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purpose. Despite the rapidly growing popularity of laser in situ keratomileusis (LASIK) in correction of myopia, the tissue responses have not been thoroughly investigated. The aim was to characterize morphologic changes induced by myopic LASIK in human corneal stroma.

methods. Sixty-two myopic eyes were examined once at 3 days to 2 years after 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 100% of eyes and microfolds at the Bowman’s layer in 96.8%. The flaps were thinner (112±25 μm) than intended (160 μm). The keratocyte activation in the stromal bed was greatest on the third postoperative day. Patients with increased interface reflectivity due to abnormal extracellular matrix or activated keratocytes at≥ 1 month (n= 9) had significantly thinner flaps than patients with normal interface reflectivity (n= 18; 114±12 versus 132±22 μm, 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 compared with that reported after photorefractive keratectomy. The flaps were thinner than expected, and microfolds and interface particles were common complications. The new findings such as increased interface reflectivity associated 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.