Topography of PERK corneas at 10 years

Purpose. To correlate videokeratographic measures of irregular astigmatism to best spectacle-corrected visual acuity (BSCVA) among eyes of the Prospective Evaluation of Radial Keratotomy (PERK) Study at the 10-year postop exam. Methods. Four PERK study centers-Emory, LSU, USC, Minnesota-contributed TMS (Tomey) topographic exams on 274 operated eyes. The color-coded maps were classified and custom software was used to tabulate multiple topographic indexes related to irregular astigmatism. Results. Average decentration of the treated areas was 0.40±0.26mm (max=1.53mm) with no preferential direction for decentration. Topography classification: normal 1.1%; round 8.4%; polygonal 18.6%; symmetric howtie 11.7%; asymmetric bowtie 7.7%; irregular 8.8%; mild central flattening 43.0%; markedly decentered flattening 0.7%. Statistically significant (p<0.0001) negative correlations between topographical indexes and the 10-year BSCVA by manifest refraction (TVAMAN) were obtained for the simulated keratometric cylinder (CYL;r=0.30), the Coefficient of Variation of corneal Power over the pupil (CVP;r=0.30), and the Elevation/Depression Magnitude (r=0.28). Other statistically significant negative correlations (p<0.05) included the Surface Regularity Index (r=0.18), Surface Asymmetry Index (r=0.17), Corneal Eccentricity Index (r=0.13), and Irregular Astigmatism Index (r=0.15). A stepwise regression model indicated that 14% of the limited variation in TVAMAN (20/10-20/32) could be accounted for by the variables CYL and CVP. Conclusions. The 10-year PERK corneas generally had excellent BSCVA and surgically induced irregular astigmatism was not a complication in this group. Videokeratography is a sensitive method for assessing irregular astigmatism after refractive surgery.