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166 Theory and Practice of Squint and Orthoptics
functional development. General debility,
psychological instability, over work and worry
may be the precipitating factors.
2. Refractive errors. Convergence insufficiency
may be associated with uncorrected high
hypermetropia and myopia. Diseases of
accommodative convergence mechanism result
in convergence insufficiency in such patients as
follows:
• High hypermetropes (more than 5D) usually
make no effort to accommodate and thus there
is deficient accommodative convergence as
well.
• Myopes may not need accommodation and
thus lack accommodative convergence.
• Patients who have worn too full a plus
spherical correction may also exert less
accommodation and thus less accommodative
convergence.
3. Presbyopia. With the advent of presbyopia,
near point of eye recedes and so there is less use
of convergence. Neglect of presbyopia may lead
to fixation of this anomaly.
On the other hand, patients may also develop
convergence insufficiency with the first time use
of presbyopic correction. This has been
explained by the fact that the relief of sustained
accommodative effort afforded by the use of
presbyopic correction causes a decrease of
accommodative convergence.
4. Muscular imbalances. Extraocular muscular
imbalances in the form of exophoria,
intermittent exotropia and vertical muscle
imbalances, if neglected for a long time may be
associated with convergence insufficiency.
5. Consecutive convergence insufficiency may
occur following either recession of medial recti
or resection of lateral recti muscles.
Clinical features
Convergence insufficiency becomes a clinical
problem in children with increased school work,
prolonged periods of reading, desk workers and
percision workers. It is usually not a problem in
farm and manual labour workers.
Symptoms of convergence insufficiency are
similar to that of heterophoria and in general
the term asthenopia is used to denote the
symptom complex. Unsuitability of the glasses
is the most frequent complaint of patients using
glasses and having asthenopic symptoms. Such
patients change their refractionist and glasses
frequently without any satisfaction. Asthenopic
symptoms may be grouped as given below.
1. Symptoms of muscular fatigue
These result due to continuous use of the
neuromuscular power and are usually marked
with near work. These include:
• Eye strain and a sensation of tension in and
around the globes is a common complaint of
such patients.
• Headache and eye ache after prolonged use of
eyes especially for near work, which are
relieved, when the eyes are closed for a while.
Some patients may show even migrainous
tendencies.
• Difficulty in changing the focus from distant to
near objects.
• Itching, burning and soreness of eyes and even
hyperaemia of the nasal half of the conjunctiva
may occur after prolonged close work.
2. Symptoms due to failure to maintain binocular
vision
• Blurred near vision and crowding of words
while reading.
• Intermittent crossed diplopia for near vision
under conditions of fatigue is not uncommon.
• Characteristically, one eye will be closed or
covered while reading to obtain relief from
visual fatigue.
Diagnosis
Diagnosis of convergence insufficiency is
confirmed by:
1. Remote near point of convergence (NPC).
Convergence insufficiency is said to exist, if NPC
is more than 10 cm from the baseline.
2. Decreased fusional convergence for near.
When measured on synoptophore, the convergence insufficiency is said to exist, if there is
difficulty in attaining 30° of convergence.
3. Prism convergence is low but prism diver-
gence is normal.
4. Exophoria at near with orthophoria at
distance may occur. However, convergence
insufficiency may be associated with orthophoria and even exophoria.
167Anomalies of Convergence, Divergence and Accommodation
5. Near point of accommodation (NPA) is
normal and corresponds to the age of the
patient. However, measurement of NPA is
essential in each case to diagnose and manage
patients suffering from a combined insufficiency
of convergence and accommodation. Further,
rarely accommodative spasm may occur, if
voluntary accommodation and convergence are
stimulated in an effort to overcome the
convergence insufficiency.
Differential diagnosis
Convergence insufficiency needs to be differentiated from the following conditions presenting
with almost similar symptoms.
