First Insights Into The Corneal Tissue Compatibility Of A Novel UV Femtosecond Laser

Abstract

Purpose: : The major goal of this study was to histologically and cytologically characterize the corneal laser sections administered by a novel 345nm ultraviolet femtosecond laser (UV-FSL) developed by Alcon-WaveLight. Investigations were aimed at providing first insights into the tissue compatibility of the applied laser pulses.

Methods: : In a total of 6 enucleated porcine eyes, corneal flaps (depth: 200µm; diameter: 9.5mm) and lenticules (depth: 250µm; diameter: 6.5mm) were cut with a femtosecond laser. In 3 of those eyes, the intrastromal sections were administered by a novel 345nm UV-FSL with a pulse energy of 50nJ and a spot separation of 4x4µm. In the 3 remaining eyes, the laser sections were applied by an infrared femtosecond laser (IR-FSL) already in clinical use, with 0.52µJ pulse energy and 5x5µm spot separation. From the lasered corneas, specimens were excised, embedded sagittally in Epon and analyzed morphologically. In order to check for harmful impact of the UV-FSL on the endothelial cells, a circular plane (diameter: 8.5mm) was cut at a distance of 50µm from the endothelium in 6 enucleated rabbit eyes (90nJ, 3x3µm). Endothelial cell viability was assessed by trypan blue/alizarin red staining, Tunel assay and standard histological examination of semithin sections.

Results: : The reference IR-FSL sections were identified microscopically. No evident apoptotic or necrotic keratocytes were found in the periphery of the laser cuts. No accurate and distinguishable sectional plane could be found in the UV-FSL specimens. However, the region where the laser disrupted the stroma was demarcated by a conspicuous striation pattern perpendicular to the sectional plane, most probably representing the laser pulses. Electron microscopical examination revealed the striations as minute laser cuts. Necrotic cells were found in the area directly surrounding the region disrupted by the UV-FSL. There was no indication of impaired endothelial cell viability due to UV-FSL treatment. Morphologically, the endothelium had a healthy appearance and showed no evidence of apoptosis.

Conclusions: : Necrosis around UV-FSL cuts was very restricted in its spatial extension and the endothelium showed no signs of cellular impairment. Short-term corneal tissue compatibility of the novel UV-FSL is promising and encourages further investigations.

Keywords: laser • cornea: endothelium • refractive surgery: other technologies