Background: In penetrating keratoplasty, trephination with the 193 nm excimer laser may help avoid the differences in the deformation of the donor and recipient wound margins which occur with the conventional procedure. By varying the shape of the "open metal mask", other cut configurations can be achieved besides circular. Thus, "vertical tilt" and "horizontal torsion", both potential reasons for persistent long-term astigmatism after PK, may be minimized. Following experimental studies, the authors present the results obtained in their first 70 consecutive patients.
Patients and methods: 38 women and 32 men were treated (mean age 60.6 years, range 17 to 89 years). Indications were corneal processes without vascularization: Fuchs' dystrophy (n = 32), other stromal dystrophies (n = 5), secondary corneal endothelial decompensation (n = 6), keratoconus (n = 15), nonvascularized corneal scars (n = 4) and miscellaneous (n = 8 ). We used elliptical metal masks with/without orientation teeth and circular masks with four and eight orientation teeth, respectively. The HeNe aiming beam was manually controlled by a micromanipulator ("joystick"). The technical data of the laser were as follows: spot mode, 1.5 x 1.5 mm; repetition rate 30/sec and 25/sec, respectively; pulse energy 15-25 mJ; mean number of pulses 6407 (recipient) and 9150 (donor). With an elliptical outline, wound closure was usually achieved with single sutures. With a circular outline with orientation teeth, wound closure was most commonly achieved with a double running suture. Patients were prospectively documented using modified Erlangen record sheets. Follow-up ranged from 3 months to 3.4 years (mean 11.4 months).
Results: With two exceptions, penetration of the anterior chamber with the 193 nm excimer laser was accomplished without deformation of the cut edges. The elliptical outline facilitated fitting of the graft into the recipient wound bed, and the orientation teeth made fitting even easier. Initial intraoperative complications due to excessive laser energy densities included minor thermally induced corneal alterations caused by the heat of the metal mask and in a few cases minimal iris bleeding during corneal penetration. The median duration of re-epithelialization was two days. Wound healing was without complications. In particular, no primary graft insufficiency and no unexpected effects in donor or recipient corneas, iris, lens or posterior segments were observed. Postoperative complications were one corneal ulcer caused by premature fitting of an extended-wear contact lens and two immunologic graft reactions (3%). Mean astigmatism after suture removal was 4.6 D with an elliptical outline, and 3.9 D after trephination with orientation teeth and with the sutures in situ.
Conclusion: Non-mechanical, "non-thermal" trephination with elliptical and circular metal masks with orientation teeth represents a viable alternative to knife trephination in penetrating keratoplasty. No unexpected complications such as disturbances of wound healing were seen. Further studies are needed to determine the effect on residual long-term astigmatism after suture removal.