1. Convergence insufficiency versus convergence
paralysis
• In convergence paralysis, there is total lack of
ability to overcome any amount of base-out
prism; while in convergence insufficiency
several dioptres of convergence amplitude can
be demonstrated.
• On receiving a convergence impulse, a patient
with convergence paralysis will show
pupillary constriction but inability to
converge; in a patient with convergence
insufficiency, pupillary constriction will occur
while converging on an approaching target,
followed by dilation of the pupil, when
convergence can no longer be maintained.
2. Convergence insufficiency versus accommodative effort syndrome
• Usually an exophoria at near is associated
with convergence insufficiency, while patients
with accommodative effort syndrome have
esophoria.
• Convergence insufficiency is helped by the
–3D test, which compensates for the lack of
good fusional convergence; while a patient
with accommodative effort syndrome breaks
into a tropia during this test.
• Plus lenses will worsen the convergence
insufficiency due to relaxation of accommodative convergence, while they will improve
the symptoms in the accommodative effort
syndrome for the same reason.
Treatment
Convergence insufficiency has an excellent
prognosis in the majority of cases. Children are
treated, when fusional vergences are poor and
the patient is showing signs of becoming
exotropic. Adults with this condition receive
treatment only in the presence of symptoms.
Treatment of convergence insufficiency includes:
optical treatment, orthoptic treatment, prismotherapy and surgery.
1. Optical treatment
Proper refraction should be carried out and the
correct glasses should be prescribed for any
associated refractive error. Myopes are given full
correction and hypermetropes undercorrection
to stimulate their accommodation which will
simultaneously stimulate convergence. In adults
above the age of 40 years, proper presbyopic
correction should also be done.
2. Orthoptic treatment
Aim of orthoptic exercises is to improve the
binocular convergence and to increase the
amplitude of fusional convergence. ‘Vision
therapy’. The term used for orthoptic treatment
includes:
A. Conventional or non-computerised exercises for:
• In-office vision therapy, and
• Home vision therapy
B. Computerised orthoptic exercises for:
• In-office vision therapy, and
• Home vision therapy
Note. Conventional, i.e. non-computerised
excercises are described here. For computerised
exercises see page 154.
Conventional or non-computerised exercises
Orthoptic treatment for convergence insufficiency is by and large same as for exophoria and
includes the following exercises:
(a) Exercises to improve near point of
convergence
i. Advancement exercises (see page 228).
ii. Jump convergence exercises (see page 228).
iii. Pencil dips: This exercise involves dipping the
target (pencil) in and out of your field of
vision to challenge your convergence ability.
168 Theory and Practice of Squint and Orthoptics
iv. Pencil push-ups: This is one of the most
commonly prescribed exercises for convergence insufficiency. Here's how it's done:
• Hold a small target (like a pen or pencil)
vertically at arm's length in front of nose
and focus on the target.
• Slowly bring the target closer to your nose
while maintaining clear and single vision.
• Stop the moment you notice double vision
or the target splitting into two.
• Hold the target at that distance for a few
seconds, and then move it back to arm's
length.
• Repeat this process for about 10–15
repetitions, a few times a day.
iv. Brock string exercise: The Brock string is a
simple tool that can help train convergence
and depth perception (Fig. 7.4).
• Attach a colored string (around 3–4 feet
long) to a stationary object at eye level
(Fig. 7.4A).
A
B
Fig. 7.4: Brock String exercise (A), and its three steps (B)
• Place the other end of the string on the tip
of your nose (Fig. 7.4A).
• Focus on the string, and you should see a
series of colored beads along the string.
• As you focus on the string, the beads
should appear to merge into a single bead.
This indicates that your eyes are
converging properly.
• Gradually move the end of the string closer
to your nose and repeat the process.
