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256 Theory and Practice of Squint and Orthoptics
the points which need special attention are
mentioned here.
1. History should provide information about:
Age of onset, change since onset, frequency of
manifest phase and general health.
2. Visual acuity is usually good. If unequal,
suspect: Anisometropia, microtropia or fundus
pathology.
3. Cycloplegic refraction and fundus examination should be carried out in each case.
4. Cover test should be performed to assess at
1/3 m, 6 m and far distance.
5. Measurement of deviation with prism bar
cover test (PBCT) should be performed in all the
cardinal positions of gaze at near and distance
fixation to discover any associated A- or Vpattern and presence of lateral gaze incomitance
(LGI, i.e. 20% reduction in the angle of squint in
lateral gaze). Detection of LGI is important to
prevent surgical overcorrection.
Measurement of squint should also be made
at a far distance beyond 6 metres since many a
time a larger angle of deviation may be detected.
6. Measurement of stereopsis should be made
during the phoric phase. Both near and distance
stereoacuity should be tested. A progressive
decline in stereopsis is a clear indication to
correct exotropia. Distance stereopsis
deteriorates earlier than the near stereopsis.
7. Occlusion test. It is very important for the
differentiation between true and simulated
divergence excess type of exotropia. Thus in
every child with intermittent exotropia at
distance only or with at least 15 greater
exotropia at distance than near the occlusion test
must be performed. Preferably one eye should
be patched for 24 hours. However, recently it
Fig. 10.9 Patch test for simulated divergence excess type exotropia (for explanation, see text).
Concomitant Esotropias and Exotropias
257
has been reported that only brief period of
occlusion (30 minutes to one hour) is sufficient.
The detailed procedure of the occlusion test is
as follows:
• First of all perform alternate cover test at
distance and near to measure the angle of
exotropia (Fig. 10.9A to C). Let us presume
this step has revealed that exotropia is
significantly greater (15 or more) at distance
than at near.
• Patch is placed over one eye for one hour to
dissociate the eyes thoroughly (Fig. 10.9D).
• After one hour, the fellow eye is covered with
an occluder and the patch is removed
(Fig. 10.9E and F). It is very important to
prevent the patient from using both eyes
simultaneously even momentarily, since only
a brief binocular exposure may be sufficient
to decrease the near deviation by fusional
convergence.
• Again alternate cover test is performed at near
and deviation measured (Fig. 10.9G and H).
In patients with simulated divergence excess
type exotropia, the angle of deviation for near
will increase markedly and will become equal
to the angle for distance (basic type); whereas
with true divergence excess, the near deviation
will remain unchanged, i.e. deviation for
distance will be 15 PD more than the near.
8. +3.0 D spherical lens test. In this test,
measurement for near is performed with and
without +3.0 DS lens in front of the exotropic
eye using an accommodative target which must
be seen clearly. This test is not an alternative to
occlusion test in planning the surgical therapy
(since, the occlusion test removes binocular
fusional stimuli, whereas +3.0 DS lenses provide
only an indication of AC/A ratio). The +3.0 DS
lens test is useful in predicting how a patient
may respond to plus lenses, if surgical overcorrection results.
9. Measurement of fusional amplitudes
• Convergence amplitudes are usually normal
at near and poor to good at distance.
• Divergence amplitudes may be excellent to
poor.
Assessment of control of intermittent exotropia
Assessment of control of intermittent exotropia
before any intervention is useful in predicting
surgical outcome. Following methods of
assessment are in vague:
• Subjective methods
• Objective methods
• Newcastle control score for intermittent
exotropia
• Mayo scale for control in intermittent
exotropia
I. Subjective methods
Office control is graded as below:
• Good control: Patient “breaks” only after cover
testing and resumes fusion rapidly without
need for a blink or refixation.
• Fair control: Patient blinks or refixates to
control the deviation after disruption with
cover testing.
• Poor control: Patient who breaks spontaneously
without any form of fusion disruption.
Home control: At home, parents are told to keep
a chart noting the control of deviation in terms
of the percentage of waking hours the manifest
deviation is noticed at home.
