Diurnal fluctuations in corneal topography 10 years after radial keratotomy in the Prospective Evaluation of Radial Keratotomy study

Purpose: To correlate clinically observed fluctuations in manifest refracti on, visual acuity, keratometry, and intraocular pressure (IOP) with changes in the anterior corneal surface as measured by videokeratography in patien ts 10 years after radial keratotomy (RK). Setting: Four clinical centers in the United States that participated in th e Prospective Evaluation of Radial Keratotomy (PERK) study. Methods: Thirty-two eyes of 20 PERK patients who noted diurnal fluctuations in vision had clinical examination and videokeratography (TMS-1, Computed Anatomy Inc.) in the morning and evening of the same day a mean of 10.3 yea rs (range 7.8 to 11.7 years) after RK. The videokeratographs were analyzed in terms of various indexes generated by custom-designed software. Morning- to-evening changes in the means of the various clinical and videokeratograp hic values were assessed using pairwise methods. Results: The mean increase in myopia was 0.36 diopters (D) +/- 0.58 (SD) fr om morning to evening (P < .01). Analysis of the videokeratographs showed a corresponding increase in average corneal power (ACP), reflecting a steepe ning of 0.52 +/- 0.45 D (P < .001). The change in ACP was correlated with a change in the manifest spherical equivalent refraction (R = 0.39, P = .03) and a change in best spectacle-corrected visual acuity (R = 0.38, P = .03) over the same period. Similarly, simulated keratometry (SimK) readings cor related with the change in the manifest spherical equivalent refraction (R = 0.38, P = .03 for SimK1; R = 0.37, P = .35 for SimK2; R = 0.4, P = .02 fo r average SimK), although the standard clinical keratometric data did not ( P = .26 for K1, P = .11 for K2, and P = .09 for the mean K). The elevation depression magnitude, a measure of the low-frequency irregularities of the cornea, showed a decrease of 0.32 +/- 1.59, which also correlated with the change in the manifest spherical equivalent refraction (R = 0.37, P = .04). Intraocular pressure tended to decrease from morning to evening (mean chan ge of -0.97 +/- 3.29 mm Hg), but the difference was not significant. Variat ions in IOP in individual patients, however, were correlated with changes i n the manifest spherical equivalent refraction (R = 0.37, P = .04). Conclusions: Diurnal fluctuations in corneal topographic indexes can be use d to evaluate the diurnal fluctuations in refraction and visual acuity afte r RK. The study findings provide statistical support for the idea that IOP contributes to the diurnal fluctuation in visual acuity after RK. J Catarac t Refract Surg 1999; 25:904-910 (C) 1999 ASCRS and ESCRS.