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286 Theory and Practice of Squint and Orthoptics
• Cyclofusion
• Suppression and ARC
• Physiologic adaptation
• Psychologic adaptation
1. Cyclofusion. It has been reported that cyclo-
disparity caused by cyclodeviations is mostly
compensated by sensory cyclofusion which is
very well developed in humans. Normal
individuals can fuse up to 10°–15° of cyclodisparity
in either direction, by vertical and cyclofusional
movements. But only a few degrees of this
disparity are offset by motor fusion.
The effectivity of sensory cyclofusion is well
illustrated by comparing the testing of
cyclodeviation by two different methods as below:
When tested with Double Maddox rod test, a
patient shows cyclotropia. Same patients with
well-developed cyclofusion, when tested with
Bagolini lenses (after correcting the co-existing
vertical and horizontal deviations, if any, with
prisms), show that Maddox rod test which
disrupts fusion reveals the exact amount of
cyclotropia that can be measured exactly
whereas the Bagolini lenses which do not
disrupt fusion, test one's ability of cyclofusion.
2. Suppression and anomalous retinal correspondence. Some patients do not experience
torsional diplopia due to development of
suppression or anomalous retinal correspondence.
Note. It has been observed that even after
occlusion of the non-paralysed eye, the patient
does not see the visual environment tilted
inspite of the fact that the affected eye is rotated
around the anteroposterior axes. The cyclofusion
and suppression or ARC also cannot explain this
finding. Such a unique happening has been
explained by the occurrence of physiological
and psychological adaptation in patients with
cyclotropia. These phenomena are described
below.
3. Physiologic adaptation. It has been reported
that to compensate for the image tilt in some
patients with congenital or early acquired
cyclodeviation, there occurs a physiologic
adaptation in the form of spatial reorientation
of the horizontal and vertical retinal meridians
(Fig. 11.8). Perhaps such a physiologic adaptation
Fig. 11.8 Physiologic adaptation in the form of spatial
reorientation of the horizontal and vertical retinal meridia in
left eye with excyclodeviation. Note, image of a cross is no
longer formed on the normal vertical (V1–V2) and horizontal
(H1–H2) retinal meridia; but on the new vertical (Va1–Va2)
and new horizontal (Ha1–Ha2) meridia.
has a neurophysiologic basis in the form of a
change in orientation tuning of the striate
cortical neurons. Further, it has also been
reported that this physiologic adaptation is
reversible and after surgical treatment of
cyclotropia, patient may get normal orientation
after a brief period of seeing tilted environment.
4. Psychologic adaptation. A sort of psychologic
adaptation due to empirical spatial clues may
also help some patients with cyclotropia to be
unaware of the tilted environment. The
empirical spatial clues are based on the past
experience of seeing the orientation of the
familiar objects such as doors, windows, trees,
etc. in the physical space. This fact is supported
by the observation that patients with cyclotropia
(diagnosed on Maddox rod test) who do not see
287Vertical Strabismus and Cyclodeviations
the environment tilted may see a faintly
illuminated horizontal line as tilted, when no
other familiar visual clues are available.
DIAGNOSTIC TESTS
The deviated eye does not realign itself on
covering the fixating eye, its position remains
unchanged under monocular and binocular
conditions. Therefore, cyclodeviations cannot be
detected by routine objective examination.
Therefore, tests for their diagnosis are specially
done under following circumstances:
• When a patient complains of tilting of images
(which is not very often).
• When the examiner notices a torsional
movement of the eye on alternate cover test
(only a very experienced and observant
examiner can notice it).
• When there is a palsy of a vertical muscle,
especially one of the two obliques. Associated
vertical deviation is also noted.
• When it is detected while performing diplopia
fields with Franceschetti method.
Diagnostic tests for cyclodeviations can be
divided into subjective and objective tests.
Subjective diagnostic tests
The subjective tests can only be used for cyclo-
deviations beginning after visual maturation.
Subjective tests include the following:
• Maddox double rod test
• Maddox double prism test
• Maddox wing test
• Major amblyoscope test
• Bagolini's striated lenses test
• Lancaster red-green test
1. Maddox double rod test. Maddox double rod
test is a quantitative test to subjectively measure
the cyclodeviation; but it cannot differentiate
between cyclophoria and cyclotropia. It can be
performed at distance and near.
