Corneal stromal changes induced by myopic LASIK

PURPOSE. Despite the rapidly growing popularity of laser in situ keratomile usis (LASIK) in correction of myopia, the tissue responses have not been th oroughly investigated. The aim was to characterize morphologic changes indu ced by myopic LASIK in human corneal stroma. METHODS. Sixty-two myopic eyes were examined once at 3 days to 2 years afte r LASIK using in vivo confocal microscopy for measurement of flap thickness , keratocyte response zones, and objective grading of haze. RESULTS. Confocal microscopy revealed corneal flap interface particles in 1 00% of eyes and microfolds at the Bowman's layer in 96.8%. The flaps were t hinner (112 +/- 25 mu m) than intended (160 mu m). The keratocyte activatio n in the stromal bed was greatest on the third postoperative dag. Patients with increased interface reflectivity due to abnormal extracellular matrix or activated keratocytes at greater than or equal to 1 month (n = 9) had si gnificantly thinner flaps than patients with normal interface reflectivity (n = 18; 114 +/- 12 versus 132 +/- 22 mu m, P = 0.027). After 6 months the mean density of the most anterior layer of flap keratocytes was decreased CONCLUSIONS. Keratocyte activation induced by LASIK was of short duration c ompared with that reported after photorefractive keratectomy. The flaps wer e thinner than expected, and microfolds and interface particles were common complications. The new findings such as increased interface reflectivity a ssociated with thin flaps and the apparent loss of keratocytes in the most anterior flap 6 months to 2 years after surgery may have important clinical relevance.