(b) Exercises to increase amplitude of fusional
convergence
i. Convergence exercises with prisms (see page
227).
ii. Convergence exercises using synoptophore (see
page 227).
iii. Exercises using convergence card. Convergence
card consists of dots on either side; so also
known as physiologic dot card. On one side
of the card, dots are coloured red and on the
other side blue. Dots identical in size are in
the same place on each side of the card and
these are of three sizes—large, medium and
small.
To perform the exercise, the card is put in front
of the patient's eyes with one end of the card
resting on his/her nose, with the large dots
farthest away, so that he/she will see the red dots
with one eye and the blue with the other eye.
The patient is instructed to look at the large dots
and to see them fused or blended together, then
the middle dots and finally the smallest ones.
The patient must be aware of heteronymous
physiologic diplopia on those dots between his/
her eyes and the fused ones; and homonymous
physiologic diplopia on those beyond the fused
one.
With the use of convergence card, there is a
great deal of retinal rivalry. If the patient is
unable to do the exercises as instructed above,
it may be easier for him/her, if the three dots are
connected with a black line on both sides of the
card (Fig. 7.5). Now, when fixating on the large
size dots, he/she should see the lines as . When
he/she is able to fuse the large dots easily, he/
she may then fixate on the middle size dots and
see the black lines as X. Lastly, he/she should
fixate the small size dots and see the black lines
as .
Fig. 7.5 Convergence card.
169Anomalies of Convergence, Divergence and Accommodation
3. Prismotherapy
When all the exhaustive orthoptic exercises fail,
then prismotherapy may be tried to relieve
symptoms.
• Base in prism reading glasses or bifocals with
prism in the lower segment are useful as
relieving prisms.
• Relieving prisms and bifocals in young age
should be avoided.
iv. Physiologic diplopia exercise using stereogram
in the uncrossed position (see page 227).
v. Convergence exercise using diploscope (see
page 149).
(c) Training of voluntary convergence
It is very helpful, if the patient is intelligent and
co-operative. It aims at developing the control
of the position of eyes. Patient is made to
understand physiological diplopia which he/she
practices. If a finger is brought in the field of
vision while the patient is fixing a distant light,
there will appear two fingers. Now, if the patient
fixes at the finger, then there will appear two
lights at the distance. While the finger is moved
to and fro, the distance between the lights
increases or decreases. Patient is asked to
maintain the two lights apart as long as possible.
The finger may again be brought in, if the two
lights become single as soon as the finger is
removed. This exercise is completed, when the
patient is able to double the lights without the
aid of the finger. Development of voluntary
convergence goes a long way in relieving
symptoms.
(d) Relaxation exercises
Relaxation using relative negative convergence
may be carried out after the treatment by any of
the following methods:
i. Stereogram in crossed position (see page 225).
ii. Divergence with prisms (see page 225).
iii. Synoptophore exercises (see page 225).
Criteria for good orthoptic management
• Patient should be symptom free.
• There should be good binocular convergence.
• Voluntary convergence should be possible
easily.
• Patient should have good fusional reserves.
4. Surgical treatment
As a last resort, when all other measures fail,
especially when convergence insufficiency is
associated with a large exophoria at near vision,
medial rectus muscle resection can be performed
in one or both eyes. In some cases, exophoria at
near fixation tends to recur.
Convergence insufficiency treatment trial
Convergence insufficiency treatment trial
(CITT) was conducted to compare three forms
of vision therapy with office-based placebo
therapy:
• Office-based vision therapy with a trained therapist
along with home reinforcement. Children in this
group came to the office once per week for a
60-minute therapy session with a trained
therapist. During these sessions, the children
worked on 4–6 procedures designed to
improve the ability to converge the eyes. The
children in this group also did home therapy
for 15 minutes, 5 days per week to practice
the procedures learned during the office visits.
• Home-based pencil push-ups therapy. In this
group, the child had to follow a small letter
on a pencil as the pencil was moved toward
the bridge of his nose. His goal was to keep
the letter clear and single, but to stop if the
letter became double. The child was told to
try and get the pencil closer and closer to the
bridge of his nose each day. This was practiced
for 15 minutes, 5 days per week.
