Vol.14
No. 1, Januray, 2004
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.
