Measurement of the anisotropic thermal conductivity of the porcine cornea.

Accurate thermal models for the cornea of the eye support the development of thermal techniques for reshaping the cornea and other scientific purposes. Heat transfer in the cornea must be quantified accurately so that a thermal treatment does not destroy the endothelial layer, which cannot regenerate, and yet is responsible for maintaining corneal transparency. We developed a custom apparatus to measure the thermal conductivity of ex vivo porcine corneas perpendicular to the surface and applied a commercial apparatus to measure thermal conductivity parallel to the surface. We found that corneal thermal conductivity is 14% anisotropic at the normal state of corneal hydration. Small numbers of ex vivo feline and human corneas had a thermal conductivity perpendicular to the surface that was indistinguishable from the porcine corneas. Aqueous humor from ex vivo porcine, feline, and human eyes had a thermal conductivity nearly equal to that of water. Including the anisotropy of corneal thermal conductivity will improve the predictive power of thermal models of the eye.

Theory,equipment configuration and key techniques of LTK / 医疗卫生装备

Attention is being paid to the treatment of hyperopia(presbyopia) with laser thermokeratoplasty.This article mainly presents the theory of laser thermokeratoplasty(LTK),equipment configuration and some key techniques in laser delivery system.

The Effect of Holmium:YAG Laser Thermokeratoplasty on Corneal Astigmatism in Rabbits

This animal study was conducted to investigate the effect of holmium:YAG laser thermokeratoplasty on correction of hyperopic astigmatism. A pulsed holmium:YAG laser emitting a wavelength of 2.06 micrometer was used. Arcuate, reverse arcuate, linear patterns of laser burn were applied along the flat corneal meridian and their effects on the rabbit corneal curvature were studied. Keratometric measurements and cycloplegic refractive error were determined preoperatively, one, two, and three months after operation. The changes of refractive astigmatism in three patterns of laser burn were 0.8130, 3.0243, 0.8437 diopter, respectively, compared to that of the control group on postoperative three months. The changes of keratometric astigmatism were 1.1719, 3.0737, 0.7812 diopter, respectively, compared to that of the control group on postoperative three months. We found that holmium:YAG laser thermokeratoplasty is effective in steepening flat corneal meridian, and the most effective pattern is reverse arcuate type. In future holmium:YAG laser thermokeratoplasty might be clinically applicable as a operation of hyperopic astigmatism correction.