Ablation of vitreous tissue with erbium : YAG laser

PURPOSE. Using a noncontact erbium (Er):yttrium-aluminium-garnet (YAG) lase r, ablation of vitreous was compared to distilled water in vitro. METHODS. The porcine vitreous body and distilled water were ablated in vitr o at different pulse lengths and pulse energies. Selected pulse energies we re 25, 35, 45, 75, and 100 mJ (pulse rate: 1 Hz; laser beam diameter at the surface of the sample: 2 nlm). Pulse lengths were at 140 +/- 3 mu sec, 190 +/- 4 mu sec, and 240 +/- 5 mu sec. The loss of weight in vitreous tissue and distilled water was measured using precision scales and corrected for e vaporation, respectively. The Mann-Whitney U test was used to assess the si gnificance of differences in ablation rates of water and vitreous. P < 0.05 was considered statistically significant. RESULTS. Reproducible and constant ablation rates were found in both vitreo us and distilled water in each of 10 consecutive series of 50 laser pulses at constant laser parameters. Ablation rates per pulse (mu g/mu sec) of vit reous tissue were as follows: 3.0 mu g to 45.8 mu g (140 mu sec), 10.4 mu g to 53.8 mu g (190 mu sec), and 17.9 mu g to 24.2 mu g (240 mu sec). The ab lation rates exhibited a linear correlation with increasing pulse energies and also with decreasing pulse lengths. Considering the pulse lengths of 19 0 mu sec and 240 mu sec with all pulse energies tested, the ablation rates of distilled water were significantly higher (P < 0.05) than ablation of vi treous tissue. The ablation rates at a pulse length of 140 mu sec were not significantly different. The differences per pulse were as follows. 0.5 mu g to 2.1 mu g (140 mu sec), 1.9 mu g to 6.0 mu g (190 mu sec), and 3.5 mu g to 8.7 mu g (240 mu sec). CONCLUSIONS. Vitreous ablation is possible using Er:YAG laser. The ablation characteristics of vitreous have proved to be similar but not equal to tha t of water.