THE REGULARITY OF LASER KERATECTOMY DEPTH IN NONMECHANICAL TREPHINATION FOR PENETRATING KERATOPLASTY

BACKGROUND AND OBJECTIVES: To study the regularity of laser keratectom y depth in nonmechanical trephination for penetrating keratoplasty (PK ) and to assess its implications on astigmatism and visual acuity (VA) . PATIENTS AND METHODS: In this retrospective clinicopathologic study, the authors enrolled 26 women and 32 men (mean age 54 +/- 20 years) w ith either keratoconus (n = 27) or Fuchs' dystrophy (n = 31), who unde rwent excimer laser (193 nm) trephination using a manually guided beam . Donor cornea trephination was performed using an artificial anterior chamber and either an automated rotation device (n = 27) or a manuall y guided beam (n = 31). The minimum residual corneal thickness (MRCT) and the random residual corneal thickness (RRCT), requiring division w ith scissors in excised patient buttons or corneoscleral donor rims, w ere assessed in a masked fashion using histologic sections. The postke ratoplasty keratometric net astigmatism, the subjective cylinder, and the VA were evaluated before and after suture removal. RESULTS: In pat ients with keratoconus, the mean MRCT (13% +/- 14%) and RRCT (38% +/- 20%) were significantly higher than in the patients with Fuchs' dystro phy (7% +/- 11% and 26% +/- 15%, respectively) (p < .01). When an auto mated rotation device for trephination of the donor cornea was used, t he mean MRCT (2% +/- 4%) and RRCT (14% +/- 11%) were significantly sma ller than when a manually guided laser beam was employed (15% +/- 12% and 38% +/- 15%, respectively) (P < .001). After suture removal, the V A increased significantly with automated trephination (P = .04), but n ot with manually guided trephination of the donor cornea (P = .24). Ho wever, after a mean follow-up of 30 +/- 8 months, the differences in t he mean keratometric astigmatism, refractive cylinder, and VA after au tomated trephination (3.0 D, 2.6 D, 20/29, respectively) compared with those after manually guided trephination of the donor cornea (4.3 D, 3.3 D, 20/33, respectively) did not reach statistical significance. CO NCLUSIONS: The regularity of donor trephination depth can be significa ntly improved by using an automated rotation device instead of a manua lly guided beam. Although residual postkeratoplasty astigmatism was no t directly related to trephination depth, the improvement of the funct ional results after suture removal seems to be promoted by automated t rephination.