Accuracy of the microkeratome keratectomies in pig eyes

Keratokyphosis is a procedure of lamellar refractive corneal surgery in which corneal tissue does not have to be frozen. Corneal lamellae of 30 pig eyes were separated with either the Berlin microkeratome developed for keratokyphosis or the Barraquer microkeratome. The layer thickness was measured within the optical area at 25 measuring points 0.2-mm apart using the Universal Measuring Microscope. Corneal lamellae separated parallel to the surface by means of the Berlin microkeratome showed layer-thickness differences of 0.008 +/- 0.028 mm in the optical zone between the beginning and end of the incision. When using a convex applanation surface in the microkeratome with an optical zone of 5 mm and a vertex of 0.22, 0.2, and 0.15 mm, the vertex of the central part of the optical zone in the corneal disc attained a value of 0.114 +/- 0.018 mm instead of 0.114 mm (100%), 0.075 +/- 0.015 mm instead of 0.105 mm (72%), and 0.076 +/- 0.014 mm instead of 0.080 mm (84%) (mean +/- standard deviation [SD]). When using a concave applanation surface with the same vertex, it attained 0.076 +/- 0.020 mm (67%), 0.075 +/- 0.019 mm (72%), and 0.067 +/- 0.027 mm (84%). The measured vertex of the corneal lamellae was shifted up to 0.8 +/- 0.5 mm in the feed direction of the microkeratome, probably due to the frictional forces acting on the blade during the cutting process. After separation of the lamellae, the cut surface of the eye was measured planimetrically.(ABSTRACT TRUNCATED AT 250 WORDS)