[Experimental studies on the effect of the Er:glass and Cr:Tm:Ho:YAG laser in thermokeratoplasty].

So far the dose-effect ratio of the Holmium laser (wavelength 2.12 microns) and the erbium laser (1.54 microns) for laser thermokeratoplasty (LTK) are not defined in detail. Our study was designed not only to compare the erbium contact and the holmium non-contact applications but also to throw light on the influence of different geometrical application patterns, pulse energies, pulses per coagulation site and repetition rates under experimental conditions. Enucleated sheep and pig eyes were used 2-6 h post mortem, pressurized to 25 mmHg and moisturized with saline solution. Before and after LTK, pachymetry and keratometry were performed. Some specimens were prepared for light and scanning microscopy. The coagulation threshold for the erbium laser in a contact mode with a 200-microns fibre was 25 J/cm2 (ca. 8 mJ/pulse) and for the holmium laser 8 J/cm2 (ca. 2.5 mJ/pulse). The erbium laser was used in a single shot per spot mode, the holmium laser in repeated pulse per spot mode. With the single shot per spot mode, we were able to induce a promising hyperopic shift of up to -3.47 +/- 0.61 D, while myopic changes could only be induced up to +1.89 +/- 0.74 D. Higher changes of up to +8.27 +/- 1.3 D could be achieved by means of repeated pulses per spot (20 pulses, 45 mJ, 10 Hz). Our experiments showed an obvious increase of dioptric changes when using a higher repetition rate while pulse energy and number were kept constant.(ABSTRACT TRUNCATED AT 250 WORDS)