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

Purpose: 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 met hods, but also in the different techniques for the gradient method alone. T he purpose of our study is to compare the gradient method using +3.00 lense s for near and-3.00 lenses for distance, and the distance/near disparity me thod. Methods: Patients examined over a 2-year period (1995-1997) with a high AC/ A ratio esotropia according to the distance/near disparity were grouped acc ording to level of high AC/A ratio, then prospectively measured by the grad ient method (using plus lenses for near and minus lenses for distance). All measurements were performed with full spectacle correction in place accord ing to cycloplegic refraction, and with fixation on an accommodative target . Results: Forty-five patients were included. Using both plus and minus lense s, 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 dif ferent category of AC/A ratio using plus lenses for near compared with minu s lenses for distance. Conclusions: The distance/near disparity method appears to diagnose a high AC/A ratio much more frequently than the gradient method. There was some va riability in the AC/A ratio with plus versus minus lenses when the gradient method was used. Further study using the gradient method in patients witho ut a significant distance/near disparity is required.