Lamellar excimer laser keratoplasty: reproducible photoablation of corneal tissue. A laboratory study.

We examined the depth of ablation of the recipient bed with different counts of oscillations of excimer laser beam, to determine the correlation between planned and real depth. The ablation rate per oscillation was tested preoperatively by blackened photographic paper of defined thickness and thus was calculated to be 5 microns. Forty pig eyes were used for the first study. Each eight eyes were ablated in the planned depth 100 microns, 200 microns, 300 microns, 400 microns and 500 microns. The corneal thickness was measured with an ultrasonic pachymeter before and after the procedure. The depth measured after the photoablation was 99.4 +/- 36.4 microns for 100 microns planned depth, 186.7 +/- 55.3 microns for 200 microns, 298.4 +/- 68.5 microns for 300 microns, 373.9 +/- 65.7 microns for 400 microns and 480.1 +/- 59.3 microns for 500 microns. Comparing the depth measured after the photoablation to planned depth, there was a significant correlation (correlation coefficient: R = 0.93; p < 0.0001). Five other corneas trephinated from pig cadaver eyes were ablated from the endothelial side to the desired thickness (100 to 500 microns) of lamellar graft. In a second step a donor mask was placed onto the cornea and a laser light spot was led until perforating on all sides. The lamellar keratoplasty was completed by suturing the corneal graft into the bed. Macroscopic and microscopic examination of sutured eyes after fixation showed a good fit of wound margins and stromal interface. These results indicate that excimer laser is useful for reproducible corneal photoablation in lamellar keratoplasty.