Holmium laser thermokeratoplasty.

Abstract

Corneal curvature can be altered by shrinking stromal collagen with a pulsed solid-state holmium: YAG laser in a procedure termed laser thermokeratoplasty. The authors performed laser thermokeratoplasty in 40 human cadaver eyes using a ring pattern of 32 spots, each spot having a diameter of 300 microns. The amount of induced corneal steepening decreased as ring diameter was increased in 1 mm increments, with 22.2 +/- 3.3 and 3.7 +/- 2.0 diopters (D) of central steepening with diameters of 3 and 7 mm, respectively. Results of histologic examination showed a cone-shaped zone of increased stromal hematoxylin uptake extending posteriorly for 90% of stromal thickness. Energy levels greater than those needed to induce topographic changes produced limited endothelial injury in rabbit corneas and, in some cases, intraocular inflammation. A computerized, finite element model of the globe demonstrated central corneal steepening as a result of heat-induced stromal contraction to a depth of 75% corneal thickness. These data support previous studies indicating that central corneal topography can be modified by heating corneal stroma in a controlled fashion with the mid-infrared holmium:YAG laser.