• Home-based computer vision therapy and pencil
push-ups. In this group, the child was given
complex exercises using a computer program
plus pencil push-ups.
• Office-based placebo therapy. This group was
given placebo vision activities designed to
simulate office-based therapy.
170 Theory and Practice of Squint and Orthoptics
CITT concluded that office-based vision therapy
with a trained therapist plus at-home reinforcement was most effective in treating CI in
children 9 to 17 years old.
CONVERGENCE INSUFFICIENCY
ASSOCIATED WITH ACCOMMODATIVE
INSUFFICIENCY
Convergence insufficiency in some patients may
be secondary to accommodation insufficiency.
Therefore, before treating the patient for a
functional convergence insufficiency, it is
important to rule out associated accommodation
insufficiency.
Etiology
Secondary convergence insufficiency associated
with primary accommodation insufficiency has
been reported to occur in following conditions:
1. Early Adie's syndrome
2.Sequelae to head trauma, particularly
posterior occipital or whiplash injury.
3. Subclinical viral encephalopathies.
4. Infectious mononucleosis
5. Diphtheria
6. As a conversion reaction.
Clinical features
1. Symptoms of the patients are similar to those
of functional convergence insufficiency.
2. Near point of convergence (NPC) is reduced.
3.Near point of accommodation (NPA) is
reduced drastically.
4.Accommodative convergence/accommodation (AC/A) ratio may be low or even
absent.
Treatment
1. Orthoptic exercises alone are usually not
much effective. Exercises need to be combined
with reading glasses.
2. Plus lenses for reading and base-in prism is
the treatment of choice. The reading spectacle
prescription should be titrated according to
patients need. The minimal power necessary to
achieve comfortable vision should be prescribed. Fresnel membrane prisms glued on glass
lenses in the lower segment of bifocals may be
useful, since a frequent change may be necessary
before the final adjustment is made. Alternatively, two piece executive bifocals with
decentered plus lenses for prism power in the
lower half may be prescribed.
3. Surgery is usually not indicated for this
condition. However, it has been reported that
resection of both medial rectus muscles followed
by prescription of bifocal adds may be helpful
in untreatable cases.
CONVERGENCE PARALYSIS
Convergence paralysis refers to a total lack of
ability to overcome any amount of base-out
prisms. It is an uncommon entity and should
not be confused with functional convergence
insufficiency which is very common.
Etiology
Convergence paralysis occurs secondary to
some organic diseases of the brain in the region
of corpora quadrigemina or the nucleus of third
cranial nerve. The organic brain lesions reported
to be associated with convergence paralysis are
as follows:
• Head injury
• Encephalitis
• Disseminated sclerosis
• Tabes dorsalis
• Narcolepsy
• Tumours
Clinical features
Convergence paralysis is characterized by
following features:
1. Convergence is completely absent. There is
acute onset of convergence failure.
2. Exotropia and crossed diplopia occur on
attempted near fixation only.
3. Adduction is normal.
4. Accommodation is usually normal. But in
some cases it may be reduced or even absent.
Parinaud's syndrome refers to convergence
paralysis associated with vertical gaze paralysis.
Pretectum-posterior commissure syndrome
(dorsal midbrain syndrome) which is commonly
caused by tumour in the pineal region includes:
• Convergence paralysis
171Anomalies of Convergence, Divergence and Accommodation
• Vertical gaze paralysis
• Pupillary areflexia to light with light near
dissociation.
• Bilateral fourth nerve paralysis may be present
sometimes.
• Lid retraction may also occur in some patients.
Diagnosis
Bielschowsky's criteria for diagnosis of the
convergence paralysis include: (1) evidence of
intracranial disease, (2) history of sudden
onset of crossed horizontal diplopia at near
fixation, (3) reproducible findings on subsequent examinations and (4) preservation of
accommodation and pupillary reaction on
attempts to converge.
