Dye-targeted non-contact diode laser photothermal keratoplasty for correction of hyperopia

Purpose. Parel et al. (1994) have described non-contact laser photothermal keratoplasty using a slit lamp-coupled pulsed Holmium:YAG laser. In addition, Wapner et al. (1992) have described dye-enhanced diode laser thermokeratoplasty as yet another means of corneal refractive control. Here we present a laboratory model combining these 2 modalities. Methods. A slit lamp-mounted 810 nm diode laser (Iris Medical) was used to thermally shrink areas of de-epithelialized human cadaveric corneas (4 eyes 2 days post-mortem, 5 eyes 6 days post-mortem, intraocular pressure 20-25 mm Hg) targeted with topical saturated indocyanine green dye. Laser energy (750 mW, 500 micron, 500 msec, 2 shots) was applied to 6 symmetric dye-marked spots in a 6 mm diameter optical zone to effect central steepening. Immediately after thermal refraction the globes were examined with a vertically-mounted corneal topographic analysis system (EyeSys Technologies) or by manual keratometry (Bausch & Lomb). Results. Hyperopia correction was indeed observed consistent with the results of Parel et al. (1994) using the Holmium: YAG laser. For the 2 day-old globes, the achieved correction was 6.9±0.6D, and for the 6 day-old globes 9.2±1.1D. Conclusion. Dye-targeted non-contact diode laser photothermal keratoplasty is a valid laboratory technique. The main advantage of this modality is that the dye target allows for more precise application of laser energy. In addition, 810 nm diode laser light has minimal effects on unstained cornea. The error in this study was approximately 10%. The corrections achieved depended on post-enucleation age, perhaps due to differences such as corneal hydration. In vivo studies are planned.