LASIK After PRK for Myopic Regression

In their recent article,1 Özdamar and coauthors reported the results of laser in situ keratomileusis (LASIK) after photorefractive keratectomy (PRK) for myopic regression. During the PRK procedure for myopia (range −5.50 to −16.00 diopters [D], mean −10.80 ± 3.25 D), the corneal thickness decreases according to Munnerlyn's formula (ablation depth = square of diameter of ablation zone × diopter of correction/3). Corneal topography values will also change during PRK. When performing LASIK after a 18.5 ± 8.2 month follow-up for myopic regression (range −1.50 to −12.50 D, mean −5.96 ± 3.06 D), we would like to emphasize the importance of corneal pachymetry and topography, which are not mentioned properly in the article. Prior to LASIK, it is very important to assess the corneal curvature by corneal topography and to ensure adequate corneal thickness by measuring with the corneal pachymeter. During the PRK procedure, Bowman's layer, which has about a 12 μm thickness, is partially or completely ablated according to the degree of myopia. Since Bowman's layer is an important factor in maintaining the shape and stability of the cornea, adequate residual corneal thickness becomes more important in corneas that have LASIK after PRK. It has been recommended that at least 200 μm of posterior stromal tissue be left after the LASIK procedure to avoid loss of integrity of the cornea and subsequent development of corneal ectasia. Without knowing the thickness of a cornea that had PRK, LASIK cannot be properly done. Yaşar Sakarya MD Ertugrul Cüneyt Işik MD Samed Sitki Ermiş MD Istanbul, Turkey