Procedure. To perform this test, patient is asked
to fixate a spotlight in a dark room. By means of
a trial frame, a white Maddox rod is placed
before the left eye, and a red Maddox rod before
the right eye with their axes set at 90°
(Fig. 11.9A). If no vertical deviation is present
(which is not very often the case), a 6 D prism is
placed with its base-down in front of one eye to
assist the patient in observing the two lines
easily (Fig. 11.9B). The results are interpreted
as below:
• If the two horizontal lines, one red and other
white, observed by the patient are parallel, no
cyclodeviation is present (Fig. 11.9C).
Fig. 11.9 Double Maddox rod test (for explanation, see text).
288 Theory and Practice of Squint and Orthoptics
• If the red line is tilted outward (Fig. 11.9D),
incyclodeviation is present and if the red line
is tilted inward (Fig.11.9E), excylodeviation is
present in the right eye. The examiner than
rotates the red Maddox rod inward or outward,
respectively until the red and white lines are
parallel. The amount of deviation is read in
degrees on the trial frame. For example, if the
red line which is tilted inward becomes parallel
at the 100° position, indicates that patient has
a 10° right excyclodeviation.
• Similarly, if cyclodeviation is present in left
eye the white line will be tilted depending
upon the type and degree of cyclodeviation.
• In the presence of bilateral cyclodeviation, e.g.
in bilateral excyclodeviation in a patient with
bilateral superior oblique palsy following
closed head injury both the white and red lines
will be tilted inward.
Note. It is important to note that with this test
cyclodeviated eye will always be the non-fixing
eye even when the patient fixes with the paretic
eye. For example, if a patient with a left superior
oblique palsy fixes with the left eye, the right
eye will show the excyclodeviation on the
double Maddox rod test, even though it is the
normal eye.
Drawback of the double Maddox rod test
Double Maddox rod test is of value in
substantiating and measuring cyclotropia since
it disrupts the fusion. But, as it does not permit
cyclofusion so it may be clinically insignificant
under casual viewing which allows cyclofusion.
The small frame size of the maddox rods,
available in most of the refraction trial boxes,
makes it difficult, if not impossible, to examine
for cyclodeviations in the peripheral field of
vision. The cyclophorometer designed by Burian
overcomes this problem but is not commercially
available.
2. Maddox double prism test. Maddox double
prism consists of two 4D prisms mounted base
to base in a frame. It displaces the image in
vertically opposite directions. To perform this
test, patient is asked to fixate on a horizontal
line drawn on a sheet of paper with the eye to
be tested (e.g. say right eye) and the double
prism is placed before the left eye. Patient sees
three lines, central with the right eye and upper
and lower with the left eye. The results of this
test are interpreted as below:
• No cyclodeviation is present, when all the three
lines are parallel.
• Right incyclodeviation is present, if the central
line is tilted outward.
• Right excyclodeviation is present, if the central
line is tilted inward.
Limitations
• This test can be performed only for near.
• Being a qualitative test, it cannot measure the
cyclodeviation and cannot differentiate
between cyclophoria and cyclotropia.
3. Bagolini's striated lenses test. Bagolini's
striated lenses permit testing for cyclotropia
under casual viewing conditions where
cyclofusion takes part. To perform this test,
patient is asked to fixate a spotlight in a dark
room. By means of a trial frame, the Bagolini's
striated lenses are placed before both eyes
with the axes of striations pointing towards
the 90° mark. These lenses will produce an
image of streak of light, perpendicular to the
axes of striations without obstructing the
surrounding fusible visual details (c.f.
Maddox rods). The results of this test are
interpreted as below:
• If the patient is able to fuse the two vertical
lines that indicate that cyclotropia is fully
compensated by cyclofusion.
• If the patient is unable to fuse the two vertical
lines, the lenses are turned until fusion occurs
and the amount and direction of the
cyclotropia is read on the trial frames.
4. Lancaster red green test. This is the most
complete test and has some advantages over
other tests:
• It measures the torsional amplitude of each
eye in nine different directions of gaze.
