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