Diurnal Change in Refraction, Corneal Curvature, Visual Acuity, and Intraocular Pressure After Radial Keratotomy in the PERK Study

Selected patients who complained of fluctuating visual acuity in the Prospective Evaluation of Radial Keratotomy (PERK) Study were examined before 8:00 a.m. and after 7:00 p.m. on the same day to determine diurnal change in uncorrected visual acuity, best corrected visual acuity, manifest refractive error, average central keratomeri power, and intraocular pressure. Sixty-three operated eyes were examined at three months, while 46 operated and 40 unoperated contralateral eyes were examined at one year after radial keratotomy. One year after surgery, 42% of the operated eyes had an increase in minus power of the manifest refraction of 0.50 to 1.25 diopters, 26% of the eyes changed their uncorrected visual acuity by 2 to 4 Snellen lines, and 35% of the operated eyes showed central steepening of the cornea by 0.50 to 1.25 diopters. These changes in the operated eyes at one year were similar to the changes at three months. Minimal diurnal changes occurred in the unoperated eyes at one year. Only 11 % of the unoperated eyes changed their manifest refraction by 0.50 to 1.00 diopters, none changed their uncorrected visual acuity by 2 to 4 Snellen lines, and only one of the unoperated eyes changed its central keratometric power by 0.50 diopters. This study documents that many patients who experience diurnal fluctuation of vision have steepening of the cornea and an increase in the minus power of their refraction during the day.