• It gives information about the pattern of
cyclodeviation in each direction of gaze, and
• Measures cyclodeviation simultaneously
along with the horizontal as well as vertical
deviations.
5. Synaptophore test is also very useful for
detecting and measuring the cyclodeviations.
289Vertical Strabismus and Cyclodeviations
Objective diagnostic tests
The objective diagnostic tests are useful for
revealing any cyclodeviation, regardless of the age
of onset (c.f. subjective tests). These tests include:
• Indirect ophthalmoscopy and fundus
photography.
• Monocular visual field charting
1. Ophthalmoscopy and fundus photography
Presence of cyclodeviation can be objectively
evidenced by a disturbed relationship of the
optic disc with foveola on indirect ophthalmoscopy and fundus photography. Normally,
the foveola is aligned approximately with the
junction of the middle and lower third of disc
(Fig.11.10A). In excyclodeviation, fundus is
rotated externally and the foveola appears to be
situated below a line extending horizontally
from just below the lower pole of optic disc
(Fig.11.10B). In incyclodeviation, fundus is
rotated internally and foveola appears to be
situated above a line extending horizontally
from the centre of the optic disc (Fig. 11.10C).
2. Monocular visual field testing. Evidence of
objective cyclodeviation can also be found on
monocular visual field charting which will show
inward rotation of the blind spot in excyclodeviation and outward rotation of the blind spot
in incyclodeviation.
Interpretation of results of objective and
subjective tests for cyclodeviation
1. Objective tests' results will always be positive
in the affected (cyclodeviated) eye.
2. Subjective tests' results are affected by various
factors such as cyclofusion, sensory adaptation,
physiologic adaptation and psychologic
adaptation. In patients with positive objective
tests for cyclodeviation, subjective tests may be
negative or reverse positive as follows:
i. Negative subjective tests. Subjective tests which
do not produce dissociation of fusion such as
Bagolini lenses test may be negative in patients
with positive objective tests for cyclodeviation.
It indicates complete compensation of deviation
by the cyclofusion.
ii. Reverse positive subjective tests. In contrast to that
observed on objective tests for cyclodeviation; on
the subjective tests, the cyclodeviated eye is
always the non-fixing eye. This is true even when
the non-fixing eye is normal and the opposite
fixing eye has a paretic cyclovertical muscle and
shows a cyclodeviation on objective tests. This
has been explained by the assumption that
perhaps a monocular sensorial adaptation takes
place in the paretic, fixing eye.
TREATMENT
Only symptomatic (subjective) cyclodeviation
(usually >5°) needs treatment, which is always
surgical. The choice of surgery is as follows:
1. Treatment of subjective cyclodeviation
associated with vertical deviation
i. When a patient gets hyperdeviation and
excyclodeviation due to unopposed action of the
inferior oblique following paralysis of
homolateral superior oblique muscle, obviously
the treatment is to weaken the offending inferior
oblique. This will correct both hyperdeviation
and excyclodeviation.
ii. When a patient develops vertical deviation
and cyclodeviation in the field of action of
paretic muscle (say superior oblique) without
Fig. 11.10 Fundus photograph showing relation of optic disc with foveola in a normal person (A), in a patient with
excyclodeviation (B) and, in a patient with incyclodeviation (C).
290 Theory and Practice of Squint and Orthoptics
any overaction of the antagonist (i.e. inferior
oblique); obviously the treatment of choice is
tucking of the tendon of paretic muscle (superior
oblique). Tucking of superior oblique will
eliminate both hyperdeviation and excyclodeviation occurring in its field of action.
iii.A patient having bilateral superior oblique
palsy producing V-pattern esotropia and an
excyclodeviation, needs bilateral tucking of the
superior oblique to fully correct the entill
problem.
2. Treatment of subjective cyclodeviation
without associated vertical deviation
Such a proposition is of rare occurrence but often
more difficult to handle; since a conventional
weakening or strengthening procedure on
cyclovertical muscle may correct the cyclodeviation but it may produce an unwanted
vertical deviation. Therefore, such surgical
procedures should be performed which will
exclusively affect the cyclodeviation. Following
procedures have been described:
i. Harada-Ito procedure (anterolateral advance-
ment of superior oblique tendon).
