PURPOSE. To examine the corneal repair response after intrastromal femtosecond (fs) laser keratotomy. METHODS. Twelve rabbits underwent monocular intrastromal keratotomy performed with an fs laser at a preoperatively determined corneal depth of 160 to 200 m. The fs laserinduced corneal repair response was compared with that of nonoperated control eyes and eyes treated with photorefractive keratectomy (PRK). Follow-up examinations were performed 1, 3, 7, and 28 days after surgery. Corneas were

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... aluated using slit lamp, in vivo confocal microscopy, and light microscopy. The extracellular matrix components fibronectin and tenascin were located using immunofluorescence staining. Anti-Thy-1 and anti-␣-SMA antibodies and phalloidin were used to identify repair fibroblasts. Cell proliferation and nuclear DNA fragmentation were detected using an anti-Ki-67 antibody and the TUNEL assay, respectively. RESULTS. Intrastromal fs keratotomy resulted in a hypocellular stromal scar discernible as a narrow band of increased reflectivity on slit lamp examination. Deposition of fibronectin and tenascin as well as death and subsequent proliferation of keratocytes were observed. No differentiation of keratocytes into Thy-1-or ␣-SMA-positive fibroblasts could be detected. In contrast, after PRK, which causes epithelial and stromal wounding, all markers for repair fibroblasts were found in subepithelial stromal layers. On slit lamp examination, a fibrotic scar and a corneal haze were revealed. CONCLUSIONS. Isolated stromal injury using an fs laser avoids epithelial injury and is associated with a favorable woundhealing response preserving corneal transparency. Thus, fs laser keratotomy is a highly selective laser treatment that can be useful for the treatment of refractive errors. (Invest Ophthalmol Vis Sci.