with correction
of deviation.
4. Lateral incomitancy. One must consider the
measurements in lateral gaze while planning
surgery in a patient with intermittent exotropia. It
has been observed that standard amounts of
surgery may result in overcorrection in patients
having lateral incomitancy (e.g. in a patient with
exotropia of 30° in primary position and of 20° in
right as well as left gaze). It has been recommended
that amount of recession of each lateral rectus
should be reduced by 1 mm in such patients.
5. Previous surgery. The details of the previous
surgery performed (wherever possible), its
results and effects (any mechanical restriction,
etc.) should be duly taken into consideration
while planning a repeat surgery as follows:
• Though planning for an under- or over-
corrected squint should be made as for a fresh
case of squint, it is preferable to operate on
muscles that have not had prior surgery.
• In the presence of a mechanical restriction
from excessive resection/scarring or weakness
from excessive recession, reoperation on the
involved muscle may provide better results.
• In multiple surgeries, one must ensure that at
least one rectus muscle remains unoperated
in each eye.
6. Distance and near measurements and AC/A
ratio should also be taken into consideration
while planning surgery for horizontal deviations.
Duane classified horizontal deviations on the
basis of distance/near measurements as follows:
Esodeviations
• Basic esotropia—distance deviation equals near
deviation. Some surgeons prefer a monocular
recession of the MR and resection of LR in
such cases. While others prefer bilateral
symmetrical recession of medial recti.
• Convergence excess type esotropia—near
deviation greater than distance. Bilateral
medial rectus recession is preferred by some
surgeons over monocular recess-resect
procedure.
• Divergence insufficiency type esotropia—
distance deviation greater than near. Bilateral
lateral rectus resection is preferred by some
surgeons over uniocular recess-resect
procedure.
Exodeviations
• Basic exotropia—distance and near deviation is
equal. Some surgeons prefer a monocular
recession of the LR and resection of MR in such
cases. While others prefer bilateral symmetrical
recession of lateral recti.
Principles of Non-Surgical and Surgical Management of Strabismus
431
• Convergence insufficiency type exotropia—near
deviation is greater than distance. This
condition rarely requires surgery. Some success
has been reported with bilateral MR resections.
• Divergence excess type exotropia—distance
deviation greater than near deviation, normal
AC/A ratio, no increase in near deviation on
occlusion. Bilateral lateral rectus recession is
preferred by many surgeons over uniocular
recess-resect procedure.
• Pseudo or simulated divergence excess type of
exotropia. In this condition, distance deviation
measures greater than near deviation on
routine examination. But after occlusion test,
near deviation increases to equal the distance
deviation. Uniocular recess-resect procedure
is preferred by most surgeons.
7. Special considerations for cyclovertical
strabismus. While considering surgery for the
vertical strabismus, one must make the note of
deviation in right gaze and left gaze and also in
upgaze and downgaze of the same eye. And in
general, surgery should be performed on those
muscles whose field of action is in the same field
as the greatest vertical deviation.
8. Forced duction test (FDT) should always be
performed before planning the surgery. In small
children, FDT should be performed under
general anaesthesia just before surgery, and if a
mechanical restriction is detected, the original
surgical plan may have to be changed
accordingly. However, it should be kept in mind
that when succinylcholine has been used, a
sustained contraction of the extraocular muscles
may occur for a period of about 20 minutes.
Therefore, it is better to use a non-depolarizing
muscle relaxant in squint surgery, since it will
not alter the FDT.
GUIDELINES FOR PLANNING SQUINT SURGERY
General guidelines based on the experience of
various squint surgeons which can help in
planning the squint surgery are as follows:
1. Surgeon factor. Every surgeon gets a different
amount of correction vis-a-vis another surgeon
for the same amount of surgery. Therefore, it is
advisable that each surgeon must standardise
one's approximate effectiveness of a particular
procedure based on review of his/her experience.
2. Degree of squint. The same amount of muscle
surgery will give greater correction for larger
deviations vis-a-vis smaller deviations.
3. Age of the patient and duration of squint. A
more extensive surgery may be required in older
children and adults having squint of long
duration as compared to small children for the
same amount of deviation, since in the former,
secondary anatomical changes take place in the
muscles and fascia.
4. Recession versus resection. In general,
weakening of a muscle by recession produces
more correction per millimetre of surgery visa-vis strengthening of a muscle by resection.
