PURPOSE: To analyze the incidence, clinical course, and possible mechanisms of epithelial ingrowth after laser in situ keratomileusis (LASIK). DESIGN: Interventional case series. METHODS: Retrospective evaluation of 4,867 eyes of 2,502 patients who had LASIK. The type of microkeratome (LSK-One or MK-2000), corneal flap thickness, and clinical course were analyzed. We also compared the cutting characteristics of both microkeratomes in pig cadaver eyes by scanning electron microscopy. RESULTS: The frequency of epithelial ingrowth was significantly greater in the MK-2000 (34 of 1,680 eyes; 2.0%) than the LSK-One group (30 of 3,187 eyes; 0.94%; P = .001). In 24 eyes (37.5%), blood, cell infiltration, ointment under the corneal flaps, or epithelial defect were detected at the area of epithelial ingrowth postoperatively. The incidence of epithelial ingrowth was correlated with the incidence of epithelial defect during surgery (P < .001) and with incidence of diffuse lamellar keratitis after surgery (P = .003). Flap thickness was thinner in eyes with epithelial ingrowth (126.0 ± 29.1 μm) compared with flap thickness in eyes without epithelial ingrowth (133.8 ± 27.3 μm; P < .001). Scanning electron microscopy showed clear differences in the appearance of flap edges created by the two types of microkeratomes. Epithelial ingrowth disappeared or remained unchanged in 54 eyes (90%) and progressed in six cases (10%). CONCLUSIONS: Poor adhesion caused by excessive hydration due to epithelial defect as well as by foreign bodies between the flap stromal bed and thickness and morphologic characters of the corneal flap, depending on the type of microkeratomes, are related factors for development of epithelial ingrowth.
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