Diurnal cycle of refraction after radial keratotomy.

A single patient was refracted 1000 times at all hours of the day in the year after bilateral radial keratotomy (RK). Preoperatively, there was practically no diurnal variation of refraction. Postoperatively, the refraction showed a myopic shift of several diopters from early morning to late evening. Transient hyperopia was superimposed on this diurnal cycle of refraction, peaking two weeks postoperatively, and a smaller long-term hyperopic shift was evident 1 year postoperatively.