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416 Theory and Practice of Squint and Orthoptics
III. Surgical techniques in patients having headtilt associated with childhood nystagmus
Some patients with childhood nystagmus (CN)
have a combination of both horizontal and
rotatory components with latter being the major
component. Patients which have a significant
headtilt have a torsional null position, and
shifting the null position by torsional
Kestenbaum is suggested in such cases.
The basic principle to correct head tilt (not
related to paralysis of any cyclovertical muscle)
is to rotate the eyes in the direction of the
headtilt, which can be accomplished by any of
the following surgical techniques of torsional
Kestenbaum:
1. Surgery on two oblique muscles
In this technique, for example, in a patient with
head tilt towards right shoulder, the eyes can
be surgically rotated to the right by:
• Weakening of right superior oblique muscle (either
by a tenotomy or a recession of the anterior
fibres), and
• Weakening of the left inferior oblique with a
recession or some other weakening procedure.
2. Surgery on four oblique muscles
On the basis of Kestenbaum’s principle, some
workers have proposed symmetrical surgery on
all the four oblique muscles (torsional
Kestenbaum). For instance, in a patient with head
tilt towards the right shoulder, the following
surgery has been recommended:
Right eye is excycloducted by recessing the anterior
and retropositioning the posterior aspect of the
superior oblique tendon and advancing the
anterior and anteropositioning the posterior
aspect of the inferior oblique tendon.
Left eye is incycloducted by advancing the anterior
portion and anteropositioning the posterior edge
of the superior oblique tendon and by recessing
the anterior portion and retro-placing the
posterior position of the inferior oblique insertion.
• Right medial rectus—transposed downwards.
• Right lateral rectus—transposed upwards.
4. Surgical slanting of the insertion of all four
rectus muscles
Spielmann has recommended this surgery, for
example, in a patient with head tilt towards right
the right eye is excycloducted by recession of the:
• Temporal part of the superior rectus
• Nasal part of the inferior rectus
• Inferior part of the lateral rectus, and
• Superior part of the medial rectus.
Note. A special care is required to preserve the
blood supply of the anterior segment of the
eyeball in this operation.
5. Horizontal transpositioning of the vertical
rectus muscles
von Noorden et al have recommended this surgery (as a preference over the other surgeries),
for example, in a patient with head tilt towards
right as follows:
Right eye should be excyclotorted by transposing the
right superior rectus nasally and the right inferior
rectus temporally.
Left eye should be incyclotorted by transposing the
left superior rectus temporally and left inferior
rectus nasally.
They have recommended that transposition of
each muscle should be by one full muscle width
without changing their distance from the limbus.
(B) SURGICAL TECHNIQUES FOR NYSTAGMUS
BLOCKAGE (DAMPENING) SYNDROME
1. Recession of the MR and resection of LR of
the converging eye has been recommended by
Adelstein and Cuppers with good results.
2. Bilateral medial rectus recession sometimes
combined with posterior fixation sutures has
been reported to be a more effective and thus a
better choice than the recess-resect procedure.
3. Vertical transposition of the horizontal rectus
muscles
Decker has reported vertical transposition of the
horizontal rectus muscles, e.g. to cause
excycloduction of the right eye as follows:
(C) SURGICAL TECHNIQUES FOR DECREASING
THE NYSTAGMUS INTENSITY
1. Producing an artificial divergence (prismatically and surgically) have been reported to be
of some use.
Nystagmus and Related Oscillations
417
Surgical procedure consists of bilateral medial
rectus recession.
Aim of the surgery is to induce a latent divergent
ocular position which the patient will then
overcome by exerting fusional convergence,
thereby damping the nystagmus.
For the success of procedure, the patients must
have adequate fusional reserves to overcome the
induced deviation, so, preoperative testing with
prisms is mandatory.
Indications include patient with INS and
convergence dampening with near vision >
distance vision.
Benifits of the surgery include:
• Dampening of nystagmus occurs by 70–80%.
• Improvement in vision in magnificant.
2. Maximal recession of all the four horizontal
rectus muscles has been recommended for
decreasing the nystagmus intensity. For
undisturbing the balance of forces, it has been
recommended that a 10 mm of bilateral MR
recession and 12 mm of bilateral LR recession is
the best procedure. However, before contemplating such a surgery, it should be made amply clear
to the patient that this operation will only decrease
its intensity and not eliminate the nystagmus.
