Effect of Occlusion Therapy on Angle
of Strabismus in Patients of
Strabismic Amblyopia
Supratik Bandyopadhyay, Amod
Gupta
INTRODUCTION
Development amblyopia is defined as
decrease in visual acuity in one or
both eyes that results from an
inability to use the eye or eyes for
central fixation during critical
period of visual development. In
human this critical period ranges
from birth to approximately 6 years
of age. Strabismus accounts for 33%
to 45% cases of amblyopia.1
Strabismic patients are 14.7 times
more prone to become amblyopic than
non-strabismic individuals.2
In the treatment of amblyopia one of
the considerations is the
possibility of the angle of
deviation being influenced by
occlusion therapy. However, this
aspect of occlusion therapy has
drawn little attention. Some
observers have noted a change in the
angle of esotropia after occlusion
therapy for convergent strabismic
amblyopia.3 The purpose
of this study was to find out the
effect of conventional full-time
occlusion therapy on angle of
deviation in strabismic amblyopia.
MATERIAL AND METHODS
This study included 51 patients
of strabismic amblyopia. Patients
who had combined strabismic and
anisometropic amblyopia were also
included in the study. A difference
of 2 lines or more on a visual
acuity chart was used as diagnostic
criterion for amblyopia. A
difference between the spherical
equivalents of the eyes exceeding
1.50 diopter was considered
anisometropia. Strabismic amblyopes
who had constant esotropia or
exotropia were the subjects for this
study. The patients who had
intermittent esotropia or
intermittent exotropia were not
included in the study.
Criteria
for inclusion:
1.
The children aged between 4 and 10
years at the time of initiation of
occlusion therapy.
2. On
motility examination a manifest
esodeviation or exodeviation was
present at near and distant fixation
after full correction of refractive
errors with a spherical equivalent
of more than 2.00 diopters at least
for 2 weeks.
3.
The patients who had not been
treated with occlusion before and
had not undergone previous eye
muscle surgery.
4. No
change in refraction or glasses had
occurred during the period of
occlusion therapy.
All
patients underwent complete
ophthalmologic and orthoptic work up
prior to treatment. A cycloplegic
refraction was carried out using
atropine 1% or cyclopentolate 1% at
the first visit. best corrected
visual acuity was recorded, using
illiterate 'E' Chart or Snellen
Chart after full correction of
refractive errors with a spherical
equivalent of more than 2.00
diopters. The amount of strabismus
at near fixation (33 cms) and
distant fixation (6 meters) was
measured by prism cover test (PCT)
after refractive correction had been
worn for at least 2 weeks prior to
occlusion therapy. The measurement
of deviation by Krimsky test was
done when prism cover test was not
possible either because of severely
decreased visual acuity or
uncooperative patients who were
unable to fix at a distant target.
All patients underwent full-time
occlusion of the better eye using
adhesive eye patch for all working
hours.
In
patients aged 4-6 years, 6 days of
full-time occlusion of the better
eye was followed by one day of
occlusion of the affected eye. But
patients older than 6 years
underwent full-time occlusion of the
better eye without any inverse
occlusion (occlusion of the affected
eye). In addition patients were
advised to do near visual tasks.
The patients were followed up at
monthly interval for three months
after initiation of occlusion
therapy. In teach follow up visit
the distant visual acuity was
recorded using the same visual
acuity chart that was used at the
time of starting occlusion
treatment. The angle of strabismus
and fixation preference were
recorded by the same examiner using
same method at each follow up visit.
RESULTS
Twenty eight of the 51 patients
(54.9%) were male and twenty three
(45.1%) were female. Age of the
patients ranged from four years to
ten years (Average 5.8 years). The
initial mean angle of deviation
measured by prism cover test in 22
out of the 51 patients was 37.05
prism diopters for near and 31.9
prism diopters for distance. The
mean angle of deviation measured by
krimsky test in the remaining 29
patients was 29.5 prism diopters for
near fixation. The mean angle of
deviation measured by prism cover
test in 17 out of 42 patients with
convergent strabismic amblyopia was
38.3 prism diopters for near and
33.6 prism diopters for distance,
where as the mean angle of deviation
measured by krimsky test in the
remaining 25 patients with
convergent strabismic amblyopia was
35.2 diopters. The mean angle of
deviation measured by prism cover
test in 5 of the 9 patients with
divergent squint was 35.0 prism
diopters for near and 25.6 prism
diopters for distance where as the
mean angle of deviation measured by
krimsky test in the remaining 4
patients was 29.5 prism diopters for
near.
In
patients with deviation measured by
prism cover test, the angle of
deviation increased in 32% and
decreased in 54% of the patients for
near fixation, whereas it increased
in 9% and decreased 54% of the
patients for distance fixation. In
patients with deviation measured by
krimsky test, the angle of deviation
increased in 10% and decreased in
41% of the patients. There was a
mean decrease of 2.6 prism diopters
in deviation for near as well as for
distance as measured by prism cover
test at 3 months follow up and this
decrease in mean deviation was not
statistically significant (p>0.1).
Following occlusion either an
increase or a decrease of 5 prism
diopters or more in the angle of
deviation on prism cover test
occurred in 53% of the patients at
near fixation and in 35% of the
patients at distance fixation. In
patients with deviation measured by
krimsky test, a change of 5 prism
diopters or more in the angle of
deviation occurred in 36% of the
patients.
DISCUSSION
Full-time occlusion of the normal
eye has been the most widely used
modality of treatment for amblyopia
and can improve the visual acuity to
6/12 or better in 88% of the
patients of amblyopia with macular
fixation. Some observers 3,4
reported changes in the angle of
esotropia following occlusion
therapy for amblyopia but the
observations have been dissimilar.
Swan4 noted a
significant increase in the angle of
esotropia in 4.0% of his patients
following occlusion therapy. In our
patients with convergent strabismic
amblyopia an increase or decrease of
five prism diopters or more in
deviation occured in 53% of the
patients at near fixation and 35%
of the patients at distance fixation
when the deviation was measured with
prism cover test and in 36% patients
when the deviation was measured with
krimsky test. In our patients with
divergent strabismic amblyopia, none
of the nine patients had an increase
in deviation and four patient had a
decrease of five prism diopters or
more in deviation. As the number of
patients was too small, no definite
conclusion could be drawn regarding
the effect of occlusion on exotropia.
Some observers reported that
patients with mild amblyopia (visual
acuity between 20/40 and 20/70 )
were more likely to increase or
decrease their angle of deviation
with occlusion therapy. We, however,
didn't study this aspect.
CONCLUSIONS
All these observations indicate that
variations in the angle of squint do
occur following occlusion treatment
for amblyopia but these are not
always in the direction of increased
deviation. Moreover there is an
increased chance of decrease in the
angle of deviation following
occlusion therapy for strabismic
amblyopia.
REFERENCES
-
Shaw
DE, Minshull G, Fielder AR,
Rosenthal AR. Amblyopia
Factors influencing age of
presentation. lancet 1988;
23:207-209.
-
Abrahamson M, Fabian G,
Sjostrand J. Refraction Changes
in Children developing
convergent or divergent squint.
Br. J Ophthalmol 1992: 76:
723-727.
-
Pine
L, Shippman S. The influence of
occlusion therapy on
esodeviation. Am Orthopt. J
1982; 32:61-65.
-
Swan
KG. Esotropia following
occlusion. Arch Ophthalmol
1947; 37: 444-451.
Address for Correspondence
Dr. Supratik Bandyopadhyay,
Deptt. of Ophthalmology, PGIMER,
Chandigarh
