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276 Theory and Practice of Squint and Orthoptics
4. Associated horizontal deviation in primary
position. PSOO is commonly associated with
either comitant exotropia (more common) or
esotropia, usually of A-pattern (<10 PD in
unilateral and >20 PD in bilateral SOOA). By
contrast, SSOO is usually not associated with
any form of concomitant deviation.
5. Associated vertical deviation in primary
position is usually absent in PSOO. While
vertical deviation (hypotropia) is characteristic
of SSOO. Bilateral SOOA is associated with a
small or no hypotropia in primary position, since
the bilateral vertical deviations cancel each
other. However, reversing hypotropias in side
gaze are typical, with a right hypotropia in left
gaze and a left hypotropia in right gaze.
6. Head tilt in the direction of action of paralysed
inferior oblique is typically present in patients
with SSOO, when the onset is after 6 years of
age (after visual maturity); while it is usually
absent in patients with PSOO. Head tilting will
not cause any difference in the amount of
deviation in primary SOOA.
7. Associated incyclodeviations. Objective
incyclodeviation, as evidenced by a disturbed
relationship of the optic disc with foveola, can
be demonstrated in both patients with primary
as well as secondary superior oblique overaction. However, subjective incyclodeviation (as
demonstrated by double Maddox rod test, Hess
screen test, the major amblyoscope or the
Lancaster red-green test) is typically present in
patients with SSOO, when the onset is after
6 years of age, but is absent in patients with
PSOO.
8. Forced duction test is usually positive in both
primary as well as secondary superior oblique
overaction. An 'edge' of resistance is felt as the
eye is passively rotated with forceps up and in
(into the field of antagonist inferior oblique).
Differential diagnosis
1. Brown syndrome can be differentiated from
primary SOOA, on a clinical basis as below:
• An ability to elevate the paretic eye in
adduction effectively rules out Brown
syndrome.
• In contrast to SOOA where hypotropia is
maximum in downgaze, Brown syndrome is
associated with a restriction of elevation thus
causing a hypotropia that is greatest in
upgaze.
• ‘A’ pattern in SOOA, while there is ‘V’ pattern
in Brown syndrome. FDT +ve in Brown
syndrome.
2. Inferior oblique paresis. There is ipsilateral
SSOOA in which unlike PSOOA, there is
positive head tilt test, hypotropia is greatest
when patient looks up and in. The deviation
worses in the gaze away from paretic eye. In IO
palsy, the deviation worses with tilt toward the
paretic eye because intorsion is impaired.
Treatment
In a patient with clinically significant ocular
deviation or A-pattern associated with bilateral
superior oblique overaction, a bilateral superior
oblique weakening procedure is indicated,
which can be accomplished as follows:
1. Superior oblique tenotomy and tenectomy: It
is indicated for treating ‘A’ pattern strabismus
and can correct 20 PD or more of A-pattern in
the primary position and up to 45 PD in
downgaze. The amount of correction achieved
depends mostly on the size of preoperative
pattern and the amount of SOOA. This can be
done either nasally or temporally to the superior
rectus muscle. Effectivity of superior oblique
tenotomy increases, if performed closer to the
trochlea; therefore, nasally performed operation
gives more effect. This usually causes postoperative SO palsy and tortional diplopia in
patients with fusion.
2. Posterior tenectomy of superior oblique
(PTSO): The anterior fibres of SO tendon are
responsible for torsion, whereas the posterior
fibres are implicated in downward rotation and
abduction. This procedure is preferred over
tenotomy in patients with bifoveal fusion
because negligible extorsion is induced. This
surgery can correct moderate A-pattern up to
20 PD with SOOA.
3. Superior oblique lengthening by insertion of a
silicone expander or a non-absorbable suture is
also an effective procedure. In fact several
surgeons have proposed more controlled
weakening by superior oblique tendon expander
(SOTE) surgery (rather than tenotomy) in patients
277Vertical Strabismus and Cyclodeviations
with bifixation and normal stereopsis to eliminate
the complications like torsional diplopia or
symptoms of secondary superior oblique palsy
with head tilt observed with simple tenotomy.
The weakening effect is graded by varying the
length of the silicone that bridges the gap
between the cut ends of the tendons. The spacer
lengthens the tendon without altering the
muscle mechanics at its insertion . This corrects
‘A’ pattern from 20 to 55 PD and also the SOOA
associated with skew deviation.
