Abstract: An ophthalmic endothelial microscope assembly capable of determining a predetermined dimension, namely the thickness, of the cornea portion of an eye of a living patient. The present assembly includes a casing having an illumination directing means including a plurality of optical elements disposed between an illumination source and an objective lens. Sighting means, also optically aligned with the illumination directing assembly, is further optically aligned with the objective lens so as to attain proper sighting of the predetermined portion of the eye. A focusing assembly includes a plurality of linkage elements drivingly interconnected to both a gauge member and the objective lens whereby manipulation of the focusing assembly causes proper positioning and focusing of the objective lens relative to the cornea of the eye under examination concurrently to activation of the gauge member so as to determine accurately the actual thickness or other predetermined dimension of the cornea.