Therefore, relatively larger amounts of resection
are required to produce an effect comparable to
that achieved by recession of the antagonist.
5. Intractable amblyopia. In the presence of an
intractable amblyopia, it is not possible to predict
the results of surgery. This point should be made
amply clear to the patient and/or parents.
6. Medial versus lateral rectus surgery. In
general, a recession of the medial rectus muscle
is more effective than the same amount of
recession performed on a lateral rectus muscle.
7. Horizontal versus vertical rectus muscles.
Recession of the vertical rectus muscles is much
more effective than the recession performed on
the horizontal rectus muscles.
8. Combined recession-resection operation
provides more correction than the added results
of each procedure, when performed alone.
Further, this procedure is more effective in
stabilizing the surgical results vis-a-vis single
procedure, since the resection procedure
reduces the amount of contracture that normally
occurs in recessed antagonist.
ROUGH ESTIMATES OF AMOUNT OF SQUINT SURGERY
As mentioned earlier, it is not possible to
provide a surgical dose-response curve or tables
for correcting strabismus. Nevertheless, the
conclusions drawn by experienced surgeons
may serve as rough estimates for the beginners.
However, once again it is stressed that surgeons
should standardize their own approach by
retrospectively and continuously reviewing
their own results and adjusting the amount of
surgery for attaining the best possible results.
For standardizing their surgery, it is mandatory
432 Theory and Practice of Squint and Orthoptics
Table 15.1 Rough estimate of amount of extraocular muscle surgery for esotropia
Deviation in Monocular surgery in mm Binocular surgery in mm
prism dioptres
15 3.0 4 3.0 4.0
20 3.5 5 3.5 5.0
25 4.0 5 4.0 5.5
30 4.5 6 4.5 6.0
35 5.0 7 5.0 6.5
40 5.5 7 5.5 7.0
50 6.0 8 6.0 8.0
60 6.5 9 6.5 9.0
70 7.0 10 7.0 10.0
Table 15.2 Rough estimate of amount of extraocular muscle surgery for exotropia
Deviation in Monocular surgery in mm Binocular surgery in mm
prism dioptres
15 4.0 3.0 4.0 3.0
20 5.0 4.0 5.0 3.5
25 6.0 4.5 5.5 4.5
30 7.0 5.0 6.0 5.5
35 7.5 5.0 6.5 6.0
40 8.0 6.0 7.0 6.5
50 9.0 7.0 8.0 7.5
60 10.0 8.0 9.5 8.0
70 10.0 10.0 8 mm bilateral LR recession +
80 8 mm bilateral LR recession +
Recession of +Resection of Bilateral or Bilateral or
MR LR MR recession LR resection
Recession of +Resection of Bilateral or Bilateral
MR LR MR recession LR resection
8 mm MR resection of one eye
8 mm bilateral MR resection
that surgeons should use the ocular motility
measurements and judgement made by
themselves. The rough estimates of surgicaldosage have been described along with the
different types of strabismus. However, for a
ready reference, they are again summarized in
Tables 15.1 and 15.2.
ANAESTHESIA FOR SQUINT SURGERY
Three types of anaesthesia commonly used in
strabismus surgery are:
• Topical anaesthesia
• Local anaesthesia
• General anaesthesia
TOPICAL ANAESTHESIA
Use and indications. It has been recommended
that use of topical anaesthesia produces
adequate analgesia without affecting the motor
supply of extraocular muscles and thus allowing
the readjustment of muscle position during
surgery to affect cosmetic or functional results.
It is especially useful where unpredicted results
are anticipated.
Technique. Topical anaesthesia can be achieved
by instillation of either 4% cocaine, 0.5%
proparacaine or 0.5% tetracaine drops, four
times every 4 minutes, before the conjunctival
incision is made. It is important to note that after
Principles of Non-Surgical and Surgical Management of Strabismus
433
the conjunctiva is opened, further anaesthetic
drops should not be instilled, since paralysis of
extraocular muscles will occur and thus the
main advantage of topical anaesthesia will be
lost.
Prerequisites. Topical anaesthesia can be used
in co-operative adults only. In addition, a very
fine handling is required during surgery under
topical anaesthesia. Excessive pulling and
manipulation produces pain; so topical
anaesthesia is effective for simple recession
procedures, and not for resection procedures or
for recession procedures involving restricted
muscles where exposure is difficult. Further, it
is recommended that no barbiturates or high
doses of analgesics be given preoperatively, since
these will affect the angle of deviation during
surgery and thus the mere purpose of topical
anaesthesia will be defeated. It should be ensured
that a suitable target and cover device should be
available in the operation theatre to check the
alignment during the procedure.
