ANALYSIS OF CORNEAL TOPOGRAPHY AFTER EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY

Excimer laser photorefractive keratectomy (PRK) is an effective treatm ent for myopia. We investigated the magnitude of optical zone decentra tion and qualitative patterns of corneal topography after this treatme nt. We performed computer-assisted videokeratography on 44 myopic eyes (29 patients) that had undergone PRK before and 1, 6, and 12 months a fter the procedure. Associations of clinical outcomes with decentratio n and topographic patterns were assessed. The normalized scale of the topography 1 month postoperatively showed a mean decentration of 0.33 +/- 0.23 mm (range 0-0.9). Thirty-four eyes had decentration of less t han 0.50 mm; 10 had an ablation zone decentered from 0.5 to 0.9 mm. An alysis of geometric mean visual acuities between eyes with less than 0 .5 mm decentration and those with 0.5 to 0.9 mm decentration demonstra ted minimal differences. No eye was decentered more than 1 mm. Four ma in ablation patterns were noted on subtraction analysis: homogeneous, semicircular, keyhole, and central island. Over time, the number of ey es with a homogeneous pattern increased. Eyes with a homogeneous ablat ion pattern had significantly better uncorrected visual acuity than th ose with other patterns. The mean visual acuity was 20/29.1 in the hom ogeneous group and 20/38.5 in the pooled irregular group 1 month posto peratively (p < 0.05). There was no significant difference among the f our ablation patterns at 6 or 12 months after PRK. Topographic pattern s were not significantly associated with best-corrected vision.