Corneal topography of photorefractive keratectomy versus laser in situ keratomileusis

Abstract

Objective

This study aimed to compare qualitative patterns of corneal topography early in the postoperative course after excimer laser photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) when used for the treatment of myopia of 6.0 to 15.0 diopters.

Design

The study design was a prospective, multicenter, randomized clinical trial.

Participants

A total of 64 eyes were treated with PRK and 54 eyes were treated with LASIK.

Intervention

Using the Summit Apex excimer laser, patients received either PRK or LASIK using a single pass, multizone excimer laser ablation. Computer-assisted videokeratography was performed at designated postoperative examinations.

Main outcome measures

Videokeratography maps at 1 and 3 months after surgery were classified using a standard classification scheme. The association of topography patterns to loss of spectacle-corrected visual acuity was tested.

Results

At 1 month, for the PRK (n = 60) and LASIK (n = 51) groups, respectively, 63.3% and 19.6% of eyes fell into one of the four optically irregular groups (central island, keyhole, semicircular, or irregularly irregular; P < 0.001). At 3 months, for the PRK (n = 49) and LASIK (n = 39) groups, respectively, 36.7% and 10.3% of eyes fell into one of the optically irregular groups (P = 0.004). Comparing the 1- and 3-month examination results in the PRK and LASIK groups, respectively, 19 (42%) of 45 eyes and 11 (31%) of 36 eyes had a change in topography, generally to an optically smoother pattern. The irregular groups, taken together, were associated with a greater tendency toward loss of spectacle-corrected visual acuity of two or more Snellen lines (P = 0.01). There also was greater tendency toward loss of spectacle-corrected visual acuity in the PRK group that diminished with time (P < 0.01 at 1 month, P = 0.05 at 3 months).

Conclusions

After treatment for moderate-to-high myopia, LASIK topography patterns generally are more regular than are PRK patterns. This may be a result either of masking of underlying topography perturbations by the lamellar corneal flap, thus mitigating induced topography changes, or differences in surface wound healing. This study suggests that more rapid return of spectacle-corrected visual acuity found in patients treated with LASIK may be a result of more regular topography patterns early in the postoperative course.