Note. Large 4-muscle recessions or muscle
extirpations are not preferred presently.
3.Tenotomy and reattachment. All the four
horizontal recti are detached and resutured at
the same insertion.
Indications. Nystagmus with no null, primary
position null or alternating null (periodic or
aperiodic).
Benefits of surgery include 25% reduced
intensity of nystagmus, broadening of null zone,
improvement in vision by 1 to 3 logMar units in
about 50% of patients and 40% increase in NAFX
in 90% of patients.
4. Augmented Anderson procedure. It comprises:
• MR recession: 9 mm, and
• LR recession: 12 to 13 mm.
Indications. Patients with INS and face turn <25°.
Benefits of surgery include:
• Dampening of nystagmus by 90%.
• Improvement in vision in magnification.
Y-splitting of the lateral rectus muscle: In cases
where nystagmus is associated with vertical
drifts, Y-splitting of the lateral rectus muscle can
be performed. The muscle is divided into two
parts, and one part is repositioned to reduce the
unwanted vertical movements.
Neurosurgical procedures: In rare cases where
nystagmus is associated with underlying
neurological conditions, neurosurgical
interventions may be considered. These
procedures target brain structures or pathways
involved in eye movement control.
NYSTAGMUS-LIKE OCULAR MOTOR
OSCILLATIONS
Nystagmus-like oscillations can be described as
below:
• Inappropriate saccades
• Voluntary saccadic oscillation ‘nystagmus’
• Roving eye movements
INAPPROPRIATE SACCADES
Involuntary inappropriate saccades include:
Saccadic intrusions
These are basically transient breaks in fixation.
These may occurs as:
• Square wave jerks. These are small amplitude
conjugate saccades (<5°) which moves the eye
away from fixation and back again (Fig. 14.17A).
• Square wave pulses also known as macro-
square wave jerk have a large amplitude (>5°)
and a shorter intersaccadic latency (100–
150 ms) (Fig. 14.17B). They are usually and
indication of neurological malfunction.
Saccadic oscillations
These movements oscillate across fixation and
usually have amplitude large than 5°. Saccadic
oscillations are of following types:
• Macro-saccadic oscillations. They have a
similar intersaccadic latency to square wave
jerk (Fig. 14.17C). They can reliably
distinguished from ocular flutter only by eye
movement recording.
• Ocular flutter occurs due to interruption of
cerebellar connection to brainstem. It is
characterized by horizontal oscillation and
418 Theory and Practice of Squint and Orthoptics
Fig. 14.17 Inappropriate saccades: (A) Square wave jerk;
(B) Macro-square wave jerks; (C) Macro-saccadic
oscillations; and (D) Ocular flutter.
inability to fixate after change of gaze. Ocular
flutter represent back to back horizontal
scaddes without any interscaddic latency
(Fig. 14.17D)
• Opsoclonus refers to combined horizontal,
vertical and/or torsional oscillations associated with myoclonic movement of face, arms
and legs. It is seen in patient with encephalitis.
Opsoclonus has a similar waveform to ocular
flutter but is multidirection and associated
with oscillopsia.
• Superior oblique myokymia is characterized
by monocular, rapid, intermittent, torsional
vertical movements (which are best seen on
slit-lamp examination).
• Ocular bobbing refers to rapid downward
deviation of the eyes with slow updrift. It
occurs due to pontine dysfunctions.
VOLUNTARY SACCADIC
OSCILLATIONS ‘NYSTAGMUS’
Voluntary saccadic oscillations ‘nystagmus’
refers to the voluntary, poorly sustained
conjugate oscillation of the eyes consisting
of rapidly alternating small-amplitude saccades.
Characteristic features. The oscillations are
conjugate, usually horizontal and symmetrical,
and consist of back-to-back saccades. The
oscillations can be sustained only for a matter
of seconds; convergence is usually associated
with either the initiation or the maintenance of
the oscillation. The amplitude of the movement
is small and the frequency high. There may be a
familial basis for the ability to initiate voluntary
‘nystagmus’ or it may be learned. Voluntary
‘nystagmus’ can be readily differentiated from
acquired nystagmus and does not require
further investigation.
