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Is esophoria a factor in slowing of myopia by progressive lenses?
Brian Brown1, Marion H Edwards, Jackson T M Leung
1Centre for Eye Research, School of Optometry, Queensland University of Technology, Brisbane, Australia. brian@m141.aone.net.au
Purpose:
Our previous findings suggest that myopia can be slowed by wearing progressive lenses, and one possible mechanism for this is through the oculomotor system. We reanalyzed our findings to investigate the relationship between baseline oculomotor parameters and change in refraction, and between the change in these values and change in refraction.
Methods:
Children who wore progressive lenses (N = 38; 26 with +1.50 D addition, and 16 with +2.00 D addition) or single-vision lenses (N = 32) had refraction, distance heterophoria, near heterophoria, and stimulus AC/A ratio measured prospectively over a 2-year period.
Results:
There were no statistically significant correlations between baseline heterophoria or AC/A values and change in refractive error. Distance and near heterophoria did not change significantly over the 2 years of the experiment; AC/A ratio decreased significantly, but in an equivalent manner for both groups. In the combined progressive lens group, change toward more exophoria at near was associated with less myopia progression. However three-way analysis of variance (visit x lens type x esophoria/nonesophoria) showed significant main effects in refraction over all five visits. There was a significant interaction between lens type and visits; there was no significant interaction between lens type and esophoria/ nonesophoria grouping. Three-way analysis of variance showed a statistically significant decrease of AC/A ratio over all five visits; there was no interaction of visit by lens or visit by phoria grouping.
Conclusions:
Although there were no statistically significant differences between esophoric and nonesophoric subjects, there was only 46% as much myopia progression in the progressive lenses-esophoric group as in the progressive lenses-nonesophoric group. In addition, there were no differences in AC/A ratio between esophoric and nonesophoric subjects. However these findings are not definitive. This experiment was not designed to discriminate between refraction and oculomotor changes in esophoric and nonesophoric subjects and lacked the necessary statistical power to do so.