Comparison of methods for determining the AC/A ratio in accommodative esotropia

The two most commonly used clinical methods of determining a high AC/A ratio are: 1) the gradient method, and 2) the distance/near disparity method. Significant differences can be found not only between these two methods, but also in the different techniques for the gradient method alone. The purpose of our study is to compare the gradient method using +3.00 lenses for near and -3.00 lenses for distance, and the distance/near disparity method.

Patients examined over a 2-year period (1995-1997) with a high AC/A ratio esotropia according to the distance/near disparity were grouped according to level of high AC/A ratio, then prospectively measured by the gradient method (using plus lenses for near and minus lenses for distance). All measurements were performed with full spectacle correction in place according to cycloplegic refraction, and with fixation on an accommodative target.

Forty-five patients were included. Using both plus and minus lenses, a high AC/A ratio by the gradient method was found in 16 (36%) patients, (2 [12%] with a grade 1; 7 [44%] with a grade 2; and 7 [44%] with a grade 3, by the distance/near disparity method), a normal ratio was found in 6 (13%), and no patient had a low ratio. Twenty-three patients fell into a different category of AC/A ratio using plus lenses for near compared with minus lenses for distance.

The distance/near disparity method appears to diagnose a high AC/A ratio much more frequently than the gradient method. There was some variability in the AC/A ratio with plus versus minus lenses when the gradient method was used. Further study using the gradient method in patients without a significant distance/near disparity is required.