'Orientation teeth' in non-mechanical laser corneal trephination for penetrating keratoplasty: 2.94 μm Er:YAG v 193 nm ArF excimer laser

Background/aims. 'Orientation teeth' at the donor trephination margin and correspondent 'notches' at the host margin facilitate graft orientation and avoid 'horizontal torsion' induced by asymmetric suture placement. In this study the quality and reproducibility of these structures created by non-mechanical laser corneal trephination were compared using two laser emissions. Methods. The procedure was performed in 20 enucleated pigs' eyes using open metal masks with eight 'orientation teeth/notches' (0.3 x 0.15 mm, base x height), an automated globe rotation device, and either a 193 nm ArF excimer laser or a Q switched 2.94 μm Er:YAG laser. 'Teeth/ notches' were analysed by planimetry and scanning electron microscopy (SEM). Results. Mean size was 0.30 (0.027) x 0.16 (0.017) mm for 'teeth' and 0.30 (0.035) x 0.15 (0.021) mm for 'notches' (excimer), and 0.31 (0.022) x 0.16 (0.015) mm and 0.30 (0.031) x 0.14 (0.021) mm respectively (Er:YAG). Overall, variability of notches was higher than that of teeth. By SEM, comparable cut regularity and sustained ablation profile were observed with both lasers. However, the corneal surface at the cut edge appeared slightly elevated (≤ 35 μm) in the Er:YAG group. Conclusion. Orientation teeth/notches resembling those obtained with the excimer laser can be created using the Q switched Er:YAG laser, with potential advantages of lower costs, convenient equipment size, and solid state safety.