Cryorefractive surgical procedures (keratomileusis, keratophakia, and epikeratophakia) have gained popularity in the ophthalmic community and among the general public because of their potential to correct refractive errors of the eye. These surgeries are fraught with numerous problems, including delayed visual recovery, interface scarring, irregular astigmatism, and poor predictability. Delayed visual recovery, which correlates with a loss of clarity of the cryolathed cornea, is the most significant problem with visual rehabilitation taking up to eighteen months in many cases and with permanent visual loss reported in some cases. While technical improvements may reduce the problems of astigmatism and predictability, the problems of delayed visual recovery and interface scarring will only be solved by a better understanding of the short and long term effects of cryorefractive surgeries on the cornea. While the goal of this research effort is to improve the cryorefractive surgical procedures so that visual rehabilitation is prompt, and the problems of interface scarring, irregular astigmatism and poor predictability are eliminated, the thrust of this research has been focused on studies of the cell biology of the keratocyte during and after a cryolathe freeze using a rabbit model of lamellar refractive keratoplasty. These studies have already demonstrated that keratocyte repopulation is corellated with the return of clarity of the cryolathed lenticule. The studies are focused on determining the optimal freezing and lathing parameters for keratocyte survival, since experimental evidence suggests the techniques which enhance keratocyte survival also enhance corneal clarity following a cryolathe freeze. Freeze and thawing rates, cryoprotectants, and lathing parameters will be varied; and keratocyte viability (keratoctye viability assay, LKP model), cornea clarity (LKP model), and corneal morphology (epithelium, extracellular matrix, and endothelium) will be evaluated. The successful completion of these studies will provide important new information about the cell biology of the keratocyte exposed to freeze injury. This information, if directly applied to the cryolathing surgical techniques, may improve the results of these surgeries by, specifically, shortening the postoperative visual rehabilitation time. Although this goal directed research is focused on enhancing keratocyte survival following a cryolathe freeze, these studies will also provide basic information about the cryobiology of the keratocyte and corneal extracellular matrix. These studies may also have direct application to corneal cryopreservation, in general, and may lead to improved methods of storing tissues for lamellar and penetrating keratoplasty.
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