Differential diagnosis
Convergence paralysis can be differentiated
from functional convergence insufficiency
by use of base-out prisms. A patient with
convergence paralysis will immediately have
diplopia, while in convergence insufficiency
several dioptres of convergence amplitude can
be demonstrated.
Treatment
1. Base-in prisms are prescribed at near to
alleviate the diplopia at near.
2. Plus lenses with base-in prisms may be required
in patients having weakness of accommodation.
3. Occlusion of one eye at near may be indicated
in patients where it is not possible to restore
comfortable single binocular vision.
4. Eye muscle surgery is contraindicated in this
condition.
CONVERGENCE SPASM
Convergence spasm refers to a condition
characterized by intermittent episodes of maximal convergence usually associated with spasm
of accommodation.
Etiology
1. Functional causes. It has been reported that
in most of the cases, convergence spasm is
functional in origin. It occurs in patients with
hysteria or neurosis.
2. Organic causes. Rarely convergence spasm
may be secondary to some underlying organic
lesion. It has been reported to occur after head
trauma, encephalitis, tabes, pituitary adenomas,
posterior fossa neurofibroma and Arnold-Chiari
malformation.
Clinical features
In most of the cases, the condition is episodic.
In between the attacks, patients are normal.
During the episode of convergence spasm, a
patient may exhibit following clinical features:
1. Extreme convergence. Eyes may be fixed in a
position of extreme convergence resembling
bilateral abducens palsy.
2. Homonymous diplopia may be experienced.
Patient may give history of intermittent diplopia.
3. Blurring of vision. During the attack, patient
may have blurred vision for near due to
associated spasm of accommodation. Patient
may come with a complaint of difficulty in
reading.
4. Miosis. Pupils usually become miotic, as a part
of near reflex.
5. Induced myopia to the tune of 6D (confirmed
by retinoscopy) has been reported due to
associated spasm of accommodation. Thus,
during the attack, patient may also have a
reduced distance visual acuity.
Psychiatric examination may reveal the
underlying hysteria and neurosis in many cases.
Management
Neurological evaluation. Organic lesions are a
rare cause of spasm of convergence; however,
each patient should undergo detailed neurological evaluation to rule out associated
condition, if any.
Treatment of functional spasm of convergence
includes:
1.Prolonged atropinization with plus lenses in lower
segment of bifocals for near work may be
required to break the cycle.
2.Alternate monocular occlusion may be
considered as an alternative to atropinization.
3.Psychiatric work-up and therapy is useful as a
long-term measure.
172 Theory and Practice of Squint and Orthoptics
DIVERGENCE
As mentioned earlier, divergence refers to
disjugate but symmetrical and simultaneous
outward rotation of the two eyes from a given
position. It is unknown whether voluntary
divergence exists. Certainly, it is possible to relax
one's convergence voluntarily and to produce
in this way a more divergent position of the eyes.
Thus, from clinical point of view, the only
significant form of divergence is fusional
divergence.
Fusional divergence
Fusional divergence, also called negative
fusional convergence, is the divergence that is
produced (like the positive fusional convergence)
to ensure that similar retinal images are
projected onto corresponding retinal points of
two eyes. It occurs without a change in refractive
state of eye and is initiated by a binasal retinal
image disparity. In other words, fusional
divergence implies a responsiveness to
disparate stimuli lying outside of Panum's
fusional area. Similar to fusional convergence,
it is a kind of optomotor reflex and includes:
1. Positive fasional divergence: It is the ability
of the eyes to move outward to maintain
binocular single vision when the eyes focus from
near to distant object. It is measured using base
out prism test.
Base-out prism test (BO Test): In this test, baseout prisms are placed in front of one eye while
the patient fixates on a near target. The examiner
gradually increases the prism power until the
patient reports seeing double or experiences a
break in fusion. The amount of prism required
to break fusion provides information about
positive fusional divergence.
