Diurnal variation in refraction after excimer laser photorefractive keratectomy

Diurnal fluctuations in vision are common after radial keratotomy (RK), associated with a myopic change in refraction and keratometric power mostly in the morning. After photorefractive keratectomy (PRK), only a small percentage of patients report fluctuations of vision. We tested ten such patients who had undergone excimer laser PRK with regard to refraction, keratometry, and visual acuity 5 to 20 months after surgery. Patients were examined five times during one day from 8:00 a.m. to 8:00 p.m. Ten volunteers serving as a control group were examined following the same protocol. None of the patients showed an increase in minus spherical power of the manifest refraction between morning and evening. The change in manifest refraction from morning to evening was +0.3 D +/- 0.3 D, which was not significantly different from the control group. The change in refraction did not correlate with keratometric power, follow-up time of age of the patients.