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 binocular visual acuity (BVA). Analysis of BVA could provide a useful clinical tool to evaluate control measures used by patients with intermittent exotropia. METHODS: A prospective study of patients with intermittent exotropia, ranging in age from 6 to 60 years, was performed. Only those patients with the presence of either basic or divergence excess (simulated or true) type exodeviation were included in the study. The data analysis included the age of these patients, age at onset of the deviation, monocular and binocular visual acuity, oculomotor and fusional status, and near and distance stereoacuity. RESULTS: Data from 36 patients show that the measurements of BVA correlated well with a corresponding loss of distance stereoacuity but not with the size of the deviation. CONCLUSION: The decrease of stereoacuity reported in patients with exotropia can be explained by increased accommodation and decreased distance BVA. This measurement can be a simple method of quantifying the fusional control of patients with intermittent exotropia.