Posterior steepening and prolateness of the posterior corneal surface occurred shortly after myopic LASIK, but these values returned to normal levels between 1 and 3 months postoperatively, a study found.
“Histopathologic and ultrastructural studies of corneas that developed ectasia after keratorefractive surgery have shown that the primary effect of the biomechanical failure process occurs in the posterior corneal stroma,” the study authors said. “A good understanding of how the biomechanical response affects the posterior corneal surface in keratorefractive procedures is thus becoming important for early recognition of induced ectatic disorders.”
The prospective study included 80 healthy eyes of 46 patients who underwent LASIK. Ablation depth was more than 100 µm in 18 eyes of 11 patients, between 50 µm and 99 µm in 38 eyes of 21 patients, and less than 50 µm in 24 eyes of 14 patients.
Posterior eccentricity and central, paracentral and peripheral posterior corneal curvature were measured preoperatively and 1 day, 1 week, 1 month and 3 months postoperatively.
Study results showed posterior surface steepening and a shift toward prolateness in all groups. These parameters peaked within 1 week and subsided to baseline values after 1 month.
The group with 100 µm or more of ablation had a statistically significant change in the central posterior cornea after the first day (P = .03). The change was significantly higher than those in the group with 50 µm to 99 µm of ablation (P = .02) and the group with less than 50 µm of ablation (P < .01). The change was insignificant after 3 months.
“The degree of change was related to the amount of anterior tissue severed,” the authors said.