Q-switched CTE:YAG laser sclerostomies on human autopsy eyes

Experimental laser sclerostomies were performed on human eye-bank eyes with a new mid-infrared solid-state laser that is characterized by adequate optic-fiber transmission and low-thermal tissue interaction. The laser presented herein works with a chromium thulium erbium-doped (CTE): YAG crystal as the active medium, emitting radiation at a wavelength of 2.69 microns. In the Q-switch mode, the pulse duration is tunable from 0.5 to 2.5 microseconds. The maximal energy is 50 mJ/pulse (1-10 Hz). Attenuation of energy transmission in quartz (0.3 ppm) optic fibers is < 8 dB/m (diameter, 200 microns). Absorption depths of 2.69 microns radiation in water is 12.5 microns. In vitro procedures performed were ab-interno and ab-externo full-thickness sclerostomies. Histological and micro-morphological examination was performed by light microscopy and scanning electron microscopy. Collateral tissue damage in processed sclerostomies did not exceed 50(+/- 10) microns at typical fluences (10 J/cm2). In contact guidance, 10-15 laser pulses were required in the full-thickness ab-externo procedure, whereas up to 50 pulses were required in the ab-interno procedure. The number of laser pulses applied corresponded to the length of the filtration canals created. The canal was significantly longer (2.5 +/- 1 mm) in the ab-interno approach than in the ab-externo approach (1 +/- 0.2 mm). The intraocular ostium of the filtration canal in the ab-externo procedure showed enhanced signs of mechanical deterioration. It is concluded that both the wavelength (2.69 microns) and the pulse duration (0.5-2.5 microseconds) of the CTE: YAG laser are appropriate for laser sclerostomy.(ABSTRACT TRUNCATED AT 250 WORDS)