• This procedure, described in Japan, is becoming
quite popular for correction of monocular as
well as binocular excyclodeviation due to
palsy of superior oblique muscle.
• This procedure is based on the theoretical
assumption that only the anterior part of the
superior oblique tendon insertion is responsible
for incyclodeviation of eye.
• This procedure basically consists of anterolateral
advancement of the anterior part of the superior
oblique tendon. This will result in shift of the
line of pull in such a way that now on downgaze
intorsion occurs which overcomes the extorsion
without causing any vertical imbalance.
ii. Nasal transposition of inferior rectus muscle.
This procedure has been suggested as an
effective alternative for excyclodeviation in
downgaze, where Harda-Ito procedure is not
possible; for example, in patients with
congenital absence of superior oblique tendon
or in those where it has already been
tenotomized.
iii.Temporal transposition of the superior rectus
muscle may be added to nasal transposition of
inferior rectus muscle for correcting the
excyclotropia present in the primary position
(see Fig. 15.18).
iv. Temporal transposition of inferior rectus
along with nasal transposition of the superior
rectus muscle has been found effective for
correcting incyclodeviation.
v. Other procedures which have been reported
to correct cyclodeviation without producing
vertical or horizontal strabismus are:
• Slanting of the insertion of all rectus muscles.
• Vertical transposition of the horizontal rectus
muscles (see Fig. 15.19).
• Transposition of the anterior aspects of the
inferior and superior oblique tendons.
BIBLIOGRAPHY
1. Anderson, JR. Ocular vertical deviations and
nystagmus, London, 1959. British Medical
Association.
2. Bagolini, B, Campos, E, and Chiesi, C: Plagiocephaly causing superior oblique deficiency and
ocular torticollis, Arch. Ophthalmol. 100:1093, 1982.
3. Bielschowsky, A: Die einseitigen und
gegensinnigen ("dissoziierten") Vertikalbewegungen der Augen, Graefes Arch. Ophthalmol.
125:493, 1931.
4. Bielschowsky, A: Lectures on motor anomalies.
Hanover NH, 1956, Dartmouth Publishing Co.
5. Burke, JP, Scott, WE, and Kutschke, PJ: Anterior
transposition of the inferior oblique muscle for
dissociated vertical deviation. Ophthalmology
100:245, 1993.
6. Duncan, L, and Noorden, GK von: Surgical
results in dissociated vertical deviations, J
Pediatr. Ophthalmol. Strabismus 21:25, 1984.
7. Esswein. MB, Noorden, GK von, and Coburn,
A. Comparison of surgical methods in the
treatment of dissociated vertical deviation, Am
J Ophthalmol. 113:287, 1992.
8. Fink, WH, Surgery of the vertical muscles of
the eye, ed. 2, Springfield, III., 1962, Charles C
Thomas, Publisher, P. 369.
9. Guyton, DL and Noorden, GK von: Sensory
adaptations to cyclodeviations. In Reinecke.
RD, editor: Strabismus, New York, 1978, Grune
& Stratton, Inc.
10. Harada, M and Ito, Y: Surgical correction of
cyclotropia, Jpn J Ophthalmol. 8:88, 1964.
11. Helveston, EM: Dissociated vertical deviaton: a
clinical and laboratory study, Trans. Am
Ophthalmol. Soc 78:734, 1980.
291Vertical Strabismus and Cyclodeviations
12. Herzau, V and Joos-Kratsch, E: Objective and
subjective evaluation of xyclovergence and
cyclofusion, Doc. Ophthalmol. 58:85, 1984.
13. Hooten, K, Myers E, Worall, R, and Stark, L:
Cyclovergence: the motor response to
cyclodisparity, Graefes Arch. Ophthalmol.
210:65, 1979.
14. Kii, T, Ogasawara, K, Ohba, M, Hotsubo, M,
Sakai, N and Nakagawa, T: The effectiveness of
the Faden operation on the superior rectus
muscle combined with recession of the muscle
for the treatment of dissociated vertical
deviation, Acta Soc. Opthalmol. Jpn. 98:98,
1994.
