Abstract: A high resolution contact lens structure increases the numerical aperture of a long working distance microscope, while correcting the chromatic and spherical aberrations generated at the surface between the lens structure and the cornea. The structure in one embodiment has a front plate element having two parallel flat lens surfaces. A first lens element has a flat first lens surface in contact with the plate, and a concave second surface. A second lens element has a convex first lens surface in contact with the concave second surface of the first lens element, and a convex second lens surface. The lens element thicknesses, lens surface radii and indices of dispersion and refraction of the lenses are selected to increase the numerical aperture of the microscope.

Abstract: A compact ophthalmic instrument for refraction of patient's eyes is obtained by substantial folding of the optical system. The optical system is folded in one location using a reflection means that moves to vary the location of a target image being viewed by a patient for identifying the spherical power of a corrective lens, if any, required by the patient. A second folded portion of the optical system contains a cylinder means for cylindrically varying the target image.