Effect of radial keratotomy incision direction on wound depth

The majority of ophthalmic surgeons who perform radial keratotomy make incisions from the optical clear zone to the limbus (downhill; centrifugal), instead of from the limbus to the optical clear zone (uphill; centripetal). To compare the efficacy of these techniques, one surgeon performed keratotomy incisions in 10 eyes of 5 monkeys using the same double-edged diamond blade set to 80% of central pachometry. Four or eight centrifugal (downhill) and centripetal (uphill) incisions were made in each eye. Achieved incision depth was measured by light microscopy 2.5 to 8 months postoperative. Downhill incision depth averaged 46% (range 38% to 61%), whereas uphill incision depth averaged 74% (range 53% to 87%) (P less than .0005). In both groups, incision deviation from the perpendicular (lateral tilt error) was greatest adjacent to the optical clear zone (P less than .01). These differences may be explained by tilt error (forward or backward) or by the perpendicular front cutting action of a vertical blade being more effective than the angled blade.