15. Mumma, JV: Surgical procedure for congenital
absence of the superior oblique, Arch.
Ophthalmol. 92:221, 1974.
16. Noorden, GK von, Brown, DJ, and Parks,M:
Clinical observations in cyclotropia. Presented
at the American Orthoptic Council - American
Association of Certified Orthoptists symposium
at the American Academy of Ophthalmology
and Otolaryngology, Dallas, September 16, 1973.
17. Noorden, GK von: Clinical observations in
cyclodeviations, Ophthalmology 86:1451, 1979.
18. Noorden, GK von: Indications of the posterior
fixation operation in strabismus, Ophthalmology
85:512, 1978.
19. Noorden, GK von, and Chu, MW: Surgical
treatment options in cyclotropia, J Pediatr
Opthalmol Strabismus 27:291, 1990.
20. Ogle, KN, and Ellerbrock, VJ: Cyclofusional
movement, Arch. Ophthalmol 36:700, 1946.
21. Oliver, P, and Noorden, GK von: Excyclotropia of
the nonparetic eye in unilateral superior oblique
muscle paralysis, Am J Ophthalmol. 93:30, 1982.
22. Ruttum, M, and Nooden, GK von: Adaptation to
tilting of the visual environment in cyclotropia,
Am J Ophthalmol 96:229, 1983.
23. Spielmann, A: A translucent occluder for
studying eye position under unilateral or
bilateral cover test, Am. Orthopt J 36:65, 1986.
24. Spielmann, A: Les divergences verticales
dissociees: exces de sursumversion lie a la
fixation, Ophthalmologie 1:457, 1987.
25. Spielmann, A: The oblique Kestenbaum
procedure revisited (sloped recession of the recti).
In Lenk-Schafer, M, editor: Orthoptic horizons,
Transactions of the Sixth International Orthoptic
Congress, Harrogate, England, 1987, p. 433.
292 Theory and Practice of Squint and Orthoptics
12
Incomitant Strabismus
CLASSIFICATION
VERTICALLY INCOMITANT HORIZONTAL
HETEROTROPIAS
(A-, V-, X-, Y- and -PATTERN HETEROTROPIAS)
Terminology
•
Etiology
•
Clinical characteristics
•
Treatment
•
PARALYTIC SQUINT
Etiology
Clinical features
Investigations
Differential diagnosis
Clinical varieties of ocular palsies
Isolated ocular muscle paralysis
•
Paralysis of 3rd cranial nerve
•
External ophthalmoplegia
•
Total ophthalmoplegia
•
Internuclear ophthalmoplegia
•
CLASSIFICATION
Incomitant squint is a type of heterotropia
(manifest squint) in which the amount of
deviation varies in different directions of gaze.
Further, amount of deviation may also vary
depending on which eye is fixing. Incomitant
deviations include the following conditions:
1. Vertically incomitant horizontal heterotropias
(A-, V-, X-, Y- and -pattern heterotropias)
2. Paralytic strabismus
i. Paralytic esotropia
• Lateral rectus paresis or paralysis
• Divergence paralysis
RESTRICTIVE OCULAR MOTILITY DEFECTS
Restrictive strabismus due to misdirected muscle
forces
Congenital cranial dysinnervation disorders (CCDDs)
CCDDs primarily affecting horizontal ocular motility
•
CCDDs primarily affecting vertical ocular motility
•
CCDDs primarily affecting facial muscles with
•
associated ocular motility defects
Restrictive strabismus due to mechanical restriction
Tight extaocular muscles
Brown’s syndrome.
