EXPERIMENTAL 193-NM EXCIMER-LASER TREPHINATION WITH DIVERGENT CUT ANGLES IN PENETRATING KERATOPLASTY

Purpose. To study the morphologic properties of divergent cut. angles after nonmechanical trephination for penetrating keratoplasty in donor s and recipients and to assess its implications for donor-recipient st ability in an experimental porcine model. Methods. An excimer laser 19 3-nm corneal trephination was performed in 30 enucleated porcine eyes by using a modified ''open mask'' (stainless steel sheet 10CrNi18), to obtain round donor buttons and corresponding recipient beds 7 mm in d iameter at the level of Bowman's layer. An automated globe-rotation de vice allowed different cut angles toward the optical axis. Three cut a ngles were intended: 0 degrees, 15 degrees divergent, and 35 degrees d ivergent, Quality of the cuts was assessed by means of hislology and s canning electron microscopy (SEM).In a different setting, after alignm ent of the donor button and corresponding recipient bed in an artifici al anterior chamber, intracameral pressure was increased stepwise, mod ifying the height of a bottle of balanced saline solution connected to the chamber. Criterion for ''instability'' was the movement of the do nor button in all four quadrants during observation with a surgical mi croscope (x12). Results. Reproducible cut angles and smooth cut surfac es of donors and recipients were confirmed by histologic and SEM evalu ation. Macroscopically, a good alignment of a divergent donor button i n a corresponding recipient bed was achieved. Instability of the donor buttons occurred with a water column niveau at 2 cm in the 0 degrees cut, at 3 cm in 15 degrees divergent cuts, and at 4.5 cm in 35 degrees divergent cuts. Coraclusion, The stability of a corneal donor button in a recipient bed seems to increase in proportion with the degree of divergence of the trephination angle. Considering the good histologic quality and macroscopic alignment obtained. divergent cut angles may a llow a reduction of sutures, assuring a water-light wound closure in p enetrating keratoplasty.