II. Objective methods
Distance stereoacuity testing is useful in noting
the deterioration of fusion, that occurs early in
this disorder. Normal distance stereoacuity
indicates good control with little or no
suppression. The Mentor BVat II BVS assesses
distance stereoacuity using both contour circles
and the ‘Random dot E test’ from 240 to
15 seconds of arc disparity
.
Near stereoacuity: It does not correlate well with
the degree of control in intermittent exotropia
and that performance in this test is only
minimally affected by surgery.
III. Newcastle scoring system
Since the clinic control does not take into account
the duration of tropic phase and the fact that
there is no standardization as to when to
intervene, a novel method was put forth by H.
Haggerty and Richardson, the Newcastle
Control Score. The revised New Castle Score
system seems to be useful in grading the
severity of intermittent exotropia and as a
criteria for surgical intervention.
258 Theory and Practice of Squint and Orthoptics
The Newcastle Control Score (Table 10.4) takes
into consideration the subjective and objective
criteria to grade severity and quantify progress.
The score is the sum total of scores obtained in
home control and in the clinic for near and far.
Total score can vary from 0–7 and patients with
a score of 3 or more are considered to need
surgical intervention. It is a consistent method
of rating severity and enables one to easily
monitor progress.
IV. Mayo scale for scoring of control in
intermittent exotropia
Mayo scoring system (Table 10.5) is based solely
on times observations. An average of three score
is taken to be more reliable. Score (0 to 5) is
measured both at distance and near fixation. So
a total score of 0–10 can be obtained.
Treatment
1. Optical treatment
• Myopia, when present, should be fully
corrected.
Table 10.4 The Newcastle Control Score
Score Component
Home control
0 Squint/monocular eye closure never
noticed
1 Squint/monocular closure seen occasionally
(<50% of time) for distance
2 Squint/monocular eye closure seen
frequently (>50% of time) for distance
3 Squint/monocular closure seen for distance
and near fixation
Clinic control near
0 Manifest only after CT and resumes fusion
without need for blink or refixation
1 Blink or refixate to control after CT
2 Manifest spontaneously or with any form
of fusion disruption without recovery
Clinic control distance
0 Manifest only after CT and resumes fusion
without need for blink or refixation
1 Blink or refixate to control after CT
2 Manifest spontaneously or with any form
of fusion disruption without recovery
The score varies from 0–7: score of 3 or more
significant
Table 10.5 Mayo score for scoring control of
intermittent exotropia
Observation Score
Near Distance
• No exotropia, unless 0 0
dissociated and recovers in
<1 second (exophoria)
• No exotropia, unless 1 1
dissociated and recovers in
1–5 seconds (exophoria)
• No exotropia, unless 2 2
dissociated and recovers in
>5 seconds (exophoria)
• Exotropia <50% of the 3 3
examination before
dissociation
• Exotropia > 50% of 4 4
the examination before
dissociation
• Constant exotropia 5 5
• Hypermetropia up to +2.0 DS need not be
corrected.
• Over minus lenses of 2 to 3D prescribed in
emmetropes or over prescribed in myopes, is
reported to correct x(T) in some children.
2. Prismotherapy
Some strabismologists recommend use of basein prisms to enforce bifoveolar stimulation. They
correct one-half to one-third of deviation by
prisms in order to stimulate fusional covergence.
While other strabismologists like von Noorden
do not prefer to use prisms. However, prismotherapy may be useful in children where surgery
is to be postponed for some period.
3. Orthoptic treatment
Most of the strabismologists agree that, there is
not much role of preoperative orthoptics
treatment in patients with exotropia. However,
following measures may sometimes be useful.
Aim is to make the patient aware of manifest
deviation and to improve the patient's control
over it.
i. Antisuppression exercises. An attempt
should be made to eliminate suppression so that
the patient experiences diplopia whenever the
deviation becomes manifest. Suppression
Concomitant Esotropias and Exotropias
259
scotoma usually and initially is amenable to
therapy by flashes and then the BSV should be
maintained by antisuppression exercises such
as bar reading, cheiroscope or on synoptophore.