•
Thyroid ophthalmopathy
•
Orbital blowout fracture
•
Strabismus fixus
•
Congenital tight inferior rectus muscle
•
Structural adhesions
Adherence syndrome
•
Tight lateral rectus syndrome
•
Contracture of extraocular muscles
•
Adhesive syndrome
•
Postoperative scarring
•
Orbital myositis
•
ii. Paralytic exotropia
• Isolated medial rectus paresis
• Complete third nerve paralysis
• Paralysis of convergence
iii. Paralytic vertical deviation
• Single muscle paresis or paralysis
– Superior oblique paralysis or paresis
– Inferior oblique paralysis or paresis
– Superior rectus paralysis or paresis
– Inferior rectus paralysis or paresis
• Part of complete third nerve paralysis
• Supranuclear lesions
Incomitant Strabismus
293
– Double elevator paralysis
– Double depressor paralysis
3. Restrictive ocular motility defects
A. Restrictive strabismus due to misdirected muscle
forces
1. Congenital cranial dysinnervation disorders
(CCDDs)
2. Congenital ectopic extraocular muscle
insertion and/or pulley location
3. Displaced extraocular muscle
B. Restrictive strabismus due to mechanical
restrictions
1. Tight extaocular muscles
• Inelastic superior oblique in congenital
Brown’s syndrome
• Thyroid ophthalmopathy
• Entraped inferior rectus muscle in blow-
out fracture of orbital floor
• Monocular elevation deficiency (MED),
caused by fibrotic IR muscle
• Strabismus fixus
2. Structural adhesions
• Fat adherence to extraocular muscles or
sclera after strabismus surgery, retinal
detachment surgery or periocular trauma
• Congenital fibrotic bands
• Acquired Brown’s syndrome due to
scarring/inflammation around, the trochlea
• Conjunctival and Tenon’s capsule scarring
3. Orbital mass lesions
• Orbital tumours causing mass effect on
the globe movements
• Glaucoma explant with large bleb causing
mass effect.
A-pattern and V-pattern which are now
accepted worldwide. In practice, the term
vertically incomitant horizontal heterotropias
has become synonymous with "A- and Vpattern". A few other patterns are also recognized
as follows.
A-pattern horizontal heterotropia
An A-pattern designates a vertically incomitant
horizontal heterotropia with increasing convergence (decreasing divergence) in upgaze and
increasing divergence in downgaze. An A-pattern deviation is considered clinically significant,
when the difference between upgaze and
downgaze is at least 10 prism dioptres or more.
• A-esotropia: Esotropia will increase in
upgaze and decrease in downgaze (Fig. 12.1).
• A-exotropia: Exotropia will decrease in
upgaze and increase in downgaze (Fig. 12.2).
Fig. 12.1 A-pattern esotropia. Note left esotropia in primary
gaze (A) which increases in upgaze (B) and decreases in
downgaze (C).
VERTICALLY INCOMITANT HORIZONTAL
HETEROTROPIAS (A-, V-, X-,Y- AND
-
PATTERN HETEROTROPIAS)
TERMINOLOGY
The term vertically incomitant horizontal
heterotropias refers to those horizontal
deviations that change in magnitude with
upgaze and downgaze. Urist introduced this
concept to American literature in 1951 and
Albert suggested the excellent descriptive terms
Fig. 12.2 A-pattern exotropia. Note left exotropia in primary
gaze (A) which decreases in upgaze (B) and increases in
downgaze (C).
294 Theory and Practice of Squint and Orthoptics
V-pattern horizontal heterotropia
The V-pattern is present, when there is vertically
incomitant horizontal deviation with increasing
convergence (decreasing divergence) in
downgaze and increasing divergence in upgaze.
The V-pattern is considered clinically significant,
only when it measures 15 prism dioptres or more
difference between upgaze and downgaze.
• V-esotropia. The esotropia will increase in
downgaze and decrease in upgaze (Fig. 12.3).
• V-exotropia. The exotropia will increase in
upgaze and decrease in downgaze (Fig. 12.4).
Y-pattern horizontal heterotropia
Patients with Y-pattern have exotropia only in
upgaze (Fig. 12.5).
(lambda)-pattern horizontal heterotropia
These patients have exotropia in downgaze
only.
Fig. 12.3 V-pattern esotropia. Note left esotropia (A) which
decreases in upgaze (B) and increases in downgaze (C).
Fig. 12.5 Y-pattern exotropia. Note left exotropia in upgaze
(A) and no deviation in primary gaze (B) and downgaze (C).
X-pattern horizontal heterotropia
These patients essentially have no deviation or
only a small one in primary position, but a
significant exotropia is present in upgaze as well
as in downgaze (Fig. 12.6).