Recommended length of spacer according to the
magnitude of SOOA is as below.
• +1 overaction: 4 mm
• +2 overaction: 5 mm
• +3 overaction: 6 mm
• +4 overaction: 7 mm
Note. For surgical techniques of SO weakening,
see pages 453–454.
Some observations about
superior oblique weakening
1. Graded response. The response to superior
oblique tenotomy is graded one, i.e. the larger
overaction will show a greater response to the
same amount of surgery.
2. Effect on associated horizontal deviation. It
has been observed by several surgeons that
superior oblique tenotomy decreases the
exotropia and increases the esotropia as shown
in Table 11.1.
Since superior oblique tenotomy also influences the deviation in primary gaze; therefore,
by experience, the surgeons must make
adjustment for horizontal rectus muscle surgery
when being contemplated simultaneously.
Alternatively, the tenotomies may be performed
Table 11.1 Effect of superior oblique tenotomy on the
associated horizontal deviation
Procedure Decrease in exotropia or increase
in esotropia in prism dioptres
Upgaze Primary Down-
gaze gaze
Unilateral None 8–10 20–25
tenotomy
Bilateral tenotomy None 15 up to 70
first and the horizontal muscle surgery can be
taken later on. Of course, this will require two
general anaesthesias.
3. Effect on associated vertical deviation.
Secondary superior oblique overaction is almost
always associated with vertical deviation in
primary gaze and in its field of action. Superior
oblique tenotomy is expected to correct almost
full vertical deviation in the field of action of
the muscle and of up to 15 PD in the primary
gaze.
4. Tortional diplopia, a positive head-tilt test
and abnormal head posture have been reported
following bilateral superior oblique tenotomies
performed for secondary superior oblique
overaction in adults with a potential for single
binocular vision. However, such problems are
of no concern, if there is no potential for single
binocular vision.
DISSOCIATED STRABISMUS COMPLEX
Dissociated vertical deviation (DVD) is a
comparatively ill-understood form of strabismus.
That is why, it has been described under different
names by the different workers. A few of the
other names by which this condition has been
described are: Alternating sursumduction,
alternating hyperphoria, alternating hypertropia,
alternating sursumvergence, occlusion
hyperphoria, occlusion hypertropia, double
hypertropia, dissociated vertical divergence,
dissociated hyperdeviation and so on.
Dissociated vertical deviations are basically
characterized by a hyperdeviation in one eye
that is present while the other eye is fixing. The
non-fixing eye is also extorted and slightly
abducted. Thus, dissociated vertical deviation
(DVD) can be defined as an intermittent
anomaly of the non-fixing eye consisting of
upward excursion, excyclotorsion and lateral
deviation.
The term dissociated vertical deviation is
preferred because in it the two eyes are more
independent of each other (dissociated
movements) and do not follow the Hering's law
of ocular motility, i.e. in contrast to a true vertical
deviation, in DVD, the fellow eye does not
exhibit refixation movement in the opposite
direction.
278 Theory and Practice of Squint and Orthoptics
Since the upward drifting of the non-fixing
eye is often associated with lateral deviation and
excyclotorsion, the term ‘Dissociated
strabismus complex (DSC)’, has been suggested
to denote all the components, i.e. dissociated
vertical deviation (DVD), dissociated horizontal
deviation (DHD) and dissociated torsional
deviation (DTD).
DISSOCIATED VERTICAL DEVIATION
ETIOLOGY
Exact etiology of the DVD is not known.
Numerous theories have been put forward to
explain the occurrence of DVD. A few such
theories are mentioned below:
1. Bielschowsky's theory of positive and
negative subcortical vertical divergence centres.
Bielschowsky theorized that DVD occurs due to
alternating and intermittent excitation of both
subcortical vertical divergence centres.
However, this theory has not been further
substantiated.
2. Theory of imbalance of binocular stimulation.
Spielmann postulated that DVD is caused by an
imbalance of binocular stimulation. This theory
explains the frequent occurrence of DVD in
essential infantile esotropia and the occasional
occurrence with sensory heterotropia. However,
this theory does not explain the occurrence of
DVD in patients with otherwise normal
binocular functions.
3. Brodsky theory. According to this theory,
DVD is a vestigial remnant of the dorsal light
reflex of lower animals.
