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Background: This study evaluates epithelialization, clarity, intraocular inflammation, and fibroblast ingrowth of a collagen corneal allograft derived from rabbit dermis., Methods: Dermal collagen fibers were dispersed intact and chemically modified to make them soluble. The allografts consisted of a fibrous, opaque peripheral zone and a central clear area. Twelve New Zealand white rabbits underwent penetrating keratoplasty with implantation of an allograft. The grafts were evaluated daily for clarify, anterior segment inflammation, and extent of reepithelialization with a slit-lamp microscope., Results: Epithelialization of the fibrous peripheral zone of the graft ranged from 0% to 90%. The central clear area did not epithelialize in any of the animals. Fibroblasts migrated into the peripheral zone in all eyes. Complications included ulceration of the central clear area in two eyes. There was no ulceration or leakage at the graft-host interface and no synechia, fibrous, or inflammatory retrocorneal membranes in any of the eyes., Conclusions: Our study is the first to describe the method of modifying dermal type I collagen into a clear corneal allograft. Survival of the corneal collagen allograft beyond 1 month may be limited by several factors including lack of epithelialization of the central clear area.

Background: Excimer laser photoablation effectively and precisely removes corneal tissue but may not smooth irregularities on the anterior corneal surface. An even surface might be obtained by applying a smoothing substance that fills in irregularities and ablates at the same rate as corneal tissue. Evaluation of collagen gel as a smoothing agent is reported., Methods: Pure, type I collagen solutions were prepared to remain soluble at physiological pH and to spontaneously gel when exposed to cationic buffers. Collagen gels were formed on the surface of enucleated porcine corneas and on human donor corneas and exposed to varying pulses of 193-nanometer excimer laser energy. Effects of collagen gel on ablation depth, corneal surface smoothness, and smoothing of roughened cornea were evaluated by examining scanning electron micrographs of control and treated specimens., Results: Collagen gels formed from 5 mg/ml collagen solutions dramatically altered the depth of photoablation. Photoablation of roughened cornea with collagen gels produced smooth corneal surfaces, whereas control eyes remained roughened and irregular. The smoothness of photoablated cornea surfaces improved when collagen gels were applied prior to photoablation., Conclusions: The rapidly gelling collagen solution appears to exhibit the functional properties required for an effective smoothing agent for excimer laser photoablation. The substance has low viscosity when applied to the corneal surface and forms a rigid gel when exposed to cationic buffer solution. In addition, the concentration of the collagen gel can be adjusted to provide different ablation rates.