Does overcorrecting minus lens therapy for intermittent exotropia cause myopia?

Background: Overcorrecting minus lens therapy has been used as a treatment for intermittent exotropia. It is based on the principle that an exotropic deviation will be decreased by stimulating accommodative convergence with a dditional minus power in spectacles. Because excessive accommodation has be en implicated as a cause of myopia, there is theoretical concern that overc orrecting minus lens therapy for exotropia may cause myopia. Objective: To investigate the effect of overcorrecting minus lens therapy f or exotropia on the progression of myopia. Design: A retrospective chart review. Subjects and Methods: Seventy-four patients with intermittent exotropia wer e treated with overcorrecting minus lens therapy for at least 6 months (6-m onth treatment group), and a 34-patient subset of them received overcorrect ing minus lens therapy for 5 years (5-year treatment group). The mean chang e in refractive error (spherical equivalent of the fixing eye) of these 2 g roups 5 years after initial examination was compared with the mean change i n refractive error of a control group of 45 patients with intermittent exot ropia who did not receive overcorrecting minus lens therapy. Results: At the time of initial examination, the mean (+/-SD) refractive er ror was 0.00 +/- 1.40 diopters (D) in the control group, 0.00 +/- 1.50 D in the study group, and -0.10 +/- 1.50 D in the 5-year study group, all of wh ich were essentially identical. Five years after initial examination, the m ean change in refractive error was -1.40 +/- 2.80 D in the control group, - 1.52 +/- 1.80 D in the 6-month treatment group, and -1.54 +/- 1.80 D in the 5-year treatment group. These differences in the change in refractive erro r (myopic shift) were not statistically significant (t test), and the diffe rences are clinically unimportant. Conclusion: Overcorrecting minus lens therapy for intermittent exotropia do es not appear to cause myopia.