ROVING EYE MOVEMENTS
Roving eye movements refers to conjugate large
amplitude low-frequency horizontal pendularlike movements. The movements are apparent
soon after birth and are generally associated
with severe anterior visual pathway disease
such as Leber’s congenital amaurosis and severe
forms of bilateral optic nerve hypoplasia. With
time the amplitude becomes smaller and a
congenital nystagmus waveform may become
superimposed on the roving pattern or may
replace it.
BIBLIOGRAPHY
1. Boyle NJ, Dawson EL, Lee JP. Benefits of
Retroequatorial Four Horizontal Muscle
Recession Surgery in Congenital Idiopathic
Nystagmus in Adults, JAAPOS, 2006;10:404–8.
2. Dell’Osso LF. Tenotomy and congenital
nystagmus: a failure to answer the wrong
question, Vision Res, 2004;44:3091–4.
3. Erbagci I, Gungor K, Bekir NA. Effectiveness of
retroequatorial recession surgery in congenital
nystagmus, Strabismus, 2004;12:35–40.
4. Flynn JT, Dell’Osso LF. The effects of congenital
nystagmus surgery, Ophthalmology, 1979;86:
1414–27.
5. Hertle RW, Dell’Osso LF. Benefits of retroequatorial four horizontal muscle recession
surgery in congenital idiopathic nystagmus in
adults, JPAAOS, 2007;11:313.
6. Schiavi C, Scorolli L, Campos EC. Surgical
management of anomalous head posture due to
supranuclear gaze palsies and acquired
nystagmus. In: Spiritus M (ed.), Transactions of
the 23rd Meeting of the European Strabismological
Association, Nancy, 1996;229–32.
Nystagmus and Related Oscillations
419
7. Sternberg-Raab A. Anderson–Kestenbaum
operation for asymmetrical gaze nystagmus, Br
J Ophthalmol, 1963;47: 339–45.
8. Wang Z, Dell’Osso LF, Jacobs JB, et al. Effects
of tenotomy on patients with infantile
nystagmus syndrome, JAAPOS, 2006;10: 552–
60.
9. Wang ZI, Dell’Osso LF, Tomsak RL, Jacobs JB.
Combining recessions (nystagmus and
strabismus) with tenotomy improved visual
function and decreased oscillopsia and diplopia
in acquired downbeat nystagmus and in
horizontal infantile nystagmus syndrome,
JAAPOS, 2007;11:135–41.
420 Theory and Practice of Squint and Orthoptics
15
Principles of Non-Surgical and
Surgical Management of Strabismus
NON-SURGICAL MANAGEMENT
Optical treatment
Correction of refractive error
•
Prismotherapy
•
Pharmacologic treatment
Miotics
•
Atropine
•
Botulinum toxin
•
Other drugs
•
Orthoptics
Goals of orthoptics
•
Pre-requisites
•
Indications
•
Order of orthoptic treatment
•
Delivery of orthoptic treatment
•
SURGICAL MANAGEMENT
Indications
•
Optimal time for surgery
•
Types of surgical techniques
•
NON-SURGICAL MANAGEMENT
Goals of Treatment of Strabismus
Goals of treatment of strabismus are:
1. To restore good visual acuity in each eye.
2. To achieve satisfactory cosmetic appearance.
3. To restore, if possible, normal single
binocular vision.
To achieve these goals, treatment of squint
varies for its different clinico-etiological varieties
and has been described along with the each
clinical entity. However, the principles, indications and the techniques of different treatment
modalities available for the squint have been
described here in general. The commonly
practised treatment modalities include:
Choice of operation and amount of
•
surgery
Anaesthesia for squint surgery
•
Common operative steps in squint surgery
•
Recession of rectus muscles
•
Resection of rectus muscles
•
Adjustable sutures in rectus muscle surgery
•
Faden operation
•
Inferior oblique weakening procedures
•
Inferior oblique strengthening procedures
•
Superior oblique weakening procedures
•
Superior oblique strengthening procedures
•
Muscle transposition procedures
•
Complications of extraocular muscle surgery
•
OUTLINES OF STRABISMUS MANAGEMENT
Heterophoria
•
Esotropia
•
Exotropia
•
Vertical and cyclodeviations
•
Incomitant strabismus
•
• Optical treatment,
• Pharmacologic treatment,
• Orthoptics, and
• Surgical treatment.
Non-surgical treatment is essential in all most
all strabismus cases and in many cases may be
sufficient to successfully treat the strabismus
without surgery.
A. OPTICAL TREATMENT
I. CORRECTION OF REFRACTIVE ERROR
Spectacles for correction of refractive error
should be prescribed in every case. These will
improve the visual acuity and provide sharp
retinal image that in young children is essential
as a stimulus for the use of eyes and to achieve
fusion. Refractive correction also provides a
Principles of Non-Surgical and Surgical Management of Strabismus
421
proper balance between accommodation and
convergence and thus at times may correct the
squint partially or completely (as in accommodative esotropia). Some important points
regarding refractive correction in patients with
strabismus are as follows:
General principles for prescribing glasses.
1. In general, full cycloplegic correction should be
prescribed (without making any tonus
allowance for the cycloplegic used),
especially in young children from infancy to
preschool age, neglecting the effect of glasses
on the patient's vision.
2. In school going children, the refractive
correction prescribed should be such that
would provide an optimal distant vision.
3. An overcorrection of +1.0DS to +3.0DS of
the non-amblyopic eye has been advocated
by some workers as penalization treatment.
Role of glasses in esotropia
1. Refractive accommodative esotropia. Full
cycloplegic correction should be made to correct
the esotropia.
2. Non-refractive accommodative esotropia with
high AC/A ratio need to be treated with bifocal
glasses giving full hyperopic correction in the
distance segment and an add of +1.00 D to
+3.5 D in the near segment. The minimum add
required is tested in steps of 0.5D till the
convergence excess for near is controlled.
3. Esotropic patients having associated myopic
should be prescribed minimum myopic lenses
that give best corrected visual acuity.
4. Esotropic patients having associated myopia and
high AC/A ratio also require bifocals.
5. Residual esotropia of small amount (<15 PD)
should be prescribed the maximum hypermetropic correction. If this is insufficient,
additional plus lenses may be tried to ascertain,
if binocular single vision can be achieved.
6. Consecutive esotropia of small amount (<15PD),
persisting after 3 weeks of surgery for intermittent exotropia can be treated by prescribing
full hyperopic correction. Bifocals can be
prescribed, when esotropia is for near only.
Role of glasses in exotropia
1. Undercorrection of hypermetropic error is
recommended to reduce the degree of conse-
cutive exotropia. However, this should not be
at the cost of asthenopic symptoms.
2. Use of over-minus glasses has been suggested
by Jampolsky for controlling the intermittent
exotropia by stimulating accommodation and
convergence in under 5 ear children.
3. Inverse bifocal with a minus add for near has been
suggested for convergence insufficiency type of
exotropia.
II. PRISMOTHERAPY
Prismotherapy for strabismus has become
popular after the introduction of Fresnel presson prisms.
Advantages of Fresnel press-on membrane prisms
include: Light weight, cosmetically acceptable,
easy to apply on the back of patient's glasses,
availability in powers from 0.5D to 30D.
Indications
The indications for prismotherapy in strabismus
are as follows:
I. Role of prisms to assess the effect of surgery
(Diagnostic Prism)
1. Prism adaptation test (PAT). This test has
been advocated by some workers to be
performed before the surgical treatment is
performed in patients with esotropia; while
others do not agree on its utility. In PAT, baseout prisms are given to the patient, so that
esotropia is slightly overcorrected, i.e. to the
point of slight exotropia. The results of the PAT
are interpreted as below:
Favourable response or good fusional prognostic sign
is labelled, when a patient accepts the prism and
demonstrates fusion, when allowed to wear
prisms for several days before surgery. Such
patients are likely to respond well to slight
surgical overcorrection of esotropia and develop
spontaneous restoration of normal retinal
correspondence.
Unfavourable response or poor fusional prognostic
sign is considered, if a patient overconverges in
response to slight overcorrection with the prisms
in PAT and, thus returns with a marked
esotropia in spite of its neutralization with
prism. This overconvergence can occur within
minutes or hours or days or weeks after the
422 Theory and Practice of Squint and Orthoptics
prisms are worn. A further increase in
convergence is reported after addition of prisms
and, the patient is said to eat up the prism.
The overconvergence in response to PAT has
been assumed to occur, most likely, in the
presence of sensory abnormal retinal
correspondence (ARC) and thus represents a
peripheral motor fusional convergence. Such
patients are likely to respond in a way similar
to conventional surgical treatment as well and
thus will have a recurrence of esotropia.
However, in clinical practice, it has been
observed that in many cases, ARC disappears
following surgical alignment without overcorrection. Because of this controversy, PAT has
not become much popular and so most of the
strabismologists no more practice prismotherapy
for sensorial anomalies.
2. To know the response of associated vertical
deviation to surgical treatment for the horizontal deviation. It has been reported that in
some patients, associated vertical deviation also
disappears following prismotherapy for the
associated horizontal strabismus. It is assumed
that in such cases surgical treatment for the
horizontal strabismus alone will be sufficient to
correct the associated vertical deviation as well.
However, like PAT results of this test are also
based on the assumption that the response to
surgical intervention will be similar to the
response to prismotherapy. While in clinical
practice, it may not be cent percent true.
3. To plan the amount of vertical muscle surgery
required in congenital or long-standing vertical
muscle palsies.
II. Role of prisms in managing dilopia and
abnormal head posture (relieving prisms)
Prism may be employed in the early management
till scenario for surgical treatment is clear.
1. Paralytic strabismus. During recovery phase
of paralytic squint, prisms are quite useful in
preventing contracture of the antagonist muscle,
e.g. as in:
• Superior oblique palsy, and
• Sixth nerve palsy.
2. As a temporary measure in acquired ocular
restrictive defects such as blow-out fractures
and thyroid ophthalmopathy, prisms may be
employed in the early management till scenario
for surgical treatment is clear.
III. Maintenance of binocular single vision by
neutralizing the deviation
1. Vertical deviations. Prismotherapy is quite
useful in patients with small (less than 12D)
comitant vertical deviations. However, larger
degrees of vertical deviations associated with
greater degrees of incomitance almost always
require surgery.
2. Horizontal deviations in which therapeutic
use of prisms for relief of diplopia may be quite
successful are:
• Late onset deviations in visually mature patients
such as those associated with muscle paresis
and divergence insufficiency.
• Primary intermittent exotropia. Some workers
have recommended prismotherapy for the
treatment of primary intermittent exotropia,
where surgical treatment is not yet warranted.
However, other workers have reported that
part time occlusion therapy is perhaps more
effective and useful in such cases rather than
the prismotherapy.
3. Surgically overcorrected exotropia. It is
generally agreed that a slight overcorrection
(consecutive esotropia) for 1 to 3 weeks
postoperatively is desirable in patients with
intermittent exotropia. Fusional divergence
usually develops spontaneously to allow the
eyes to straighten. If a stable esotropia persists
over one month postoperatively, it needs to be
corrected by base-out prisms. For a larger
overcorrection requiring resurgery, the base-out
prisms may be prescribed to prevent diplopia
until surgical treatment can be undertaken.
4. Surgically undercorrected exotropia. It has
been reported that in undercorrected exotropia,
the use of overcorrecting base-in prisms (10D
greater than the deviation) in immediate
postoperative period may be successful in
establishing a good fusional result. Hardesty has
described the convergence response to such
prism therapy. However, it has also been
reported that prisms used in this manner,
probably will not be effective, if given later than
three months postoperatively.
Principles of Non-Surgical and Surgical Management of Strabismus
423
5. Surgically undercorrected esotropia. In many
cases of esotropia with ARC in its peripheral
convergence response, a small residual esotropia
with monofixation will be present postoperatively. Prismotherapy in such a deviation is
not indicated, since it will not convert such cases
to bifoveal fixation.
6. Surgically overcorrected convergence
insufficiency may spontaneously lead to
postoperative diplopia. During this period,
prismotherapy may be useful in alleviating
the diplopia.
IV. Management of convergence insufficiency
Convergence insufficiency of hypoaccommodative type and convergence paralysis are also
relieved symptomatically by base-in prisms.
V. Management of heterophorias
Patients with marked asthenopic symptoms,
particularly those with vertical phorias respond
well to prismotherapy.
VI. Role of prisms in nystagmus (see page 412)
Guidelines for prescribing prisms
In principle, the patient should be given the
lowest powered prism which makes him/her
comfortable. The guideline generally applied is
to correct two-thirds of the deviation, but the
variation found in different conditions and
among patients with the same condition make
this rule of little value. Useful guidelines are:
• Patients with acquired vertical muscle palsies
usually require a prism equal or nearly equal
to the angle of deviation.
• Patient with congenital or long-standing palsies
and most patients with dysthyroid eye
disease involving vertical eye movement,
may require as little as half the amount
measured. Patients with long-standing
vertical strabismus caused by retinal
detachment surgery also behave in a similar
way.
