Biomechanical changes in the cornea caused by refractive surgery

In order to provide a customized correction that is unique for each patient, the predictability of a refractive surgery procedure must be improved. LASIK, currently the method of choice for laser refractive surgery procedures, is a complex surgical technique with several variables that can significantly affect the outcome of the procedure. One way to optimize a customized procedure is to develop an optical and biomechanical model of how the cornea responds to the cutting of a flap and the subsequent excimer laser ablation. However, these two effects must first be considered separately as they each have different impacts on the overall procedure. Much is already known about the effects of a laser ablation on the cornea. Surgeons and laser companies base and modify their ablation routines on large statistical analyses of ablations performed over many eyes. Unfortunately, this is not a suitable approach for a customized ablation, as these same algorithms are models that are determined based on a mean population response instead of an individual, patient by patient response. In attempts to explore and possibly improve the predictability of a LASIK procedure for each patient, we are conducting research to examine each component of a laser ablation procedure and its effect on the overall patient outcome.

One such project, carried out by Jason Porter and colleagues (2003), compared optical and biomechanical responses of the cornea to the cutting of a corneal flap in the absence of a subsequent laser ablation. This study allowed us to separate systematic changes in the eye's aberrations and corneal shape as a result of the microkeratome incision, from changes induced by laser ablation of the corneal stroma. The predictability of such changes is crucial for assessing whether LASIK should be the technique of choice for delivering a customized correction for all of the eye's aberrations.

In addition, we are working with Krystel Huxlin, Jay Wang, and Lana Nagy to better understand the cellular contribution to corneal biomechanics, as pertains to the corneal reaction to laser refractive surgery. Dr. Huxlin's lab has developed an animal model in which optical changes, measured with a wavefront sensor, can be correlated with structural and cellular changes in the cornea after the laser ablation. By understanding the cellular contribution to lower and higher order optical aberrations induced by laser refractive surgery, we are moving closer to the possibility of delivering perfectly customized ablations.