4. Other theories which have been put forward
include:
• Theory of bilateral paralysis of the depressor
muscles.
• Theory of defective mid-brain stimuli.
• Theory of two monocular conjugate mechan-
isms plus a binocular mechanism.
• Theory of defective monocular nasal retinal
quadrant stimuli.
• Guyton’s theory.
Thus many theories have been proposed to
explain occurrence of DVD. However, findings
of most of the theories could not be reproduced.
Therefore, the exact etiology is still illusive. The
lack of precise aetiologic information is further
reflected by the plethora of terms which have
been mentioned above to denote this condition.
CLINICAL FEATURES
1. Deviation. DVD is characterized by spontaneous occurrence of vertical deviation in either
eye, when the patient is fatigued, or day
dreaming (manifest DVD) or when fusion is
interrupted by artificial means (latent DVD)
(Fig. 11.4). Latent or phoric DVD (seen only
under cover) is more common than manifest or
tropic DVD. DVD is characterised by a slow
upward drifting of the non-fixing eye. The
vertically deviated eye is also extorted and
slightly abducted.
2. Associations of DVD: DVD may also occur
as an isolated phenomenon in patients with
apparently normal binocular function. In
general DVD may be associated with any congenital or acquired strabismus with motor fusion
deficiency. Its common associations include:
Infantile esotropia is associated with DVD in
over 75% cases. However, inspite of careful
search, the condition is rarely diagnosed in
infancy. It is usually diagnosed between 2 to 5
years of age. Mostly it becomes evident after the
surgical alignment for horizontal squint has
been done.
Infantile exotropia is also commonly associated
with DVD. It has been described to occur as a
part of a syndrome consisting of an A-pattern
exotropia with overaction of the superior
obliques and underaction of the inferior obliques
(Fig. 11.5).
Excycloduction and latent nystagmus are
frequently associated with DVD.
3. Head posture. Approximately, one-third of
patients with DVD have a spontaneous
abnormal head posture. Patient may adopt a
head tilt to the contralateral or ipsilateral side.
Head tilt may be adopted in order to control
latent nystagmus, minimize the amplitude of the
DVD or to establish peripheral fusion.
4. Laterality. DVD is frequently bilateral
(alternating sursumduction) usually asymmetric.
Rarely it may be monocular.
279Vertical Strabismus and Cyclodeviations
Fig. 11.4 Dissociated vertical deviation. (A) no initial
deviation; (B) left hypertropia with right eye fixing immediately
after removal of the cover from the left eye; (C) the left eye
is drifting down; (D) right hypertropia with left eye fixing
immediately after removal of the cover from the right eye;
(E) right eye is drifting back to its original position.
Fig. 11.5 Dissociated vertical deviation with associated
underaction of both inferior obliques (A and B) and overaction of both superior obliques (C and D).
Monocular dissociated hyperdeviation may be
seen in the presence of an intermittent exotropia.
It is frequently found that when fusion is broken
and the eye is deviated, the deviated eye
develops a small hyperdeviation. This deviation
is not associated with underaction of yoke
muscles and is not present, when the deviated
eye is not in abduction. It generally disappears
following horizontal surgical correction.
Bilateral DVD or alternating sursumduction is a
situation in which either eye elevates under cover
280 Theory and Practice of Squint and Orthoptics
(double hyperdeviation). Not only does elevation
takes place, but each eye tends to extort on
occlusion and slowly depress and intort, when
occlusion is removed. This deviation appears to
be related to retinal illumination. It is important
to note that in DVD when the hypertropic eye
fixates, there is no corresponding hypotropia of
the fellow eye (i.e. the eyes do not follow Hering's
law of equal innervation). While in hypertropia,
when the hypertropic eye fixates a target, the
other eye moves downwards into a hypotropic
position of equal magnitude.
Symmetric versus asymmetric DVD. Bilateral
DVD may be symmetric or asymmetric. Degree
of asymmetry of dissociated strabismus is
determined by the magnitude of the deviation
in primary position compared between the two
eyes.
5. Comitance. DVD may be comitant or
incomitant. The difference in the deviation of
non-fixing eye between the primary and in all
other gaze positions determines the degree of
incomitance.
Comitant DVD. DVD that measures roughly the
same (within 7 PD) in primary position,
adduction and abduction is called commitant
DVD. This is the most common presentation.
