Analysis of corneal topography after automated lamellar keratoplasty

The purpose of the study is to evaluate the effects of myopic automated lamellar keratoplasty (ALK) on corneal topography.

The authors performed a retrospective study of computer-assisted topographic maps obtained before surgery and at the last follow-up visit of 9 patients (13 eyes) who underwent ALK without enhancement to correct moderate-to-high myopia during a 12-month period.

Follow-up ranged from 3.5 to 13 months (mean, 5.8; standard deviation, 3.1). The mean manifest spherical equivalent changed from -10.5 +/- 2.2 diopters (D) before surgery to -1.1 +/- 1.8 D at the last follow-up visit. Mean simulated keratometry (Sim K) decreased from 45.6 +/- 1.9 D to 38.9 +/- 2.7 D. Mean corneal astigmatism increased from 1.3 +/- 0.8 D to 2.1 +/- 0.9 D. The mean surgically induced cylinder vector (calculated by vector analysis) was 1.1 +/- 0.6 D. Mean surface regularity index (SRI) and surface asymmetry index (SAI) increased from 0.37 +/- 0.38 and 0.32 +/- 0.43 before surgery to 1.00 +/- 0.32 (P < 0.001) and 0.75 +/- 0.36 (P = 0.01), respectively, at the last visit. A positive correlation was observed between the decrease in mean Sim K and the increase in manifest spherical equivalent (reduction of myopia) (r = 0.77, P = 0.002), increase in SRI (r = 0.73, P = 0.005), and increase in SAI (r = 0.58, P = 0.04). The change in manifest spherical equivalent was significantly less than the change in Slm K (P < 0.001).

Myopic ALK significantly flattens the cornea and reduces myopia. However, it induces corneal astigmatism and decreases corneal surface regularity and symmetry. The degree of myopic correction, as well as the surgically induced corneal surface irregularity and asymmetry, is positively correlated with the amount of corneal flattering derived from the surgical procedure.