Investigations on laser thermokeratoplasty

Laser thermokeratoplasty (LTK) is a minimally invasive treatment to correct hyperopia and astigmatism. The increase in refractive power is achieved by thermally induced shrinkage of collagen in the corneal periphery. The authors used a flashlamp pumped holmium laser (λ = 2.12 μm) in combination with a non-contact focusing device to investigate the influence of laser pulse energy and repetition rate on the refractive outcome working with enucleated porcine eyes. The energy range useful for LTK was evaluated and a significant correlation between the refractive change and the pulse repetition frequency was found. To interpret these findings, the authors performed calculations of the spatial and temporal temperature profiles in the irradiated volume. The results suggest that the high peak temperatures occurring in pulsed LTK are less responsible for a contractive effect than the average temperature rise during exposure: Based on these results, the authors propose the use of cw-laser diodes emitting in the 2-μm spectral range for LTK.