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 additional minus power in spectacles. Because excessive accommodation has been implicated as a cause of myopia, there is theoretical concern that overcorrecting minus lens therapy for exotropia may cause myopia.

OBJECTIVE

To investigate the effect of overcorrecting minus lens therapy for exotropia on the progression of myopia.

DESIGN

A retrospective chart review.

SUBJECTS AND METHODS

Seventy-four patients with intermittent exotropia were treated with overcorrecting minus lens therapy for at least 6 months (6-month treatment group), and a 34-patient subset of them received overcorrecting minus lens therapy for 5 years (5-year treatment group). The mean change in refractive error (spherical equivalent of the fixing eye) of these 2 groups 5 years after initial examination was compared with the mean change in refractive error of a control group of 45 patients with intermittent exotropia who did not receive overcorrecting minus lens therapy.

RESULTS

At the time of initial examination, the mean (+/-SD) refractive error 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 which were essentially identical. Five years after initial examination, the mean 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 error (myopic shift) were not statistically significant (t test), and the differences are clinically unimportant.

CONCLUSION

Overcorrecting minus lens therapy for intermittent exotropia does not appear to cause myopia.