Purpose : To assess and to compare stromal and endothelial changes at the cellular level in patients who had photorefractive keratectomy (PRK) and laser in situ keratomileusis (LASIK) using in vivo confocal microscopy

Methods : In this semiexperimental study, 32 eyes of 16 patients (4 males and 12 females) with low to moderate myopia [-1.00 to -4.50 diopters (D)] or low to moderate myopic astigmatism (a total below 4.50 D and a max astigmatism of 1.50 D) were investigated. All participants had the history of PRK or LASIK surgery and were examined with Confoscan 3 confocal microscope ( Nidek , Japan ) before and 6 months after surgery. The densities of the keratocytes in the anterior and posterior stroma and the endothelial cell count (ECC) were measured. Finally the collected data was analyzed by SPSS16 and T-test.

Results : The mean ablation depth in LASIK and PRK groups were 61.00±17.17 and 62.13±15.4 μm, respectively. Six months after surgery, the mean cell density change in anterior and posterior stroma in LASIK group was 367.12±103.35 cells/mm² (34.7% reduction) and 9.25±28.28 cells/mm² (1.31% reduction) respectively. In the PRK group, these values were respectively 319.71±83.45 cells/mm² (31.13% reduction) and 0.17±38.97 cells/mm² (0.02% reduction). The ECC increased by 0.27% and 1.39% in LASIK and PRK groups, respectively. At retroablation zone in LASIK group, the mean number of keratocytes decreased by 37.2%.

Conclusion : By Confoscan application, after both PRK and LASIK, a decrease in the number of stromal keratocytes which was more significant in the anterior stroma was found. On the other hand, there was a slight increase in the ECC compared to preoperative counts which may be attributed to counting errors. There was not any significant difference in stromal cell densities and the endothelial cell counts between LASIK and PRK groups.