The methods of antisuppression treatment are
described in Chapter 8 page 186.
ii. Exercises to improve the patient's control of
the deviation by strengthening the fusional
vergences. Improvement of fusional positive
relative convergence is of particular value in
patients with intermittent exotropia at near only.
The methods described in the treatment of
exophoria (see page 227) may be used with the
aim of ultimately obtaining a normal near point
of convergence. Occasionally, a patient is unable
to control the near exotropia with orthoptic
treatment, in which case, surgery should be
indicated. In such cases, postoperative treatment
to improve the fusional vergences should be
given.
Some people have questioned the effectivity
of convergence exercises in controlling exodeviations. They cannot and do not affect the basic
deviation but by improving the fusion control
decrease the manifestation of an exodeviation,
a tropia being converted into a phoria. The lack
of effect is only due to poor case selection (cases
having suppression may require anti-suppression exercises first) or improper method of
exercising. Appreciation of physiological
diplopia should be taught as the first step.
Secondly, training should be done to increase
both the phasic and tonic control, to improve
the convergence sustenance. Just like any other
physical exercises, the results last till the
exercises are continued. Synoptophore exercises may be desirable to start with but are
insufficient, if not supplemented by proper
home exercises.
For home exercises, special cards or a line on
a plain paper may be made use of or a properly
done "pencil-pushups" may be done.
It should be noted that no convergence
exercises should be done by patients with
intermittent exotropia at distance only, in whom
surgery is planned, for this may lead to
postoperative overconvergence.
iii. Occlusion therapy. It has been reported that
occlusion of preferred eye for 3 to 5 hours a day
for a long period is useful in decreasing the angle
of deviation. In one study, it has been reported
that about 40% patients with intermittent
exotropia become exophoric. The recommended
schedule of occlusion is as follows:
Initially, the results are evaluated after
4 months of occlusion. If the angle of deviation
is decreased, the occlusion should be continued
and assessment made every 4 months until no
further change occurs. In case, there is no
improvement after initial occlusion for 4
months, it should be discontinued.
von Noorden reports that alternate occlusion
for 3 months may be employed in lieu of surgery
with useful results in patients with small-angle
intermittent exotropia.
4. Surgical treatment
Indications for surgery
i. Surgery is advisable, when the exotropia
occurs during more than 50% of waking hours,
or causes asthenopic symptoms or when the
deviation exceeds 20.
ii. When the patient is exophoric most of the
time and becomes exotropic only two or three
times a day, surgery should be preceded by
several months of observation, since the disease
does not progress in all patients. However,
surgery should be undertaken, if during
observation patient shows one or several of
the following signs and symptoms of
progression:
• Gradual loss of fusional control as evidenced
by increasing frequency of the manifest phase
of squint.
• An increase in the size of basic deviation
(more than 20).
• Development of secondary convergence
insufficiency with asthenopic symptoms.
• Development of suppression as indicated by
absence of diplopia during manifest phase.
• Gradual deterioration of stereopsis (it is a
frequently used argument for early surgical
therapy).
260 Theory and Practice of Squint and Orthoptics
Age for surgery
There are two schools of thought:
i. Early surgery. Knap and many other workers
advocate early surgery. These workers state that,
"surgery is dictated by the amount and frequency of the exodeviation, not by the patient's
age. As long as the patient is 6 months or older,
surgery can be performed." However, they do
caution that in visually immature children a
slight undercorrection should be attempted to
prevent occurrence of mono-fixation syndrome
from consecutive esotropia.
ii. Delayed surgery. Jampolsky and a few other
workers recommend that surgery should be
delayed in visually immature infants to avoid
consecutive esotropia and occurrence of
monofixation syndrome. It is advisable that to
get good results, surgery may be delayed up to
4 years of age. Till then child should be kept
under observation to watch: Visual acuity,
convergences, and parent's observation of
frequency of squint. Further, in the interim,
binocular vision should be reinforced with prisms
base-in or minus lenses. However, in case there
is very rapid functional deterioration of fusional
control in spite of prismotherapy and orthoptics,
an early surgical therapy may be considered.