Incomitant DVD refers to measurable disparity
in the magnitude of DVD (>7 PD) between the
primary position, abduction, and adduction.
Incomitant DVD is usually associated with
muscle dysfunction as below:
1.DVD larger in the field of inferior oblique of the
non-fixing eye is characterized by following
features:
• In primary position, only DVD is seen.
• In adduction, both true hypertropia and DVD
are present.
• In abduction, DVD is <5 PD.
• ‘V’ pattern horizontal deviation may be
observed.
2.DVD larger in adducted position only, but DVD
in abduction is >5 PD.
3.DVD more in abduction due to associated
SOOA and ‘A’ pattern. As in the adducted
position, SOOA causes more depression than
the elevation occurring due to DVD so DVD
increases in the abducted position.
Superior rectus contracture syndrome in DVD.
Cases with marked asymmetric DVD, especially
those with reduced visual acuity in one eye, can
coexist with a superior rectus overaction/
contracture syndrome in the non-fixing eye. In
these cases, DVD is usually markedly decompensated and there occurs almost a permanent
elevated position of the non-fixing eye which
leads to shortening and contracture of the
superior rectus. The presence of a co-existing
superior rectus contracture syndrome in patients
with marked asymmetric DVD should be
suspected when the following clinical
characteristics are present:
• Hypertropia in the non-dominant eye in all
upgaze positions that is larger in supraabduction.
• Manifest hypertropia in the non-dominant eye
in primary position.
• Positive Beilschowsky head tilt test towards the
affected side.
• Hypertropia of the normal eye when the non-
dominant eye is fixing.
• Larger hypertropia when the non-dominant eye
is rotated down and out.
Note. Patients with superior rectus contracture
syndrome and DVD might need very large
recessions of the superior rectus (up to 14 mm).
It can be done in both eyes when symmetric DVD
is seen but mostly asymmetric SR recession is
required.
6. Binocular vision and sensory adaptations
• Suppression usually develops in patients with
spontaneous DVD and thus eliminates
diplopia.
• Peripheral fusion is often present in patients with
DVD having a manifest deviation of 4D or less.
• An absolute facultative central scotoma in one eye,
while both eyes are being used together for
peripheral vision, is present even in patients
having a latent DVD.
Hypotropic DVD
Hypotropic DVD is a rare condition. It is mostly
unilateral and commonly associated with
monocular visual deficits or high myopia.
Although the nature of this intermittent slow
downward ocular deviation is similar to that of
281Vertical Strabismus and Cyclodeviations
hypertropic DVD, it should be considered a
unique form of the dissociated strabismus
complex. The downward drifts are not
associated with any torsional movements and
no nystagmus is observed.
DIAGNOSIS
DVD is very often intermittent with great
variability in presentation posing formidable
challenges to proper diagnosis and
management. Repeated measurements are the
norm.
1. Cover-uncover test
• In patients with unilateral manifest DVD, when
the fixating eye is covered, there will occur a
downward movement of the uncovered eye
(but there will be no corresponding hypotropia
of the covered eye).
• In patients with alternate DVD, either eye
elevates under cover (double hyperdeviation)
while the uncovered eye will move down to
take fixation.
• In patients with latent DVD, there occurs no
movement of the uncovered eye, but the eye
under cover is elevated and moves downwards after it is uncovered (i.e. DVD is present
only when the eyes have been dissociated).
2. Spielmann’s translucent occluder test is better
than the simple cover-uncover test for DVD. In
a patient with latent DVD, through the
translucent occluder, the eyeball is seen to
upshift and there occurs characteristic slow
drifting recovery on removing the occluder
(Figs 11.6A and B). While in hypertropia
associated with inferior oblique overaction,
there occurs a refixation movement which is a
fast saccade.
3. Head tilt test. Most patients with DVD show
an increase in the size of DVD on contralateral
head tilt (e.g. DVD in right eye increases with
left head tilt). However, a few patients show
converse response.
4. Red glass (filter) test. Red glass (filter)
dissociates the two eyes and the eye behind the
filter drifts up in a patient with DVD and the
patient appreciates diplopia with red image
being lower. The fact that a patient will localize
the red image below the fixation light, regardless
of whether the red glass is held before the right
or left eye, clearly differentiates a DVD from
other forms of cyclovertical deviations in which
the red image is localized below or above the
fixation light, depending on which eye fixates.
