Myopic Surface Ablation in Asymmetrical Topographies: Refractive Results and Theoretical Corneal Elastic Response.

PURPOSE: To evaluate refractive results and the theoretical elastic response of photorefractive keratectomy in eyes with asymmetrical corneal surface and to compare such outcomes with a control-matched group of normal topographies.

DESIGN: Retrospective interventional case series with matched comparison group.

METHODS: Thirty eyes with superior-inferior dioptric difference (SI index) > 1.40 diopter (D) were compared to 30 eyes with normal topographies. Both groups were matched for age, preoperative spherical equivalent (SE), mean keratometry, and percentage of tissue altered (PTA). Refractive results and the theoretical elastic modulus calculations were evaluated.

RESULTS: The mean preoperative SI index in the asymmetrical group was 2.06 ± 0.56 D vs 0.14 ± 0.73 D in the control group (P < .001). From 3 to 12 months postoperatively, the asymmetrical group presented a mean re-steepening of 0.51 ± 0.39 D vs 0.19 ± 0.40 D in the control group (P = .014). The mean PTA of 14.42% generated a theoretical elastic modulus reduction of 10.25% in the asymmetrical group vs 2.45% in the control group (P = .006). The reduction of the theoretical elastic modulus correlated with the preoperative SI index (ρ = -0.387, P = .007). After 36 months, 90% of all eyes were within ±0.50 D of SE and the theoretical elastic modulus did not present a significant difference between both groups (P = .085).

CONCLUSIONS: Asymmetrical-topography corneas treated with myopic surface ablation presented an increased short-term keratometric re-steepening and reduction of the theoretical elastic moduli. The long-term follow-up indicated that, in selected cases of asymmetrical topographies, myopic surface ablation could induce a premature biomechanical elastic response rather than a progressive pathologic process.