Disadvantages. Topical anaesthesia is not
effective in controlling the pain produced by
pulling on or against a muscle and thus not
suitable in all cases. Further, it can be used only
in very co-operative adults and is thus not much
popular.
LOCAL ANAESTHESIA
Local anaesthesia is commonly used for squint
surgery in older co-operative children and
adults. It allows a very comfortable and smooth
surgery by producing lid and ocular anaesthesia
and akinesia.
Techniques. Local anaesthesia can be achieved
either by—(1) a combination of surface
anaesthesia, facial nerve block and retrobulbar
block or (2) a combination of surface anaesthesia
and peribulbar block.
Surface and topical anaesthesia is achieved as
described above.
Facial block. For intraocular surgery, it is
necessary to block the facial nerve which
supplies the orbicularis oculi muscle, so that
patient cannot squeeze the eyelids.
Orbicularis akinesia can be achieved by
blocking the facial nerve at its terminal branches
(Van Lint block), superior branches (Atkinson
block) or proximal trunk (O'Brien or Nadbath
block).
1. Blocking the peripheral branches of facial nerve
(Van Lint's block): This technique blocks the
terminal branches of the facial nerve, producing
localised akinesia of the orbicularis oculi muscle
without associated facial paralysis.
In this technique, 2.5 ml of anaesthetic
solution is injected in deeper tissues just above
the eyebrow and just below the inferior orbital
margin, through a point about 2 cm behind the
lateral orbital margin, level with outer canthus
(Fig. 15.1).
Fig. 15.1 Technique of van Lint's facial block.
2. Facial nerve trunk block at the neck of mandible
(O'Brien's block). In it, facial nerve is blocked
near the condyloid process. The condyle is
located 1 cm anterior to the tragus. It is easily
palpated, if the patient is asked to open and close
the mouth with the operator's index finger
located across the neck of the mandible. At this
point, the needle is inserted until contact is made
with the periosteum and then 4–6 ml of local
anaesthetic is injected while the needle is
withdrawn (Fig. 15.2).
This technique is associated with pain at the
injection site and unwanted facial paralysis.
3. Nadbath block: In this technique, the facial
nerve is blocked as it leaves the skull through
the stylomastoid foramen. This block is also
painful.
4. Atkinson's block: In it, superior branches of the
facial nerve are blocked by injecting anaesthetic
solution at the inferior margin of the zygomatic
bone.
434 Theory and Practice of Squint and Orthoptics
Fig. 15.2 Distribution of facial nerve and technique of
O'Brien's block.
Retrobulbar block. It was introduced by
Herman Knapp in 1884. It is administered by
injecting 2 ml of anaesthetic solution (2%
xylocaine with added hyaluronidase 5 IU/ml
and with or without adrenaline one in one lac)
into the muscle cone behind the eyeball. It is
usual to give the injection through the inferior
fornix or the skin of outer part of lower lid, with
the eye in primary gaze (Fig. 15.3B). The needle
is first directed straight backwards then slightly
upwards and inwards towards the apex of the
orbit, up to a depth of 2.5 to 3 cm (Fig. 15.4B).
Retrobular block anaesthetises the ciliary
nerves, ciliary ganglion and third and sixth
cranial nerves thus producing globe akinesia,
A
B
Fig. 15.3 Position of needle on the lower eyelid skin for
peribulbar block (A) and retrobulbar block (B).
Fig. 15.4 Position of needle for peribulbar block in the
peripheral orbital space (A) and for retrobulbar block in the
muscle cone (B).
anaesthesia and analgesia. The superior oblique
muscle is not usually paralysed as the fourth
cranial nerve is outside the muscle cone.
Complications encountered with it include
retrobulbar haemorrhage, globe perforation,
optic nerve injury, and extraocular muscle
palsies.
Peribulbar block. This technique described in
1986 by Davis and Mandel has almost replaced
the time tested combination of retrobulbar and
facial blocks, because of its fewer complications
and by obviating the need for a separate facial
block.
