The use of binocular visual acuity in the assessment of intermittent exotropia

Background: It has been suggested that a decrease in distance stereoacuity in patients with intermittent exotropia is a good indicator of diminishing control. However, there has been no adequate explanation for this reported reduction in distance stereoacuity in these patients. We postulate that the decrease in stereoacuity is related to blurred visual acuity created by an increasing demand on accommodation, which these patients use in an attempt to control the exodeviation, This can best be assessed by measuring binocu lar visual acuity (BVA). Analysis of BVA could provide a useful clinical to ol to evaluate control measures used by patients with intermittent exotropi a. Methods: A prospective study of patients with intermittent exotropia, ra nging in age from 6 to 60 years, was performed. Only those patients with th e presence of either basic or divergence excess (simulated or true) type ex odeviation were included in the study. The data analysis included the age o f these patients, age at onset of the deviation, monocular and binocular vi sual acuity, oculomotor and fusional status, and near and distance stereoac uity, Results: Data from 36 patients show that the measurements of BVA corr elated well with a corresponding loss of distance stereoacuity but not with the size of the deviation. Conclusion: The decrease of stereoacuity report ed in patients with exotropia can be explained by increased accommodation a nd decreased distance BVA. This measurement can be a simple method of quant ifying the fusional control of patients with intermittent exotropia.