RAPIDLY POLYMERIZED COLLAGEN GEL AS A SMOOTHING AGENT IN EXCIMER-LASER PHOTOABLATION

BACKGROUND: Excimer laser photoablation effectively and precisely remo ves corneal tissue but may not smooth irregularities on the anterior c orneal surface, An even surface might be obtained by applying a smooth ing substance that fills in irregularities and ablates at the same rat e as corneal tissue, Evaluation of collagen gel as a smoothing agent i s reported, METHODS: Pure, type I collagen solutions were prepared to remain soluble at physiological pH and to spontaneously gel when expos ed to cationic buffers, Collagen gels were formed on the surface of en ucleated porcine corneas and on human donor corneas and exposed to var ying pulses of 193-nanometer excimer laser energy, Effects of collagen gel on ablation depth, corneal surface smoothness, and smoothing of r oughened cornea were evaluated by examining scanning electron microgra phs of control and treated specimens, RESULTS: Collagen gels formed fr om 5 mg/ml collagen solutions dramatically altered the depth of photoa blation. 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 whe n collagen gels were applied prior to photoablation, CONCLUSIONS: The rapidly gelling collagen solution appears to exhibit the functional pr operties required for an effective smoothing agent for excimer laser p hotoablation, The substance has low viscosity when applied to the corn eal surface and forms a rigid gel when exposed to cationic buffer solu tion, In addition, the concentration of the collagen gel can be adjust ed to provide different ablation rates.