Corneal wound healing after photoablation with a 213-nm scanning solid state laser: histological and ultrastructural study

To investigate wound healing in rabbits after corneal photoablation with a 213 nm UV scanning solid state laser. We used a frequency quintupled Nd:YAG laser to photoablate the cornea of 32 rabbits (5 mm ablation zone, 6 D myopic correction). The contralateral eyes and the eyes of 3 untreated animals served as controls. Light and electron microscopy analyses were performed on postoperative days 0, 7, 28, 90. Abnormal, light basal epithelial cells were observed during the first postoperative month, but normal epithelial maturation was evident at 3 months. Basement membrane duplication was noted. Keratocyte proliferation occurred in the anterior stroma and in a few cases, in the posterior stroma, where keratocyte activation was present. Degenerative endothelial changes were observed immediately after ablation with intracellular disorganization and junction alteration. Surface profiles with variable regularity led to a variable wound healing. Apart from differences in epithelial basal cell appearance, photoablation with a 213 nm solid state laser induced wound healing processes similar to those observed previously with prototype ArF excimer lasers. It is hoped that laser refinements will improve the surface regularity and lead to more consistent wound healing responses. However, several studies are required to assess mutagenicity, penetration depth and ablation rate of the 213 nm wavelength on ocular tissues, as well as the effects of hydration on the clinical outcome

<title>Corneal photoablation with a scanning beam of 213 nm radiation for alteration of refraction: a three-month follow up study of the rabbit</title>

A scanning pulsed beam at 213 nm creates predictable correction of myopia but the surgical procedure with the presently used laser system is not yet sufficiently safe to proceed to human clinical trials. It was found that a 70% overlap of approximate active spot size provides a refractive change as predicted 1 week after ablation. There was a minimal transient increase of IOP shortly after the ablation. There was an immediate swelling of the cornea after the ablation that gradually decreased during the following 12 weeks. The corneal epithelium did not heal until around 4 - 7 weeks after the ablation. The epithelium stained with fluorescein late after the ablation. When considerable haze was seen it decreased towards the end of the 12 weeks of observation. Approximately 30% of ablated corneas showed vessel ingrowth at 12 weeks after ablation. The 213 nm beam was obtained by frequency quintupling of the output of a Nd-Yag laser. The beam was moved with an X-Y scanner

Three month follow-up of changes in the rabbit cornea after photoablation with a pulsed scanning beam at 213 nm

A scanning beam of nano-second pulses at 213 nm flattens the cornea as predicted. However, there is a considerable variability in the flattening and the ablation is not safe. Ablation for 16 D flattening with an active spot overlap of 50% induced 8.9 +/- 5.3 D (n equals 7) as measured by the TMS topography system (ring 7 average) and 5.8 +/- 4.1 D (n equals 5) as measured with the SK-1 (2 mm zone) system. Ablation for 6 D flattening with an active spot overlap of 70% induced approximately 2 D flattening to 2 D steepening (n equals 3) as measured with the TMS (ring 7) and 6.6 +/- 4.33 D (n equals 7) flattening as measured by SK-1 (2 mm zone) keratometry. There was no change in IOP at 12 weeks after as compared to before ablation. There was a net increase of central and peripheral corneal thickness at 12 weeks after the ablation as compared to preoperatively. Epithelial defects remained up to 4 weeks after ablation. After four weeks, vessels had invaded the cornea in 30% of the cases and remained throughout the three months observed. It is concluded that 213 nm nano-second pulses can be used for flattening the cornea but the system should not be used for clinical trials in humans until the adverse effects can be avoided