When fusional divergence amplitudes are
measured with a prism bar, the normal range is
4D to 6D at distance and 8D to 12D at near. As
discussed earlier, in the case of fusional
convergence, the end point of the amplitude
(i.e. the point of maximal convergence) is
marked by an identical phenomenon, that is,
blurring of vision both for distance and near.
However, in fusional divergence, the end point
of amplitude differs in character for near
(blurring of vision) and distance (double vision)
as follows:
• End point of amplitude of fusional divergence for
distance: Beyond the maximal limit of fusional
divergence, there occurs diplopia (end point).
• End point of amplitude of fusional divergence for
near: In near vision, as we know, the eyes are
accommodated and also converged. Under
these circumstances, when measuring the
amplitude of fusional divergence beyond the
limits of maximal fusional divergence the
accommodative convergence is relaxed to
prevent retinal disparity. But along with the
relaxation of accommodative convergence, the
accommodation is also relaxed resulting in
blurring of vision (end point).
2. Negative fusional divergence (base-in
divergence): Negative fusional divergence is the
ability of the eyes to move inward (converge) to
maintain single binocular vision when the eyes
are initially diverged for a distant object, and
then the target moves closer. This type of
divergence is less commonly assessed but is still
important for binocular vision.
• Base-in prism test (BI test): Similar to the BO
test, the BI test involves the use of base-in
prisms. Prisms are introduced in front of one
eye, and the patient fixates on a distant target.
The prism power is gradually increased until
the patient reports seeing double or
experiences a break in fusion. The amount of
prism required to break fusion indicates
negative fusional divergence.
Convergence to divergence ratio (Con/D): This
ratio represents the balance between convergence
and divergence abilities. It is calculated by
comparing the amount of convergence
(measured in prism diopters) that a person can
achieve to the amount of divergence. A Con/D
ratio of 3:1 is often considered normal.
Divergence facility test: Divergence facility
refers to the speed and accuracy with which the
eyes can move outward to diverge. This test
typically involves a flipper with base-out prisms.
The patient alternates between different
divergence targets with varying prism powers
while maintaining fusion. The speed and ease
with which the patient can maintain fusion
provide information about their divergence
facility.
173Anomalies of Convergence, Divergence and Accommodation
Measurement of amplitude of divergence
See page 124.
ANOMALIES OF DIVERGENCE
DIVERGENCE INSUFFICIENCY
Divergence insufficiency is not synonymous
with divergence paralysis, but is a separate
clinical entity.
Etiology
Exact etiology is not known. It has been assumed
that perhaps in divergence insufficiency, a preexisting esophoria at distance fixation caused
by an anomalous position of rest becomes
manifest.
Clinical features
Characteristic features are as follows:
1. Esodeviation. Intermittent or constant eso-
deviation is much larger at distance than
near. Usually, patients maintain the fusion
at near. Esodeviation is comitant in all fields
of gaze.
2. Ductions and versions are normal in all the
directions.
3. Fusional divergence is markedly reduced both
at distance and near fixation.
4. Absence of any neurologic disease (e.g.
divergence paralysis).
Treatment
1. Orthoptic exercises for divergence insufficiency
i. Pencil/pen divergence: This exercise helps
strengthen the eye muscles responsible for
diverging. It is the opposite of the pencil
push-up exercise used for convergence
insufficiency.
• Hold a pencil or pen vertically at arm's
length, with the tip at your eye level.
• Focus on the tip of the pencil.
• Slowly move the pencil away from your
nose while maintaining clear and single
vision.
• Stop if you experience double vision and
then bring the pencil back closer to your
nose.
• Perform this exercise for about 10–15
repetitions, several times a day.
ii. Brock string exercise: The Brock string (Fig. 7.4)
can be adapted to train divergence abilities
by using colored beads that appear to move
apart.