ETIOLOGY
Various theories have been put forward to
explain the occurrence of A- and V-patterns.
However, it has not been possible to explain the
occurrence of such patterns in every case by any
single aetiological factor. Perhaps different
factors might be responsible in different cases.
Each of the following conditions has been firmly
documented as a cause of A- and V-patterns:
Fig. 12.4 V-pattern exotropia: Diagrammatic depiction of left
exotropia (A) which increases in upgaze (B) and decreases in
downgaze (C).
Fig. 12.6: X-pattern exotropia. Note no deviation in primary
gaze (A) and exotropia in upgaze (B) and downgaze (C).
Incomitant Strabismus
295
1. Oblique muscle dysfunction. Dysfunction of the
oblique muscles is the most common clinical
finding and surgery on these muscles has been
eminently successful in the elimination of these
patterns. Following observations have been made:
• Inferior oblique overaction is frequently
associated with V-patterns and surgical
weakening of this muscle is effective in
correcting the anomaly in most of such cases.
• Superior oblique overaction is often associated
with A-patterns and surgical weakening of
these muscles is effective in correcting the
anomaly in majority of such patients.
Factors blamed for oblique muscle dysfunction are
as follows:
• Innervational (primary or secondary
overaction).
• Desagittalization of the muscle planes, i.e.
disturbed parallelism of the superior and
inferior oblique muscles.
• Anomalous insertion of oblique muscles.
• Ocular or orbital torsions.
The cause of oblique muscle dysfunction
seems to be of secondary importance with
regard to the management of these conditions.
The main point is to search for the overacting or
underacting oblique muscles. Unfortunately,
there are some cases of A- and V-patterns that
clearly do not show overaction of the obliques;
and an alternative explanation and surgical
treatment for these patients is necessary.
2. Horizontal rectus muscle dysfunction. Urist
(1958) hypothesized that horizontal recti are
responsible for A- and V-patterns as follows:
• A-esotropia: Underacting lateral recti.
• A-exotropia: Underacting medial recti.
• V-esotropia: Overacting medial recti.
• V-exotropia: Overacting lateral recti.
But, no convincing evidence has been
presented to explain A- and V-patterns
exclusively on a dysfunction of the horizontal
recti.
However, surgically supraplacement and
infraplacement of the medial and lateral recti
are effective procedures for A-V-pattern, when
not associated with overaction of the obliques.
3. Vertical rectus muscle dysfunction. Brown
(1953) suggested that A-V-patterns may be
caused by vertical rectus muscle dysfunction.
However, this concept never gained popularity
due to lack of any supporting evidence. Further,
the horizontal transposition of the vertical recti
proposed to correct A-V-pattern had also not
been found very effective and thus not used
today.
4. Orbital factors. It has been proposed that an
apparent dysfunction of the oblique muscles
unrelated to paresis of any cyclovertical muscle
might be due to some structural orbital anomalies
as evidenced by following observations of
several workers:
• Patients with Alpert's syndrome or Crauzon's
syndrome frequently show a V-pattern
exotropia or esotropia with marked elevation
of the adducting eye, which resemble the
pattern caused by overacting inferior obliques.
• Patients with upward or downward slanting
palpebral fissures may show A- and V-patterns.
• Orbital factors might be responsible for
desagittalization of the muscle planes which
in turn might be producing A- and V-patterns
in some cases.
5. Pulley abnormalities in the form of heterotopia
or laxity of the pulley have also been reported
as a cause of ‘A’ and ‘V’ patterns. Diagnosis of
pulley abnormalities is made on MRI orbital
imaging. In such cases, surgery could be
performed to stabilize or reposition the orbital
pulley.
CLINICAL CHARACTERISTICS
Prevalence
Exact prevalence varies depending upon the
criteria used to define the condition, degree of
upgaze and downgaze used to test and the ethnic
group tested. However, in general, between 15%
and 50% of all strabismus cases have been
reported to have associated A- or V-pattern in
different studies. Common patterns found in
clinical practice are V-esotropia, V-exotropia, Aesotropia and A-exotropia.
Symptoms and signs
Since fusion may have to be maintained for a long
time in certain positions of gaze, so patients with