5. Demonstration of Bielschowsky phenomenon.
In this test, one eye is covered with Spielmann
translucent occluder (and is elevated undercover)
while the other eye fixates (Fig. 11.6A). Then a
photometric graded density neutral filter bar is
placed before the fixing eye. In patients with DVD,
as the filter with gradually increasing density is
moved in front of the fixing eye, the elevated eye
under cover will start moving downwards
(Fig. 11.6C) and may go even below the primary
position. When the filter bar is moved from
positions of greater to lesser density the eye behind
the cover will again elevate (Fig. 11.6D). Since
Bielschowsky was first to note this intriguing
observation, hence it is known by his name.
6. Measurement of DVD
i. Prism base-down under the occluder test can be
useful in measuring DVD. In this test, prisms
with base-down are placed in front of the
deviating eye under the occluder and patient is
asked to focus on the fixation target at 6 m
distance. The occluder is then quickly shifted to
the fixating eye allowing the previously
dissociated and elevated eye to take up fixation.
The alternate cover test is continued and basedown prism is added until no downward
movement of the deviating eye is observed on
switching occlusion. In the case of bilateral DVD,
each eye is tested separately.
Grading of DVD, based on the degree, is as
below:
• 1+ DVD: A small deviation (up to 9 PD)
• 2+ DVD: A moderate deviation (10 to 19 PD)
• 3+ DVD: A large deviation ( >20 PD)
For a combined dissociated and a non-dissociated
vertical deviation, i.e. in patients with DVD and
true vertical deviation, measure the nondissociated component by adding base-up prism
over the non-DVD eye until the hypodeviation
is neutralized during the alternate cover test.
The next step is to measure the vertical deviation
as previously described for dissociated vertical
282 Theory and Practice of Squint and Orthoptics
Fig. 11.6 Detection of DVD using Spielmann's translucent occluder (A and B) and demonstration of Bielschowsky
phenomenon (A, C and D).
deviation. The actual dissociated vertical
deviation measured is the difference between
the two steps.
DIFFERENTIAL DIAGNOSIS
DVD must be differentiated from inferior
oblique overaction as shown in Table 11.2.
ii. Modified form of Krimsky test may be used to
measure DVD in patients who cannot fix with
deviating eye.
For grading the full deviation on cover test,
the occluder should be turned obliquely so that
the eye remains occluded and at the same time
examiner can look behind the occluder to grade
deviation (Fig. 11.7). Alternatively, a translucent
occluder may be used to disrupt fusion while at
the same time observing DVD undercover.
iii. An approximate grading of DVD may be done
on cover test as follows:
• 1 + DVD: A small deviation
• 2 + DVD: A moderate deviation
• 3 + DVD: A large deviation
TREATMENT
A. Non-surgical treatment is not so effective in
DVD. However, following measures may be
useful:
I. Conservative therapy to strengthen the
fusional mechanisms should be provided as
below:
• Optimal spectacle correction should be
prescribed. As the blurred vision may cause a
latent DVD to become a manifest more
frequently providing a clear images to both
eyes encourages fusion
• Correcting an associated horizontal deviation
either surgically or with prisms, promotes the
possibility of peripheral fusion.
Fig. 11.7 Technique of grading dissociated vertical
deviation on cover test using occluder in tilted positon.
• Treating amblyopia by occlusion therapy also
promotes peripheral fusion
• Treating heterophorias by orthoptics also
promotes peripheral fusion.
II. Conservative therapy in the form of changing
the fixation pattern by patching or optical
means may be useful, especially in patients with
asymmetric involvement or those accustomed
to wearing glasses. For example, if a patient is
having significant DVD of left eye while fixing
with right eye and an insignificant DVD of right
eye while fixing with left eye; a slight optical
blurr induced in the right eye by addition of
+2.0D lens will shift the fixation preference to
the left and DVD may no longer be a cosmetic
problem.
B. Surgical treatment It should also be borne in
mind that even the surgical treatment is also
palliative, since currently no such surgical
procedure is available that will completely cure
this disorder. Surgery is indicated, when DVD
causes a significant cosmetic problem, i.e.:
• When large DVD manifests frequently or
• Anomalous head posture in present to control
the DVD.
Note: Before contemplating surgery, it is
important to differentiate DVD from overaction
of the inferior oblique muscle (Table 11.2), since
the surgical approach to these two conditions is
different.
