Evaluation of factors influencing distance stereoacuity on Frisby-Davis Distance Test (FD2) in intermittent exotropia

Abstract

Aim: To evaluate the factors affecting the restoration of stereoacuity after surgery in cases of intermittent exotropia.

Methods: Thirty consecutive patients of intermittent exotropia X (T) scheduled for surgical intervention underwent preoperative evaluation, including complete ophthalmic and orthoptic examination. Deviation was measured for near and distance. Near stereo acuity was measured by The Netherland Organization stereotest (TNO), and distance stereo acuity was measured using the Frisby-Davis Distance (FD2) stereotest at 6 m for all cases and age-matched controls. All cases of X (T) were followed postoperatively at 1 week, 1 month, 3 months and 6 months.

Results: Successful surgical alignment, defined as alignment within eight prism dioptres of exophoria, was seen in 84% of cases. The median distance stereo acuity improved from preoperative value of 50 s of arc to 17.5 s of arc, and near stereoacuity improved from 240 s of arc to 90 s of arc at 6 months postoperatively. The median distance and near stereo acuity in controls were 15 and 60 s of arc respectively. There was a significant difference in both distance and near stereoacuity between controls and cases, even after surgery. A high grade of preoperative stereoacuity was found to be a significant factor in determining the achievement of normal stereoacuity postoperatively. Age and amount of pre- and postoperative deviation were not found to have any affect. None of the above-mentioned factors had any influence on successful postoperative surgical correction.

Conclusion: There is a significant improvement in both near and distant stereoacuity postoperatively in X (T); however, the achievement of normal level depends upon the preoperative sensory status of the patient.