New method measures corneal changes following LASIK

Paris—The proper thickness of the corneal flap and stromal bed after LASIK is an important factor in the physician's decision for repeated refractive surgery. Sergei Rebrikov, MD, of Russia reported on a method of evaluating corneal anatomical changes after LASIK over a long-term period.

Dr. Rebrikov studied 70 eyes of 35 patients following LASIK, with a planned flap thickness of 160 µm. The patients were evaluated before surgery and postoperatively at 1 day and 1, 3, and 12 months. The flap was made with a Hansatome microkeratome (Bausch & Lomb) and the surgeries were performed with MEL-70 G-scan laser (Carl Zeiss Meditec).

Using optical coherence tomography (OCT-3, Carl Zeiss Meditec), Dr. Rebrikov gathered the results from graph analogous and transferred them to A-scan graphs. The first peak of the graph corresponded to the epithelium surface; second, to the interface between the corneal flap and the stromal bed; and third, to the endothelium surface. Distances between the peaks represented the corneal flap, stromal bed, and corneal thickness within an accuracy of 4 µm.

Results of the study showed that the mean corneal thickness before surgery was 529 µm. Postoperatively, the mean corneal thickness at 1 day was 435 µm. At 1 month, it was 439 µm; at 3 months, 442 µm; and at 12 months, 477 µm. Mean corneal flap of 138 µm was consistent throughout the same follow-up periods. Mean stromal bed thickness at 1 day was 294 µm, 1 month at 298 µm; 3 months at 301 µm, and 12 months at 306 µm.

Dr. Rebrikov concluded that it is possible that this method is highly accurate in determining the proper thickness of the corneal flap and stromal bed following the initial LASIK procedure up to 1 year. Theoretically, these results may change the approach to indications of repeated refractive surgery, he added.