COMPARISON OF THE STANDARD COMBINED (BIDIRECTIONAL) RADIAL KERATOTOMYTECHNIQUE WITH THE UNDERCUT TECHNIQUE IN HUMAN DONOR EYES

BACKGROUND: We evaluated the efficacy of a new radial keratotomy techn ique, using a diamond designed to undermine the central clear zone wit hout incising superficial stroma. METHODS: An 8-incision radial kerato tomy at a 3-mm central clear zone was performed on nine pairs of human donor globes. One eye of each pair was incised using the standard com bined (bidirectional) technique diamond and the contralateral eye, usi ng the undercut bidirectional technique diamond. Paired t-tests were u sed to compare changes in central corneal curvature between these two groups. Microscopic analysis of incision morphology was performed on f our eyes. RESULTS: Corneal topography at the 1-, 3-, and 5-mm annular zones revealed corneal flattening of 7.70 +/- 1.50 diopters (D), 6.70 +/- 1.30 D, and 5.10 +/- 1.00 D, respectively, in the undercut bidirec tional technique group versus 6.20 +/- 1.70 D, 5.30 +/- 1.50 D, and 4. 00 +/- 1.20 D, respectively, in the standard bidirectional technique g roup (P <0.01 for each annular zone). Light microscopy (serial section s) revealed an average incision depth of 80.9 +/- 3.9% in the undercut bidirectional technique group versus 72.7 +/- 4.5% in the combined gr oup (P <0.01). The undercut bidirectional technique incisions undermin ed the central clear zone for a distance of approximately 350 mu m com pared to about 140 mu m for the standard bidirectional incisions. CONC LUSIONS: In the human cadaver eye, the undercut technique of radial ke ratotomy provided greater flattening than the standard bidirectional t echnique. The greater amount of flattening may result from greater cen tral extension of the undercut incisions beneath the central clear zon e, from greater incision depth, or from a combination of both factors.