Wavelength Optimisation In Femtosecond Laser Corneal Surgery: Quantitative Results On Eye Bank Corneas

Abstract

Purpose: : In former studies we have argued that a wavelength change may considerably improves the outcome of femtosecond laser keratoplasty. The purpose of the present work is to quantify the penetration depth and investigate the incision quality as a function of the laser wavelength when performing laser keratoplasty.

Methods: : In this study 100 penetrating incisions and 10 lamellar incisions have been performed on human corneas using wavelengths of 1.03 µm (which is typical for clinical systems) and the wavelengths in the range of 1.4-1.7 µm, where 1.65 µm corresponds to the wavelength which had been identified as optimal during previous studies.The pulse characteristics were pulse duration of 700 femtoseconds, repetition rates of 1-10 kHz and energies in the range of 0.5-2 µJ. The laser pulses were focussed using different microscope objectives with numerical apertures ranging from 0.3 to 0.6.During the experiments, the corneas were fixed on an artificial chamber mounted on stepmotors allowing for three-dimensional positioning with micrometric precision with respect to the position of the laser beam focus.The incisions were subsequently analysed using scanning and transmission electron microscopy (SEM and TEM, respectively).

Results: : Confirming previous studies, we obtain an optimal penetration depth when the cornea is treated using a laser wavelength of 1.65 µm. Using this wavelength, the observed incision quality of lamellar interface is at least conserved compared to the quality obtained when performing lamellar cut at 1.03 µm; corneal flaps are more easily detached and wider pulse spacing is possible. The penetration depth is improved by a factor of at least 2 and up to 5; penetrating keratoplasty is possible even on strongly oedematous corneas.

Conclusions: : A wavelength change from 1.03 µm to 1.65 µm strongly improves the penetration depth while maintaining good incision quality in keratoplasty on healthy and strongly pathological corneas.

Keywords: cornea: basic science • laser