• Attach a colored string (around 3–4 feet
long) to a stationary object at eye level.
• Hold the other end of the string to your
nose.
• Focus on the string, and you should see a
series of colored beads along the string.
• As you focus on the string, the beads
should appear to move further apart,
indicating that your eyes are diverging
properly.
• Gradually move the end of the string
closer to your nose and repeat the process.
iii. Near-far target switching: This exercise helps
improve the coordination between near and
far vision.
• Hold a target (e.g. a finger or small object)
at arm's length, focusing on it.
• Without moving your head, shift your
focus to a distant object in the background.
• Alternate between the near and far targets,
working on the smooth transition of your
gaze.
2.Computer based exercises for divergence
insufficiency
Some computer-based vision therapy programs
offer exercises specifically designed to improve
divergence abilities. These programs often
involve tracking moving objects that require
your eyes to diverge correctly. Computer based
exercises and tools that may help with
divergence insufficiency include:
i. Interactive vision therapy software: Several
vision therapy software programs are
designed to improve eye coordination and
alignment. These programs typically offer
exercises that challenge the eyes to diverge
correctly. Some examples include:
• Vectograms: These computer-generated
images create an illusion of depth, and the
patient is asked to identify specific
patterns within the images while
maintaining proper eye alignment.
• Brock string simulation: Some software
programs simulate the brock string
exercise, which involves tracking colored
174 Theory and Practice of Squint and Orthoptics
beads on a string and working to keep
them single or separated at different
distances.
ii. 3D and virtual reality (VR) exercises: Three-
dimensional and VR exercises can provide
an immersive experience to improve
divergence abilities. These exercises often
involve interacting with 3D objects or virtual
environments that require proper eye
coordination.
iii. Online vision therapy platforms: Some online
platforms offer comprehensive vision
therapy programs, including computerbased exercises tailored to address specific
vision problems like divergence insufficiency.
These programs are typically supervised by
eye care professionals.
iv. Interactive games: There are video games and
apps designed to improve eye coordination
and divergence skills. These games may
involve tracking moving objects or
completing visual tasks that require precise
eye movements.
3. Prismotherapy. Divergence insufficiency is a
self-limiting condition. However, to alleviate the
patient of symptoms, prism base-out is prescribed
to provide comfortable single vision at distance.
Prism power is decreased stepwise in months
and ultimately discarded.
4. Surgical treatment. In the form of resection
of both lateral rectus muscles is indicated, rarely
when the prismotherapy fails.
DIVERGENCE PARALYSIS
Divergence paralysis is a rare entity characterized by a sudden onset esotropia at distance
fixation and a homonymous diplopia.
Etiology
Divergence paralysis may be associated with a
head trauma or other neurologic diseases such
as encephalitis, tabes, disseminated sclerosis,
vascular disorder, neoplasm and raised
intracranial pressure.
Clinical features
Clinical features of divergence paralysis are
similar to divergence insufficiency except that
it is of sudden onset and usually associated with
some organic neurologic diseases.
Differential diagnosis
1. Unilateral or bilateral sixth nerve palsy.
Clinically, a paralysis of fusional divergence is
differentiated from the bilateral sixth cranial
nerve paralysis by the fact that in the former, at
a given distance, the deviation is comitant and
that the distance between the double images
remains the same irrespective of the position of
the object of regard, as it is moved laterally in
the radius of a circle with the patient at the
centre. This observation indicates that perhaps
a separate divergent centre exists. However, still
no specific midbrain or central nervous system
centre has been proved to be divergence centre
that abduction is completely normal bilaterally.
2. Convergence spasm may also be confused with
divergence paralysis because in both the
conditions patients have uncrossed diplopia at
distance fixation. However, in convergence spasm
visual acuity is reduced due to induced myopia
and the divergence fusional range is normal.
