[In vivo confocal microscopy evaluation of corneal changes induced after LASIK using the IntraLase femtosecond laser...

To assess stromal modifications occurring after IntraLase femtosecond laser for laser in situ keratomileusis (LASIK) using the Heidelberg retina tomograph II/Rostock cornea module.

Twelve eyes from six patients were examined using the Heidelberg retina tomograph II cornea module after IntraLase femtosecond laser: ten eyes were examined at 1 week and 2 months after laser surgery, including four eyes examined at day 1, and two eyes examined at day 2. Morphological modifications of the corneal stroma, flap interface, and flap margin were evaluated at these different times and compared with the mechanical microkeratome interfaces of five patients (ten eyes), using the same technique at the same periods after the surgical intervention.

Evaluations at days 1 and 7 showed simultaneous depletion and activation of keratocytes on both sides of the interface. We also observed some brightly reflecting particles together with scattered, less bright dots, from day 7 and increasing after 2 months. Some clinically visible deposits at the level of the interface were observed at the periphery of the flap at day 1 and could represent cell-degradation products. With confocal microscopy, they appeared as homogeneous reflective deposits with a larger size than that of particles; they had decreased at month 2. The flap margin appeared microscopically as a very clear-cut edge, including epithelial cells, while those performed with a mechanical microkeratome appeared more like a poorly limited fibrotic scar. We also observed a secondary fibrotic reaction at month 2, adjacent to the still well-defined IntraLase flap edge.

This study showed substantial morphological similarity between the interfaces obtained with femtosecond laser and mechanical microkeratome. The discovery of brightly reflecting particles in the IntraLase interface goes against the hypothesis of the metallic origin of these deposits. The flap margin microscopically looked extremely well delimited, but seemed to provoke an adjacent secondary fibrotic reaction, both microscopically and macroscopically, greater at 2 months than after a mechanical microkeratome cut.