Primarily, the technique involves the injection
of 6–7 ml of local anaesthetic solution in the
peripheral space of the orbit (Fig. 15.4A), from
where it diffuses into the muscle cone and lids,
leading to globe and orbicularis akinesia and
anaesthesia. Classically, the peribulbar block is
administered by two injections; first through the
upper lid (at the junction of medial one-third
and lateral two-thirds) and second through the
lower lid (at the junction of lateral one-third and
medial two-thirds) (Fig. 15.3A). After injection
orbital compression for 10–15 minutes is applied
with digital massage, superpinky or any other
method.
The anaesthetic solution used for peribulbar
anaesthesia consists of a mixture of 2%
lignocaine, and 0.5–0.75% bupivacaine (in a ratio
of 2:1) with hyaluronidase 5 IU/ml and
adrenaline one in one lac.
Principles of Non-Surgical and Surgical Management of Strabismus
435
GENERAL ANAESTHESIA
Indications. General anaesthesia is indicated for
squint surgery in infants, small children and also
in anxious, uncooperative and mentally
retarded adults and those patients willing for
surgery only under general anaesthesia.
Special consideration during general anaesthesia for squint surgery
• It is recommended that if the child with
esotropia is on miotic therapy (phospholine
iodide or other cholinestrase agents), it should
be discontinued at least 6 weeks prior to
surgery so that the blood cholinestrase levels
can be returned to normal before surgery. If
this has not been possible, the anaesthesiologist should be warned that the use of
succinylcholine is contraindicated.
• Since succinylcholine causes sustained
contraction of extraocular muscles for about
20 minutes, so it will alter the forced duction
test (FDT). Therefore, it is better to use a nondepolarising muscle relaxant in squint
surgery, since it will not alter the FDT.
Advantages of general anaesthesia. The main
advantage of general anaesthesia is that it
produces complete analgesia and akinesia and
does not require patient's cooperation during
the surgical procedure. Needless to say that
while performing surgery under general
anaesthesia, the ophthalmologist is most
comfortable and is relieved of serious
responsibilities.
Disadvantage of general anaesthesia in squint
surgery. (1) In general there is increased risk, i.e.
not present in topical and local anaesthesia.
(2) General anaesthesia is more costly and
requires services of an experienced anaesthesiologist. (3) Incidence of oculocardiac reflex
(bradycardia), oculodepressor reflex (hypotension) and oculorespiratory reflex (apnoea) is
higher under general anaesthesia. Therefore, it
is recommended that a retrobulbar anaesthesia
should be given (to block the afferent pathway
of these reflexes), even when the squint surgery
is being done under general anaesthesia.
(4) Under general anaesthesia, it is not possible
to relate eye position with the preoperative
deviation and postoperative results. This
preposition is to be particularly kept in mind in
esotropia, since the eye under general anaesthesia
may look less esotropic or even exotropic. This
situation may intimidate an inexperienced
surgeon, who may perform less surgery,
resulting in under-correction; and thus another
surgery may be required.
COMMON OPERATIVE STEPS IN
SQUINT SURGERY
Fixation of the globe
For fixation and rotation of the globe in different
directions, 6-0 or 5-0 Mersilene or silk suture on
spatulated needle is passed through the
conjunctiva and episcleral tissue near the limbus
at following positions:
• For horizontal rectus muscle surgery—at 12
and 6 o' clock positions (Fig. 15.5A).
• For vertical rectus muscle surgery—at 9 and
3 o'clock positions.
• For inferior oblique muscle surgery—at about
4½ o'clock in left eye and at about 7½ o'clock
in right eye (i.e. near the limbus in inferotemporal quadrant).
After applying the traction sutures the eyeball
is rotated away from the muscle on which
surgery is being performed, e.g. laterally for
surgery on the medial rectus (Fig. 15.5A).
Conjunctival incision and exposure of the muscle
The conjunctival approaches recommended for
exposure of the rectus muscles are: (1) Limbal
incision approach, (2) transconjunctival or Swan
approach, and (3) cul-de-sac or fornix approach.
The technique, advantages and disadvantages of each approach are described here in
brief.
Limbal incision or von Noorden's approach
Technique
1. At the limbus, conjunctiva and Tenon's
capsule are fused together. This conjoined tissue
is grasped close to the limbus with forceps and
a small radial incision perpendicular to the
limbus is made with the help of scissors
(Fig. 15.5B).
2. The dissection is then carried concentric with
the limbus by spreading the blades of a blunttipped Westcott spring-action scissors beneath
the conjoined layer; which is then severed.