General guidelines
General guidelines adopted from the observation
of various workers are as follows:
• In true divergence excess type of exotropia, a
bilateral recession of lateral recti should be
preferred.
• In basic exotropia and simulated divergence excess
type, a unilateral lateral rectus recession and
medial rectus resection should be preferred.
However, Parks has shown that bilateral
rectus recession works for these patients also.
• In convergence insufficiency type of exotropia, a
bilateral medial rectus muscle resection may
be preferred.
• In the presence of lateral gaze inhibition (i.e. 20%
reduction in the amount of squint in right and
left lateral gaze), there is danger of overcorrection with the usual surgery especially
so in visually immature patient. Therefore, in
the presence of LGI, a bilateral lateral rectus
recession should be avoided and also, the
recession and resection done on the
nonpreferred eye should each be 1 mm less.
• In small children (visually immature patients), a
slight undercorrection should be attempted to
avoid hazards of consecutive esotropia.
• In visually mature patients, many strabismo-
logists feel that the surgeon should aim at an
overcorrection of 10D to 20D to ultimately
produce more stable results. However, it has
been observed that it is not possible to
accomplish this goal other than by pure
chance.
• Single muscle surgery is almost useless in
exotropias, it has been reported in the
literature.
Amount of surgery
The actual amount of surgery performed will
vary according to an individual surgeon's
technique. However, guidelines given in
Tables 10.6, 10.7 and 10.8 may be useful as rough
estimate of amount of surgery to be performed.
Management of associations
1. Pattern deviations
i. A-pattern exotropia (see page 299)
ii. V-pattern exotropia (see page 299)
2. Comitant vertical deviation (see page 268)
3. Dissociated vertical deviation (DVD). Though
very rare, but may be associated with
exotropia (see page 277).
Surgical results and postoperative management
After squint surgery, the eyes may be in
orthoposition, still exotropic (undercorrection)
or consecutive esotropic (overcorrection).
Depending upon the position of the eyes, the
postoperative management will be as follows:
1. Orthoposition
Undoubtedly, it is ideal to get a permanent
orthoposition, but there is always a tendency of
the eyes to diverge postoperatively. Therefore,
it is extremely important to strengthen the positive
fusional convergence with orthoptic exercises in
order to improve control of the newly acquired
bifoveal single vision.
Concomitant Esotropias and Exotropias
261
Table 10.6 Rough estimate of amount of surgery to be
performed in patients with intermittent divergent squint
of true divergence excess type
Deviation in prism Bilateral lateral
dioptres rectus recession
15 4.0
20 5.0
25 5.5
30 6.0
35 6.5
40 7.0
50 8.0
60 9.5
70 8.0 + 8 mm MR resection
in one eye
80 8.0 + 8 mm MR resection
in both eyes
Table 10.7 Rough estimate of amount of surgery to be
performed in patients with intermittent exotropia of
basic and simulated divergence excess type
Deviation in Binocular surgery Uniocular surgery
prism in mm in mm
dioptres Bilateral LR LR + MR
recession recession resection
15 4.0 4.0 3.0
20 5.0 5.0 4.0
25 5.5 6.0 4.5
30 6.0 7.0 5.0
35 6.5 7.5 5.0
40 7.0 8.0 6.0
50 8.0 9.0 7.0
60 9.5 10.0 8.0
70 8.0 + 8.0 MR resection in one eye
80 8.0 + 8.0 MR resection in both eyes
Table 10.8 Rough estimate of amount of surgery to be
performed in patients with intermittent exotropia of
convergence insufficiency type
Deviation in prism Bilateral medial
dioptres rectus resection
15 3.0
20 3.5
25 4.5
30 5.5
35 6.0
40 6.5
50 7.5
60 8.0
70 8.0 LR recession of one eye + 8.0
80 8.0 LR recession of both eyes + 8.0
Orthoptic exercises required to strengthen the
positive fusional convergence are the same as
described for exophoria (see page 226).
