The analysis of AC/A ratio in nonrefractive accommodative esotropia treated with bifocal glasses

Abstract

Purpose : To report the long term results of bifocal treatment and analyze the change of accommodative convergence to accommodation (AC/A) ratio according to the result of treatment in patients with nonrefractive accommodative esotropia and find out the early factors that predict the result of bifocal treatment. Materials and Methods: Sixteen patients who were treated with bifocal glasses with follow-up of more than 5 years were retrospectively evaluated. At each visit, data of near and distance deviation, refractive error, the AC/A ratio by the lens gradient method and bifocal treatment were collected. We analyzed these data after divide into two groups as the result of bifocal treatment, which consist of bifocal stop group and bifocal continue group.Results : Six patients (38%, bifocal stop group; BSG) were able to stop using bifocal glasses at an average age of 10.8 years (range, 6.5-15.4 years) during their follow up. However, the other ten patients (62%, bifocal continue group; BCG) had to continue using bifocal glasses until the last visit at an average age of 13.8 years (range, 11.3-18.5 years). The AC/A ratio decreased from time of the bifocal prescription to the last visit in both groups, from 4.4 to 2.7 in BSG and from 5.9 to 4.5 in BCG. AC/A ratios were significantly higher in BCG than that of BSG from the beginning of bifocal treatment (p=0.03) and this difference was persistent until the final visit (p=0.03).Conclusion : About one-third of patients with nonrefractive accommodative esotropia who were treated with bifocal glasses were able to stop using bifocal glasses without surgery. The average age of bifocal stop was 10.8 years, which may indicate that surgical treatment of nonrefractive accommodative esotropia to eliminate the need for bifocal glasses should be deferred until patients are at least this age. The AC/A ratio decreased with age in both groups but AC/A ratio in BCG was significantly higher than that of BSG throughout the entire follow up period. AC/A ratio at bifocal prescription could be an important factor in predicting response to bifocal treatment. In our study, all the AC/A ratio of bifocal stop group were less than 5.5 at bifocal prescription.