Abstract: An apparatus for calibrating the blade extension of a microkeratome includes a magnifying device and a fixture for holding the microkeratome assembly adjacent thereto. The magnifying device defines a line of sight and includes a reticle visible in the line of sight. The fixture supports the bottom surface of the shim of the microkeratome in a plane parallel to the line of sight of the magnifying device. In measuring the blade extension, the reticle is first aligned with either the cutting edge of the blade or the bottom surface of the gauge member. Relative movement between the reticle and the fixture is effected until the reticle is aligned with the other of the cutting edge and bottom surface of the gauge member. A measuring device monitors the relative movement. The reading of the measuring device equals the blade extension of the microkeratome.