Corneal topography of small-beam tracking excimer laser photorefractive keratectomy

Purpose: To evaluate the topographic characteristics of photorefractive ker atectomy (PRK) for low myopia performed with a small-beam (0.9 mm) tracking excimer laser. Setting: Department of Ophthalmology, LSU Eye Center, Louisiana State Unive rsity Medical Center School of Medicine in New Orleans, and the Refractive Surgery Center of the South at the Eye, Ear, Nose, & Throat Hospital, New O rleans, Louisiana, USA. Methods: Sixty-seven eyes of 47 patients had PRK with a small-beam tracking laser. Of these, 49 eyes had data permitting evaluation of ablation centra tion; usable data for topographic analysis were available for 59 eyes preop eratively, 54 eyes at 1 month, 42 eyes at 3 months, and 25 eyes at 6 months , permitting measurement of various topographic parameters, including the c ylinder (CYL), average corneal power (ACP), surface regularity index (SRI), surface asymmetry index (SAI), corneal eccentricity index (CEI), and coeff icient of variation of corneal power (CVP). Results: Preoperatively, all eyes were topographically normal. Postoperativ ely, no eye exhibited a "central island" by even the least-restrictive defi nition, and all eyes had best spectacle-corrected visual acuities (BSCVAs) of 20/20 or better at all follow-ups. Mean decentration of the ablations fr om the pupil centers was 0.42 mm +/- 0.28 (SD) (n = 49). There was no corre lation between measured decentration and BSCVA (P =.46). The central cornea was flattened (decreased ACP; P <.001) and made oblate (decreased CEI; P < .001) as expected. There was no increase in SRI or SAI (irregular astigmati sm) at 6 months compared with preoperative values (P =.91); however, CYL an d CVP (varifocality) increased slightly (P =.04 and .02, respectively). Conclusion: The absence of significant regular or irregular astigmatism 6 m onths after PRK with the small-beam laser is an improvement over published results achieved with wide-beam lasers and is consistent with the excellent visual acuity results in this cohort. J Cataract Refract Surg 1999; 25:675 -684 (C) 1999 ASCRS and ESCRS.