2. Consecutive esotropia (overcorrection)
A very large overcorrection
with gross limitation
of ocular motility noted on the very next day is
possibly due to lost or slipped lateral rectus
muscle. Under such circumstances, patient
should undergo surgery again within 24 hours.
Small to moderate (10
to 50
) overcorrection
needs to be managed depending upon the age
of the patient:
A. In adults (visually mature patients), as
described earlier, an overcorrection of 10 to 20
is desirable to ultimately achieve stable results.
• If overcorrection is more than 20 after at least
six weeks of surgery, then following non-
surgical measures should be tried during the
wait and watch period of 6 months.
– Rerfraction should be done and if hyperme-
tropia is detected, it should be fully
corrected.
– Bifocals or miotic therapy may be prescribed,
if near esotropia is more than the distance.
– Prismotherapy in the form of Fresnel
membrane prism that fully correct the
deviation should be prescribed. The prism
power should be adjusted monthly
depending upon the latest examination
results.
• Re-surgery is indicated in patients where
overcorrection of more than 20 continues
even after the above described non-surgical
therapy for a period of 6 months.
It has been recommended that in planning
second surgery, Cooper's dictum (i.e. the
decision about choice and amount of surgery
should be made as if the present patient is a
fresh case of squint) should be followed.
B. In small children (i.e. visually immature
patients), as stated earlier, the consecutive
esotropia is associated with a greater danger of
developing monofixation syndrome and
suppression amblyopia. So these patients need
a special care. Following measures should be
taken within 2 weeks of the surgery.
• Re-refraction should be done and any
hypermetropic error should be fully corrected.
• Bifocals or miotics should be prescribed, if the
deviation is greater at near.
262 Theory and Practice of Squint and Orthoptics
• Occlusion therapy. Initially, when there is no
fixation preference, alternate occlusion should
be done for a few weeks. If the child develops
moderate fixation preference, conventional
occlusion of the preferred eye should be used
till either there occurs alternate fixation or only
a mild fixation preference.
• Prismotherapy in the form of 'Press on' base-
out Fresnel membrane prism should be started
at this stage to maintain bifoveal fixation. The
prism power should fully correct the deviation
and be adjusted monthly depending upon the
latest examination results.
• Re-surgery is indicated, if the child remains
overcorrected by 15 or more in spite of the
above described non-surgical therapy.
For a re-operation, the Cooper's dictum (as
stated above) should be followed.
3. Residual exotropia (undercorrection)
i. Small residual exotropia (15
to 18
) should
be managed by following non-surgical measures:
• Optical correction. Refraction should be done
and if the patient is myopic, a full optical
correction should be ordered.
• Cycloplegics. In hypermetropic or emmetropic
patient, 1% cyclopentolate eyedrops may be
instilled twice a day to stimulate accommodative convergence. Once the alignment of the
eyes and fusion are achieved, the frequency
of instillation should be reduced progressively,
i.e. once a day, then on alternate day to every
third day. The regime may be continued for
several months till full alignment is achieved.
• Orthoptic exercises in the form of antisup-
pression exercises (see page 186) and fusional
convergence exercises (see page 227) should
be continued till the goal is achieved.
• Prismotherapy in the form of base-in prisms
that equals the undercorrection may be useful
in visually mature patients.
ii. Large residual exotropia (more than 15D to
18D) needs resurgery which can be performed
within 6–8 weeks of primary procedure. For a repeat
surgery, the planning should be done as on a
new case (Cooper's dictum). Depending upon
the type of residual exotropia and primary
procedure done, the secondary procedure can
be planned as shown in Table 10.9.
Table 10.9 Plan of secondary surgical procedures in
patients with large residual exotropia
Type of residual Primary Secondary
exotropia procedure procedure
performed required
Basic exotropia Recess-resect Recess-resect
(equal for near operation operation on the
and distance) other eye
Bilateral Ipsilateral medial
lateral rectus rectus resection and
recession lateral rectus marginal
Divergence Bilateral myotomy
excess type lateral rectus Further recession
(greater at recession or myotomies of
distance lateral recti.
than near)
Convergence Recess-resect Recession of the
insufficiency procedure virgin lateral rectus
type (greater and further recession
at near than or marginal myotomy
distance) of the already recessed
lateral rectus muscle
Criteria for success of management
The criteria for classification of excellent and
poor success in the management of exotropia
are as described below.
