The Ratio of Accommodative-Convergence to Accommodation in Patients with Intermittent Exotropia

ABSTRACT

PURPOSE: To measure the ratio of accommodative-convergence to accommodation (AC/A ratio) in patients with pseudodivergence excess type and convergence insufficiency type of intermittent exotropia [X(T)], and to compare with a normal group. METHODS: A total of 55 subjects were divided into 3 groups pseudodivergence excess type, convergence insufficiency type, and normal group. Age, gender, and refractive error of patients were examined. The deviation angle was measured at near and distance by using a prism cover test, followed by an interpupillary distance measurement. The AC/A ratio was calculated using a heterophoria and a gradient method. RESULTS: There was no statistically significant difference in age, gender, and the refractive errors among the 3 groups. The mean value of AC/A ratio using the heterophoria method was 9.50 in pseudodivergence excess type patients, 2.59 in convergence insufficiency type patients, and 5.47 in the normal group. Using the gradient method, the mean value of AC/A ratio was 1.47, 0.03, and 2.08 in each group, respectively. There was no statistically significant difference in mean values between patients with pseudodivergence excess type and the normal group, except when obtained using the gradient method (p = 0.43). CONCLUSIONS: A distinct difference in AC/A ratio existed when computed by the heterophoria method between patients with pseudodivergence excess type or convergence insufficiency type and the normal group. In the gradient method, however, the ratios of convergence insufficiency type patients were lower compared to the normal group, indicating the gradient method is more accurate than the heterophoria method.