Vol.13  No. 1,  October 2003

CORRELATION BETWEEN CHANGE IN FIXATION GRADE AND IMPROVEMENT IN VISUAL ACUITY FOLLOWING OCCLUSION THERAPY FOR STRABISMIC AMBLYOPIA.

Dr. Supratik Bandyopadhyay , Dr. Moheep Singh, Dr. Amod Gupta

INTRODUCTION

Amblyopia is defined as decrease in visual acuity in one or both eyes caused by inability to use the eye or eyes for central fixation during critical period of visual development.  In human this period ranges from between birth to 6 years of age.  Among different causes of amblyopia strabismus is the most common one and esotropia is more commonly associated with amblyopia than exotropia.1  Among different treatment modalities available conclusion of the non-amblyopia assessment of visual acuity is difficult in younger children.  Assessment of the fixation behaviour  of an amblyopic eye gives an approximate idea about the visual acuity in  that eye2.  An improvement in the fixation pattern is considered to be an indirect evidence of improvement in the visual acuity of the amblyopic eye.3  The present study was conducted to find out the correlation between improvement in distant visual acuity and change in fixation grade following occlusion therapy for strabismic amblyopia.

Materials and Methods

This was a prospective study conducted in a tertiary eye care centre in northern India.  The study included 51 eyes of 51 patients of strabismic amblyopia.  The patients, whose age were between 4 to 10 years were included in the study.  The patients who had a combination of anisometropic and strabismic amblyopia were also included in the study. Amblyopia was defined as difference of one line or more in  Snellen visual acuity in two eyes.  Anisometropia was considered when there was 1.5 diopter or more difference in the refractive error in two eyes.  All patients underwent cycloplegic refraction under atropine ointment 1% used twice daily for three days.  Visual acuity was assessed after full refractive correction had been worn for atleast two weeks.  Visual acuity was assessed by Snellen's chart in older children and with illiterate 'E' chart in a younger individuals.  Fixation pattern was graded as described by Dale.4  Visual acuity and grade of fixation was assessed at the initiation occlusion therapy.  All patients were given occlusion of the dominant eye for all waking hours.  The schedule of occlusion was modified according to the age as prescribed by Dale. 4  Patients were followed up at monthly intervals for 6 months.  At each follow up visit visual acuity and fixation grade was assessed using same set up and method.

Results

28 of 51 (54.9%) were male patients and mean age was  5.8 years.  The mean log mar visual acuity at presentation was 0.81 ( equivalent to 6/36) at 3 months follow up was improved to 0.45.  Fixation grade at presentation varied from 5 to 10 with average of 3.13 which at 3 months improved to 2.4 which was statistically significant.  41 patients (80%) had one line or more improvement in distance visual acuity whereas only 17(33%) patients had improvement in fixation (grade out of 17 patients where there was improvement in fixation grade 14 patients (82%) also had simultaneous improvement in Snellen's visual acuity and in only 3 patients (18%) fixation improved without accompanying improvement in visual acuity.

DISCUSSION

Full time occlusion of the normal eye has been the most widely used modality to treatment for amblyopia and can improve the visual acuity to 6/12 or better in 88% of amblyopic patients with monocular fixation.  We observed an improvement in distant visual acuity in 80% of patients but at the same time we had patients with eccentric fixation.   The assessment of fixation preference has good sensitivity for diagnosing amblyopia of 3 lines or more in patients with deviations greater than 10 prism diopters where as small angle tropias have a high false positional rate with 40% of now amblyopic patients responding with strong fixation preference.  After occlusion for amblyopia a change in fixation preference is usually accompanied by an improvement in the visual acuity.  In the present study 82% of patients with improved fixation grade also had improvement in visual acuity whereas 79% of patients with no improvements in fixation grade also had improvement in visual acuity.

CONCLUSION

There is no statistically significant correlation between improvement in visual acuity and change in fixation grade.  But during occlusion if one shows improvement in fixation grade it is a strong indicator of accompanying improvement in visual acuity.

REFERENCES

  1. Oliver M , Nawartzki I. Screening of pre-school children for ocular anomalies (II) Amblyopia Prevalance and therapeutic results at different ages.  Br J Ophthalmol 1971; 55: 467-471.

  2. Harley Robinson D. Pediatric Ophthalmology 2nd ed  W B  Saunders 1983; 338-339.

  3. Lazich B M.  Amblyopia exanopsia.  Arch Ophthalmol 1948; 39; 183-185.

  4. Dale RT. Fundamentals of ocular motility and strabismus.  Grune and Stratton 1982.

  5. Catford GV. Amblyopic occlusion: The results of treatment.  Trans Ophthalmol Soc UK 1967; 87: 179-193.

  6. Abrahmson M, Fabian G, Sjostrand J. Refraction changes in children developing convergent or divergent Squint.  Br J Ophthalmol 1992; 761: 723-727.

  7. Brich EE,  Stager DR. Prospective assessment of acuity and stereopsis in amblyopic infantile esotropes following early surgery.  Invest Ophthalmol Vis Sci 1990; 758-765.

Department of Ophthalmology, 
Post Graduate Institute of Medical Education and  Research, Chandigarh

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