Topographic assessment of irregular astigmatism after photorefractive keratectomy

Objective: To correlate new quantitative topographic indexes of corneal irregular astigmatism to best spectacle-corrected visual acuity (BSCVA) following excimer laser photorefractive keratectomy (PRK). Setting: Department of Ophthalmology, LSU Eye Center, and Refractive Surgery Center of the South, Ear, Nose and Throat Hospital, New Orleans, Louisiana; Manhattan Eye, Ear and Throat Hospital, New York, New York, USA. Methods: Videokeratography data (TMS-1) were obtained preoperatively and 1, 3, 6, 12, 18, and 24 months postoperatively from 100 eyes having PRK for low to mild myopia. Algorithms measured fine local irregularity with the surface regularity index (SRI(p)), varifocality with the coefficient of variation of corneal power (CVP(p)), and central islands with the elevation/depression magnitude (EDM). Results: The SRI(p) and CVP(p) increased after surgery and remained significantly higher than the preoperative levels throughout the 24 month follow-up (P < .05). The increase in EDM was significant from 1 to 6 months (P < .05) but not thereafter. Multiple regression analysis revealed that variables having a statistically significant relationship with postoperative BSCVA were CVP(p) and EDM at 1 month, CVP(p) at 3 months, and CVP(p), haze, and age at 6 months. No statistically significant correlation between any measures of irregular astigmatism and BSCVA was found after 1 year of follow-up. Conclusion: The quantitative measures used in this study are sensitive methods by which irregular astigmatism after keratorefractive procedures can be classified, evaluated, and compared.