Excellent success
• Phoria for distance and near in the primary
position and reading position.
• Absolute convergence not less than 20 p.d. for
distance and near.
• Relative convergence not less than 15 p.d. for
distance and near.
• Unlimited near point of convergence (5 cm or
closer).
• No suppression.
• Excellent awareness of diplopia during testing
situation.
• Comfortable without asthenopic symptoms.
Failure
• Tropia at any distance or intermittent at two
of the four testing distances.
• Absolute convergence less than 10 p.d. for
distance.
• Relative convergence less than 5 p.d. for
distance and near.
• Near point of convergence less than 8 cm.
• Peripheral and foveal suppression.
• No awareness of diplopia.
• Asthenopic symptoms.
PRIMARY CONSTANT EXOTROPIA
Primary constant exotropia (Fig. 10.10) does not
occur as frequently as intermittent exotropia,
and both groups combinedly occur less
frequently than esotropias (constant exotropia,
aetiologically, may be primary, secondary,
sensory and consecutive). The number of
primary constant exotropias is small compared
to the number of secondary forms.
Clinical features
1. Time of onset
Two types of primary constant exotropias have
been described depending upon the time of
onset:
1. Primary constant, infantile exotropia. It is an
extremely rare condition with onset shortly after
birth. It has been reported that this form of
exotropia is more common in the African than in
the white race. It has been described on page 252.
2. Primary constant exotropia due to decompensated intermittent exotropia. The primary
constant exotropia almost invariably results from
decompensated intermittent exotropia, and thus
such patients usually do not possess a significant
amount of amblyopia. It has been reported that
in many patients intermittent exotropia may not
decompensate for a long period. Therefore, it has
been recommended that patients with intermittent exotropia need to be evaluated over a
period of time to ascertain whether progression
is taking place and surgery is warranted,
particularly those in whom a constant deviation
is present less than 50% of the time.
2. Fixation pattern
The patients with constant exotropia may fix
alternately, fix with one eye only or show a mild,
moderate or strong fixation preference. According
to the fixation behaviour, constant exotropia may
be classified as unilateral or alternating:
(a) Alternating exotropia
i. Fixation. In constant alternating exotropia, the
patient uses each eye alternately for fixation
(Fig. 10.10).
ii. Visual acuity. Usually, there is little or no
difference between the visual acuity of the two
eyes.
Concomitant Esotropias and Exotropias
Fig. 10.10 A patient with primary alternate divergent squint
(ADS): (A) Right exotropia while fixing with left eye; and
(B) left exotropia while fixing with right eye.
263
iii. Deviation. The angle of deviation is usually
large and tends to be equal for distance and near
fixation. The near deviation is determined by
the effect of proximal and accommodative
convergence. Very frequently there is a
secondary vertical deviation, the deviating
abducted eye being elevated.
iv. Sensory adaptations. In cases with acquired
alternating exotropia, the patients had normal
retinal correspondence and bifoveal fusion
before the deviation became constant. If normal
correspondence persists, there occurs complete
suppression of the deviating eye. However, if
ARC develops, both eyes co-operate in
binocular vision. Sometimes a form of binocular
vision is achieved whereby each half of the
visual field is perceived by the homolateral eye
while the information from the other half is
suppressed. Thus the left eye would perceive
the left half of the field but suppress the right
half, while the right eye would see the right
half and suppress the left. The fixation point
and its vicinity, in this case, is seen by the
fixating eye and is included in the suppression
area of the deviating eye.
(b) Unilateral exotropia
i. Fixation. In constant unilateral exotropia, the
same eye is used for fixation while the other is
deviated. Fixation preference may be mild,
moderate or strong:
264 Theory and Practice of Squint and Orthoptics
• In mild fixation preference, one eye is preferred,
but when it is covered, the other eye easily
takes up fixation and maintains it even when
the cover is removed from the first eye. Such
patients usually do not have a significant
amount of amblyopia.