Following surgical procedures have been tried
by different workers:
283Vertical Strabismus and Cyclodeviations
Table 11.2 Dissociated vertical deviation versus inferior
oblique overaction
Sr. Feature Only Only
no. dissociated inferior oblique
vertical deviation over-action
1. Hyper- Present in Maximum in
deviation primary position adduction,
in adduction and never in
in abduction abduction
2. Incyclo- Present Absent
duction on
refixation
3. Speed of up- Slow Rapid
ward movement (2–200°/sec) (200–400°/sec)
in deviating
eye during
refixation
with nondeviating eye
4. Bielschowsky Present Absent
phenomenon
5. V-pattern Absent Present
6. Superior May Usually
oblique overact underaction
action
7. Pseudoparesis Absent Present
of contralateral
superior
rectus
8. Latent Often present Absent
nystagmus
9. External Absent Present
rotation of
fundus on
indirect
ophthalmoscopy (shown
by an altered
relation
between foveola and
optic disc)
I. Surgical procedures for comitant DVD
1. Faden operation with superior rectus
recession. In this procedure, a 3–5 mm recession
of the superior rectus muscle is combined with
anchoring this muscle to the globe with a nonabsorbable suture 12–15 mm posterior to its
insertion (posterior fixation suture, or
retroequatorial myopexy, or Faden operation).
This procedure is more effective than SR
recession alone, but recurrence occurring as late
284 Theory and Practice of Squint and Orthoptics
as several years after an initial satisfactory result
are reported by many workers. Botulinum toxin
A injection into SR has been suggested as an
alternative.
2. Large recession of superior rectus muscle.
Unconventionally, large recession (6 to 14 mm)
of superior rectus muscle has been suggested as
effective treatment for DVD. Bilateral recession
is indicated in bilateral cases of DVD. The
asymmetric amount of surgery may be
performed in the two eyes, when the deviation
is asymmetric. Graded recessions, recommended
based on the degree of DVD, are as below:
• Grade I (up to 9 PD): 5–7 mm
• Grade II (10–19 PD): 7–9 mm
• Grade III (>20 PD): 9–14 mm.
3. Resection of the inferior rectus muscle has also
been suggested by some workers. Preferably,
this procedure should be performed, if
recurrences occur even after the large recession
of superior rectus muscle. Recommended
amount of resection of the inferior rectus muscle
for DVD is 4 mm for small deviation, 6 mm for
intermediate deviation and 8 mm for large
angles. Resection of inferior rectus muscle may
also elevate the lower eyelid.
4. Recess-resect procedure. A 4–5 mm recession
of superior rectus muscle and 6 mm resection
of inferior rectus muscle have also been
recommended for treating large angle DVD.
However, this procedure should be limited to
those relatively infrequent patients who have a
predominantly monocular vertical deviation
with a hypertropia in primary position.
II. Surgical procedures for incomitant DVD
1. When DVD is larger (not more than 5 PD) in
the field of inferior oblique of the non-fixing eye,
i.e. in adducted position only, then the inferior
oblique weakening procedure, like IOAT is
preferred. As suggested by Scott, anterior
transposition of the inferior oblique muscle has
been an effective treatment for DVD with IOOA.
It is hypothesized that the IOAT procedure
creates a vector for depression, and this
antielevating force helps in controlling DVD.
This procedure can create a limitation of
elevation of the operated eye and may cause
hypotropia in primary position when performed
unilaterally.
It can also cause a restriction of elevation in
abduction associated with Y or V pattern when
performed bilaterally, particularly if the
posterolateral fibres of the inferior oblique
muscle are spread out laterally at the time of
resuturing to the sclera. This complication was
first called as ‘antielevation syndrome’ (AES) by
Kushner. IO transposition more than 1 mm
anterior to the inferior rectus muscle insertion
as well as lateral spreading of the posterior fibres
>2 mm at new insertion point are the risk factors
to develop AES.
2. When DVD is larger in adducted position but
significant in abduction (>5 PD) also. In these
patients, both SR recession and IO weakening
procedures are preferred.
3. When DVD is more in abduction due to
associated SOOA and ‘A’ pattern, following
procedures are required:
• Bilateral SR recession should be considered in
patients with small degree of A pattern (up to
12 PD).
• Additional SO weakening procedure like
posterior SO tenectomy is required with
bilateral SR recession in patients with larger
amounts of A-pattern (12–25 PD).
