| Unintended anterior corneal flattening is a poorly understood complication of excimer laser phototherapeutic keratectomy (PTX) that pervades clinical practice despite efforts to remove a geometrically neutral lenticule of tissue during ablation. This document describes investigations into a model of keratectomy-induced curvature change in which intraoperative thickening of the stroma peripheral to the ablation zone is implicated as a mechanical stimulus for flattening of the central cornea. A paired-control human donor eye study was conducted to assess the efficacy of preoperative topical glutaraldehyde (GTA) treatment as a technique for inhibiting PTK-induced peripheral stromal thickening and, secondarily, for attenuating the acute corneal flattening response.; Twenty whole globes acquired in same-donor pairs were individually mounted in a custom holder, inflated to normal intraocular pressure (15 mmHg) and deepithelialized. According to a crosslinking protocol developed in preliminary experiments, one cornea of a given donor pair was immersed in a 15% dextran solution for 40 minutes then transferred to 4% GTA/dextran for an additional 20 minutes; the fellow control was exposed to 15% dextran for 60 minutes. Each eye was subsequently subjected to (1) sham PTK, a same-eye control phase incorporated to account for thinning due to intraoperative dehydration, (2) PTK(5-mm-diameter, 100-um-depth) and (3) a 1-hour hypo-osmotic soak phase designed to assess the anti-swelling activity of stromal crosslinking. A scanning-slit topography system was used to acquire triplicate thickness and curvature measurements before and after each experimental phase.; Crosslinking significantly inhibited peripheral stromal thickening during PTK and postoperative hypo-osmotic immersion. In addition, during PTK, crosslinked corneas demonstrated 36% less hyperopic shift relative to paired controls (p =.001). The magnitude of this latter effect was linearly dependent upon the magnitude of crosslink-mediated suppression of the peripheral thickening response to PTK (r = 0.68, p =.03). The results demonstrate that acute hyperopic shifts in a donor model of PTK can be significantly reduced through preoperative application of a collagen crosslinking reagent and therefore support the conclusion that mechanical events in the corneal periphery play an important role in keratectomy-induced central cunrature changes. This mechanism of curvature change is not accounted for in current surgical algorithms. |