• In moderate fixation preference, one eye is
preferred and when it is covered, the other eye
will take up fixation; but after the cover is
removed from the first eye, the other eye will
hold fixation only until the patient blinks or
changes fixation.
• In strong fixation preference, one eye is preferred
and when it is covered, the other eye will take
up fixation, but only as long as the cover is
left over the first eye.
• In unilateral fixation, only one eye is preferred
and when it is covered, the other eye does not
take up fixation but makes irregular jerky
movements, suggesting loss of central fixation
and a deep amblyopia.
ii. Deviation is usually large. In patients with
long-standing neglected deviations, anatomic
changes may occur in the contracted muscles.
iii. Sensory adaptations. There is marked
suppression in the deviating eye, but amblyopia
is less severe than in esotropia. ARC may be
present but is of little importance since
suppression prevails. Since the majority of
unilateral exotropias are acquired, most of the
patients have had normal retinal correspondence previously.
Associations
Primary constant exotropia may be associated
with:
• A- or V-pattern (Fig. 10.11) with or without
oblique muscle by function
• Comitant vertical deviation muscle depth
function
• Dissociated vertical deviation (DVD)
Clinical evaluation
The aim of clinical evaluation is to diagnose type
of deviation and to assess potential for binocular
single vision. The complete clinical evaluation
should be carried out in each case of strabismus.
Points pertinent to the evaluation of primary
constant exotropia are similar to those described
for the intermittent exotropia.
Treatment
The treatment of constant exotropia is almost
always surgical. Orthoptic treatment is given
both preoperatively and postoperatively, if
fusion ability can be demonstrated. Any patient
over 6 months of age can be taken for surgery.
The type and amount of surgery to be
performed is similar to that for intermittent
exotropia.
SENSORY EXOTROPIA
Definition
It refers to unilateral exotropia that develops as
a result of poor visual function in one eye.
Fig. 10.11 Nine gaze photographs of a patient with alternate divergent squint with V-pattern with inferior oblique over action
(IOOA).
Concomitant Esotropias and Exotropias
Fig. 10.12 Nine gaze photographs of a patient with left sensory exotropia.
265
Etiopathogenesis
Sensory exotropia results secondary to some
sensory deficit such as anisometropia, unilateral
cataract, unilateral aphakia, corneal opacity,
optic atrophy, macular lesion and any other
organic cause of unilateral loss of vision.
It has been reported that both infants and
young adults with poor vision in one eye develop
sensory exotropia and the older children tend to
develop a sensory esotropia. The mechanisms
and theories about development of sensory
esotropia and exotropia have been described on
page 251.
Clinical features
1. Monocular visual loss due to any cause is
always associated.
2. Deviation is unilateral and constant and
involves the eye with poor vision (Fig. 10.12).
Treatment
• Cosmetic surgery is the treatment for most
sensory exotropias. However, some scope of
functional recovery may be there in children
with sensory exotropia due to anisometropia
including unilateral aphakia.
• Choice of surgery for sensory exotropia is
usually recess-resect operation on the same eye.
In large exodeviation, one can recess lateral
rectus up to 10 mm and can resect medial rectus
also up to 10 mm. Though, it may result in
limitation of horizontal movements in the
operated eye.
• Adjustable suture surgery may be preferred
in patients above 10–11 years of age with sensory
exotropia.
CONSECUTIVE EXOTROPIA
Consecutive exotropia refers to occurrence of
exotropia in an eye which was previously
esotropic.
Clinical types
It has been reported to occur under following
two clinical situations:
1. Surgical overcorrection of esotropia may
result in consecutive exotropia (Fig. 10.13).
2. Spontaneous consecutive exotropia is change
of esotropia into exotropia without exogenous
mechanical factors or an acquired paralysis of
medial rectus muscle. Spontaneous consecutive
exotropia is known to occur more commonly
under following circumstances:
• Esotropia with poor vision in the deviating eye.
• Infantile esotropia associated with a high
hypermetropia.
Treatment
1. Refractive error, if any, kind should be
corrected.