Fewer aberrations with larger ablation zone, study says

NEW ORLEANS — Corneal optical aberrations after photorefractive keratectomy with a large ablation and transition zone are less pronounced than with a smaller zone with no transition, according to a study here. Also, optical aberrations decreased postoperatively when measured with smaller pupils and increased when measured with larger pupils, the authors said.

Researchers at the LSU Eye Center used videokeratographs to calculate the wavefront variance of the corneas for both 3-mm and 7-mm pupils. Measurements of 72 eyes treated for low to moderate myopia were taken preop and at 1, 3, 6, 12 and 18 months postop.

All optical aberrations decreased postop for 3-mm pupils and increased for 7-mm pupils compared with preop values. For 3-mm pupils, the lower-order optical aberrations decreased postop and never returned to preop values. Similarly, higher-order aberrations decreased throughout the postop period as well.

For 7-mm pupils, coma-like aberrations increased slightly and spherical-like aberrations increased by nearly an order of magnitude during the postop period. Higher order aberrations increased slightly as well.

Total wavefront aberrations decreased an average of 2.3 times postop for 3-mm pupils and increased significantly (P < .05) at all postop exams for 7-mm pupils.

Additionally, opening the pupil from 3 mm to 7 mm before surgery produced a 14-fold increase in total aberrations, whereas this same change produced an average 113-fold increase after photorefractive keratectomy.

The study is published in the Archives of Ophthalmology.