OCT-guided femto lasers creates thin flaps

A study published in the January issue of the Journal of Refractive Surgery concluded that optical coherence tomography (OCT) could be a useful tool in guiding a femtosecond laser.
Omid Kermani, M.D., Augenklinik am Neumarkt, Cologne, who also presented the paper at the Lens, Refractive & Wavefront Summit in Alicante, Spain, in March 2009 said that thin-flap keratomileusis is a procedure that minimizes LASIK flap thickness to preserve both the corneal epithelium and the maximum residual stroma. He and his colleagues theorized that OCT could be used to guide the femtosecond laser to create a thin flap.
For the study, an in vitro investigation was performed on human autopsy eyes. Five human cadaver eyes, unsuitable for transplantation, underwent flap creation with a femtosecond laser, Dr. Kermani said. The laser procedure was controlled in real-time with an OCT system to ensure that the cut was placed just underneath Bowman’s layer. The repetition rate of the femtosecond laser was 10 MHz with a single-pulse duration of less than 400 femtoseconds (pulse energy in the nJ range). As a control, all eyes underwent histological dissection and were examined using light microscopy. Dr. Kermani said video monitoring of the flap creation supported the feasibility of real-time OCT monitoring of the femtosecond laser flap creation process. A clear distinction of the corneal epithelium was possible in all eyes. Bowman’s layer was not identified in all donor eyes at the given resolution of the OCT device used in this study. Light microscopy demonstrated flaps approximately 50-µm thick, confirming that the real-time monitoring assured a positioning of the cutting plane at minimum distance underneath Bowman’s layer. This study of five human cadaver eyes shows that real-time OCT monitoring of the creation of thin-flaps in LASIK using a femtosecond laser is possible, thus ensuring that the flap is created at the desired depth, Dr. Kermani and his colleagues concluded.