• Prism correction. Patients with esodeviations,
especially those which increase in the distance
(divergence weakness type), are harder to
control and, therefore, require a larger prism
in relation to the angle of deviation than do
those with exodeviations.
• Patients with paralytic strabismus who have been
deprived of binocular single vision for many
months may not be able to fuse the images
immediately prisms are introduced. Although
it may not be possible to demonstrate! fusion
in the clinic, it is worthwhile fitting trial prisms
for a period to see whether binocular single
vision can be obtained with more time.
• Patients with very incomitant deviations are
thought to be unsuitable for prism therapy
because the area of binocular single vision
achieved will be too small; however, even a
very small field of binocular fixation is
welcomed by some patients, while others find
the intermittent diplopia too distracting. It is
often worth a short period of trial prisms in
these cases.
Methods of using prisms
Prisms can be used by following methods:
• As Fresnel prism
• In spectacle frames
• As clip-on prism
• Fresnel prisms are the method of choice for
temporary use. Up to 30" can be applied to
either eye but high-powered prisms may not
be tolerated because of their adverse effect on
visual acuity; usually up to 20" can be worn
comfortably, at least by children.
• In spectacle frames. If the patient has a high
refractive error, the spectacle lenses can be
decentred to give the desired effect, provided
that the prism strength is not too great.
Patients with lower refractive errors and those
who are emmetropic can be prescribed
additional prisms. These methods are used,
when permanent or long-term use of prisms
is envisaged.
• Clip-on prisms: These are generally used, only
when the patient cannot tolerate Fresnel
prisms. The strength is limited to 10–12 in
front of each eye because of the weight
involved. These are no longer commercially
available.
B. PHARMACOLOGIC TREATMENT
1. Miotics (see page 244)
Mechanism of action. Though pharmacologic
actions of the miotics (parasympathomimetics)
424 Theory and Practice of Squint and Orthoptics
include miosis and spasm of accommodation,
their utility in strabismus is through their effect
on accommodation.
Miotics commonly used in strabismus management include long-acting cholinesterase
inhibitors such as DFP (0.025% ointment and
0.1% solution), echothiopate (0.03%, 0.06%,
0.125% and 0.25% solution), and demecarium
bromide (0.125% and 0.25% solution).
Indications for use of miotics include:
i. Diagnostic trial to differentiate between
accommodative (refractive and non-refractive)
and non-accommodative esotropia.
ii. Therapy of accommodative esotropia especially
non-refractive type (see page 243).
iii. Postoperative miotic therapy may be useful in
patients with residual esotropia as well as in
consecutive esotropia (after surgery for an
intermittent exotropia).
iv. Amblyopia. Use of miotics in the amblyopic
eye and atropine in the sound eye has been
advocated as penalization treatment for
amblyopia (see page 205).
2. Atropine
Common uses of atropine in the management
of strabismus are as follows:
i. Cycloplegic refraction. Atropine is most useful
for cycloplegic refraction especially in children
with strabismus.
ii. Therapy of accommodative esotropia. A few
workers have recommended atropine in
combination with overcorrection of
hypermetropic refractive error for treatment of
accommodative esotropia.
iii. Amblyopia. Use of atropine in sound eye with
or without a miotic in the amblyopic eye has
been recommended as penalization treatment
for amblyopia.
3. Botulinum toxin
Mechanism of action. Botulinum toxin, when
injected into an extraocular muscle blocks
release of acetylcholine and thus causes
chemical denervation and thus paralysis of the
muscle for several weeks. As a result, the
antagonist muscle becomes comparatively
strong and thus neutralizes the deviation.
Indications. Botulinum toxin may be useful in
the short-term treatment of: Infantile esotropia,
paralytic strabismus especially acute 6th nerve
palsy, surgical overcorrections, Graves'
ophthalmopathy and nystagmus.
Dosage. Botulinum toxin is injected into the
muscle to be weakened under electromyographic (EMG) control after local or general
anaesthesia. When general anaesthesia is used,
ketamine hydrochloride rather than barbiturates
or halothane is used to preserve the EMG signal.
Vertical and horizontal deviations less than 20D
are treated initially with 1.25 to 2.5 units and
horizontal deviations greater than 20D with 2.5
to 5 units initially in volumes of 0.05–0.15 ml.
