Real-Time Optical Coherence Tomography-Guided Femtosecond Laser Sub-Bowman Keratomileusis on Human Donor Eyes

Abstract

To determine the usefulness of optical coherence tomography (OCT) as a tool in guiding the femtosecond (fs) laser in the creation of a sub-Bowman keratomileusis (SBK) flap in human eyes. A nonrandomized case series. In a private research laboratory setting, we performed an in vitro investigation on human autopsy eyes. Five human cadaver eyes, unsuitable for transplantation, underwent flap creation with a fs laser. The laser procedure was controlled in real-time with an OCT system (Thorlabs HL AG, Luebeck, Germany) to ensure that the cut was placed just underneath the Bowman layer. The fs laser worked at a repetition rate of 10 MHz with a single-pulse duration of < 400 fs (pulse energy in the nanoJoule range). As a control, all eyes underwent histologic dissection (toluidine blue) and were examined using light microscopy (LM). Video monitoring of the flap creation supported the feasibility of real-time OCT monitoring of the fs laser flap creation process. A clear distinction of the corneal epithelium was possible in all eyes. The Bowman membrane was not identified in all donor eyes at the given resolution of the OCT used in this study. Still, LM examination confirmed that the real-time monitoring assured a positioning of the cutting plane at minimum distance underneath the Bowman layer. This small laboratory test offers evidence that real-time OCT monitoring of creation of a SBK flap using a fs laser is possible, thus ensuring that the flap is created at the proper depth.