Management
A thorough neurologic work-up is required for
any associated disease. However, divergence
paralysis has no localizing significance for the
neurologist. Further, despite the association of
neurologic diseases, mostly divergence paralysis
is self-limiting and disappears within 5 to 6
months. During this period, prismotherapy as
described for divergence insufficiency is
required. Bilateral lateral rectus resection may
be indicated in some cases where divergence
paralysis persists beyond 6 months.
ACQUIRED MOTOR FUSION DEFICIENCY
Acquired motor fusion deficiency refers to a
combined deficiency of the fusional convergence
and fusional divergence.
Etiology
It has been assumed that, perhaps, a midbrain
lesion accounts for the acquired motor fusion
deficiency. The lesions reported to be associated
with this rare entity are as follows:
• Closed head trauma
• Cerebrovascular accidents
• Intracranial tumours
• Brain surgery
Clinical features
1.Asthenopia. Most patients complain of severe
asthenopic symptoms.
2.Diplopia is usually intractable and variable, i.e.
may be crossed at one moment and uncrossed
at another.
3.Fusional amplitudes (convergence as well as
divergence) are either markedly decreased or
completely absent.
4.Sensory fusion and stereopsis are intact during
the brief moments and that such patients may
be able to superimpose the double images.
5.Accommodation range may be decreased.
Differential diagnosis
Acquired motor fusion deficiency needs to be
differentiated from following conditions:
1.Combined convergence and accommodation
deficiency (see page 170).
2.Motor fusion deficiency in adults due to
prolonged unilateral use of the eye as seen
with unilateral cataract or untreated unilateral
aphakia.
3.Malingering: Some patients may malinger for
diplopia-like acquired motor fusion deficiency
following work-related trauma to get compensation. Measurement of fusional amplitudes
with a rotatory prism helps in differentiating
the two conditions.
Treatment
Treatment of this condition is usually frustrating.
Prisms cannot be employed because of frequent
adjustments for near and distance. The only
way to get relief from symptoms is unilateral
occlusion. Infrequently, a spontaneous recovery
may occur.
ACCOMMODATION
ACCOMMODATION AND RELATED TERMS
Accommodation
As we know that in an emmetropic eye, parallel
rays of light coming from infinity are brought
to focus on the retina, with accommodation at
rest. Our eyes have been provided with a unique
mechanism by which we can even focus the
diverging rays coming from a near object on the
175Anomalies of Convergence, Divergence and Accommodation
Fig. 7.6 Effect of accommodation on divergent rays entering
the eye.
retina in a bid to see clearly (Fig. 7.6). This
mechanism is called accommodation. In it, there
occurs increase in the power of the crystalline
lens.
Far point, near point, range and
amplitude of accommodation
The nearest point at which small objects can be
seen clearly is called near point or punctum
proximum and the distant (farthest) point is
called far point or punctum remotum. The
distance between the near point and the far
point is called range of accommodation. The
difference between the dioptric power needed
to focus at near point (P) and to focus at far point
(R) is called amplitude of accommodation (A). Thus,
A = P – R.
Far point and near point of the eye vary with
the static refraction of the eye. In hypermetropic
eye, far point is virtual and lies behind the eye,
while in myopic eye, it is real and lies in front of
the eye (Fig. 7.7). In an emmetropic eye, far point
is at infinity and near point varies with age;
being about 7 cm at age of 10 years, 25 cm at the
age of 40 years and 33 cm at the age of 45 years.
Thus the amount that the eye can alter its
refraction is greatest in childhood and slowly
decreases until it is lost in middle age.
Amplitude of accommodation in dioptres as
function of the age, as studied by Duane is
depicted in Fig. 7.8.
ASSESSMENT OF ACCOMMODATION
See page 125.
AGE-RELATED CHANGES IN ACCOMMODATION
As discussed earlier, in an emmetropic eye, far
point is infinity and near point changes with age,
being about 7 cm at the age of 10 years, 25 cm at
the age of 40 years, 33 cm at the age of 45 years