The saline reconstituted lyophylized powder
must not be shaken otherwise the protein will
denaturate. Reinjections may be titrated down
depending on the effect achieved from the
original injection.
Complications reported following injection
of botulinum toxin are as follows:
i. Diplopia due to transient overcorrection is very
common, but resolves in a few weeks.
ii. Blepharoptosis has been reported to occur in
25% children and 16% of adults after horizontal
muscle injection, due to spillage in the orbit,
which resolved within a few months.
iii. Vertical deviations after horizontal muscle
injection have been reported to occur in 17%
cases, which persisted only in 20% cases.
iv. Perforation of the globe and retrobulbar or
subconjunctival haemorrhage are the other very
rare complications noted.
4. Other drugs
i. Chlordiazepoxide hydrochloride has been
reported to decrease the deviation and/or
improve the fusional amplitude in patients with
esodeviations.
ii. Phenytoin (dilantin) has been reported to
reduce the near point of accommodation and
AC/A ratio and thus affect accommodative and
partially accommodative esotropia.
iii. Levadopa/carbidopa combination has been
used as an adjunct to occlusion therapy in
amblyopia, with no clear role. Some workers
have reported its role in early initiation of the
Principles of Non-Surgical and Surgical Management of Strabismus
425
effect of occlusion in cases of moderate to severe
amblyopia.
iv. Citicoline (CDP choline) has also been
reported to have a role in amblyopic patients. It
is an essential intermediate for phosphatidyl
choline synthesis. It increases cerebral blood
flow and also shows neural restorative effect via
its action on dopaminergic pathway for central
nervous system.
C. ORTHOPTICS
Literally, the word orthoptics means 'straight
eyes'. However, with regard to therapy
orthoptics refers to teaching an individual to
obtain the best possible use of both eyes together
in the form of a comfortable binocular single
vision. Practically orthoptics training is used to
treat convergence insufficiency, to combat
suppression, amblyopia and abnormal retinal
correspondence and to improve fusional
amplitudes and stereopsis.
Goals of orthoptic treatment
The ultimate goals of orthoptic treatment are:
1. Visual acuity levels in each eye should be best
possible.
2. Eyes should be straight—with or without
surgical help.
3. Binocular single vision.
4. Fusion with good amplitudes and reserves.
5. Reduction of refractive glasses (when
involved).
Pre-requisites for a successful orthoptic treatment
1. At the patient level. Since orthoptics is mainly a
training process chiefly concerned with helping
to establish a new sensory pathway that will effect
the accurate usage of the two eyes since this takes
place at the cortical level, therefore, vital prerequisites at the patient level are:
• Reasonable intelligence,
• Physical and psychological maturity,
• Good attention span and,
• Confidence and co-operation.
• Able to attend regularly.
Keeping in view the above points, the age of
patient is very important. It is impossible to treat
orthoptically 2–3 years old. They are too young
to understand and their attention span may only
be 1 or 2 minutes. There are some exceptional
4 years old who understand instructions well
but whose attention span may be too short to
make treatment worthwhile. The age of 5 years
is usually the youngest treatable age. The
average age to begin treatment is 6 years.
2. At the parents' level. Since parents play the
key role in their child's treatment, they must:
• Realize that the reeducation process takes a
long time,
• Have good understanding of the purpose of
the treatment, methods and procedures used,
• Have good rapport between child and
orthoptist.
3. At the orthoptist level. Since orthoptist is the
main person concerned with the treatment, he/
she should:
• Have a friendly but firm attitude towards the
child,
• Have a good rapport and understanding with
the treating ophthalmologist, and
• Win the confidence of child and parents.
4. At the ophthalmologist level. Since it is the
ophthalmologist who refers the child for the
orthoptic treatment, therefore, he should:
• Ensure that the other modes of treatment
required, i.e. refraction and prescription of
glasses, prisms, miotics, etc. have been taken
care of
• Ensure that symptoms must be attributable to
the deviation and not to other causes.
• Must exclued pathological causes for strabismus
• Have frequent conferences with the orthoptist
about the patient's treatment, and
• Take decision about the surgical treatment
whenever required.
Indications of orthoptics
1. Diagnostic indications. A complete orthoptic
work-up is required in each and every patient
suspected of having a neuromuscular anomaly
of the eye.
2. Therapeutic indications. Orthoptic exercises
and training may be required in patients with
phorias and tropias, both pre- and post-