Accuracy of corneal lenticules produced for lamellar refractive corneal surgery

The layer thickness of the corneal lenticules separated with the Berlin microkeratome and shaped by keratomileusis, keratophakia, keratokyphosis, and intrastromal excimer-laserkeratomileusis was measured with the Universal Measuring Microscope. The vertices of most corneal lenticules showed an undercorrection of the measured values compared with the calculated ones. In keratomileusis, the vertex of the central part of the optical zone of 3.6 mm attained 79 +/- 19 microns instead of 80 microns (99%); in keratophakia, 74 +/- 19 microns instead of 80 microns (93%); in myopic keratokyphosis, 77 +/- 11 microns instead of 105 microns (74%); in hyperopic keratokyphosis, 72 +/- 28 microns instead of 105 microns (69%); and in excimer-laserkeratomileusis, 52 +/- 12 microns instead of 39 microns (120%). The undercorrection of myopic and hyperopic keratokyphosis indicate that this type of nonfreeze keratomileusis is not capable to cut a tissue lens of predicted refraction from compressed corneal tissue. Near symmetrical profiles were achieved in all types of refractive corneal surgery but excimer-laserkeratomileusis had the smallest standard deviation. It was significantly smaller than in hyperopic keratokyphosis (p < 0.05). Intrastromal excimer-laserkeratomileusis of tightly fixed corneal lenticule in the Berlin microkeratome might be the most predictable method of lamellar refractive corneal surgery.