Stability of refraction and visual acuity during 5 years in eyes with simple myopia. The PERK Study Group.

Background: Normal ranges of variability of refraction and visual acuity in adult myopic eyes are needed as a reference standard for assessing the stability of refractive corneal surgery.

Methods: We measured the changes in spectacle-corrected visual acuity and cycloplegic refraction during 5 years for the unoperated eye of 82 patients aged 21 to 57 years in the Prospective Evaluation of Radial Keratotomy Study. The changes were compared for contact lens and non-contact lens wearers. We also compared the 5-year cycloplegic and manifest refractions for these unoperated eyes.

Results: Of 77 eyes, 44% gained or lost one Snellen line and 48% experienced no change in spectacle-corrected visual acuity between baseline and 5 years. Only one eye (1%) lost two lines, and 7% gained two lines. The refractive change was less than 1.00 D for 84% of the 37 non-contact lens wearing eyes. Only 13% became more myopic by at least 1.00 D (maximum increase in myopia, 2.00 D), and 3% became less myopic by 1.00 D. Of 45 contact lens wearing eyes, 38% became more myopic by at least 1.00 D. The 5-year manifest refraction was 0.50 D to 1.50 D more myopic than the cycloplegic refraction for 37% of eyes.

Conclusions: We recommend using two or more Snellen lines as the standard for a meaningful change in spectacle-corrected visual acuity in operated eyes, and 1.00 D as a meaningful cutoff for stability of refraction. The wearing of contact lenses can confound the results of stability studies. The difference between the cycloplegic and manifest refractions suggests that the cycloplegic refraction should be used in planning for refractive surgery.