DISSOCIATED HORIZONTAL DEVIATION
Dissociated horizontal deviation (DHD) is
defined as a change in the horizontal ocular
alignment, unrelated to the accommodation,
that is brought about solely by a change in the
balance of visual input from the two eyes.
Characteristic features
• DHD usually manifests as spontaneous
unilateral exodeviation or an exodeviation of
greater magnitude in one eye during prism
and alternate cover testing.
• Unlike in other forms of intermittent
exotropia, the observed exodeviation is slow,
variable and asymmetrical in the two eyes.
• Sometimes may manifest as Eso-DHD.
Assessment
• To assess the horizontal dissociated deviation
(DHD), the same procedure as described for
DVD is performed with base-in prism over the
eye with DHD until no further inward
285Vertical Strabismus and Cyclodeviations
movement of that eye is seen. Movement of
the contralateral eye with this test can be
ignored.
• DHD may be distinguished from other horizontal
strabismus by lack of a corresponding
exodeviation of the contralateral eye on
alternate cover testing.
Treatment
• Exo-DHD, depending upon the amount, is
treated with LR recession of 3–8 mm on the
affected side.
• Exo-DHD, responds well to MR Recession
with or without Faden.
CYCLODEVIATIONS
Cyclodeviation (torsional strabismus) refers to
a misalignment of the eyes around the anteroposterior axes.
CLASSIFICATION
A. Depending upon the constancy of deviation
1. Cyclophoria
2. Cyclotropia
Theoretically, the cyclodeviations have been
classified into cyclophoria (latent cyclodeviation)
and cyclotropia (manifest cyclodeviation);
however, practically in most cases, no
distinction can be made between a cyclophoria
and a cyclotropia by means of the cover tests.
Therefore, practically the cyclodeviations cannot
be subdivided into latent and manifest forms.
B. Depending upon character of deviation
1. Excyclophoria and excyclotropia. The devia-
ted eye is extorted, i.e. the eye is rotated around
its anteroposterior axes in such a way that the
superior portion of the vertical meridian
(12 O'clock meridian) is torted temporally and
the inferior portion of the vertical meridian
(6 O'clock meridian) is torted nasally.
2. Incyclophoria and incyclotropia. The
deviated eye is intorted, i.e. the eye is rotated
around its anteroposterior axes in such a way
that the superior portion of the vertical meridian
(12 O'clock meridian) is torted nasally and the
inferior portion of the vertical meridian
(6 O'clock meridian) is torted temporally.
ETIOLOGY
In general, cyclodeviations result from an
imbalance in the relationship between intorters
(superior oblique and superior rectus) and
extorters (inferior oblique and inferior rectus)
of the eyeball under following situations:
1. Paresis or paralysis of any cyclovertical
muscle, particularly oblique muscles (having
larger torsional effect than vertical recti) is
commonly associated with cyclodeviation.
Cyclodeviation in such conditions is usually
associated with a vertical deviation, but may
also occur alone.
Bilateral excyclotropia secondary to closed head
injury occurs due to bilateral superior oblique
paralysis resulting from rupture of the anterior
medullary velum, which is that area in the
midbrain where the superior oblique fibres from
both superior oblique nuclei decussate.
2. Dissociated vertical deviations are frequently
associated with cyclodeviations.
3. A- and V-pattern of horizontal strabismus are
also associated with cyclodeviations without an
obvious paretic component.
4. Horizontal deviations and simple hyperphorias may also be associated with cyclodevi-
ations, though rarely.
5. Surgery on vertical recti or oblique muscles
may sometimes be complicated by cyclodeviations.
6. Uncorrected oblique astigmatism may also be
associated with cyclodeviation.
7. Other conditions which have been reported
to be associated with cyclodeviations include—
endocrine ophthalmopathy, myasthenia gravis
and plagiocephaly.
CLINICAL CHARACTERISTICS
Theoretically, one would expect that patients
with cyclodeviations should have symptoms
such as torsional diplopia, dizziness and
difficulties in negotiating stair way, steps and
street curves. However, in practice, most of the
patients are asymptomatic, with the exception
of paretic conditions of very recent onset,
particularly traumatic unilateral or bilateral
superior oblique paralysis. The reasons (factors)
which have been put forward for most of the
patients with cyclodeviations being asymptomatic are: