Lens for indirect ophthalmoscopy

Abstract

A lens for use in indirect ophthalmoscopy having two functions; firstly as a condensing lens converging light from an ophthalmoscope light source to the pupil of the eye and thereby illuminating the fundus of the eye, and secondly and simultaneously as an image forming lens which forms an aerial image of the fundus of the eye, which image is viewed monocularly with a monocular indirect ophthalmoscope or binocularly and stereoscopically with a binocular indirect ophthalmoscope. The novel features of the lens of this invention are that both the front and back surfaces of the lens are positive aspheric surfaces of revolution of conoid type on a common axis of revolution, the dioptric power at the apex of the front surface of the lens being approximately twice that of the apex of back surface of the lens, which back surface faces the eye being examined, the eccentricity of the front surface bearing a definite relationship to the eccentricity of the back surface, the eccentricities of the two surfaces of the lens being a function of the sum of the dioptric powers of the two surfaces of the lens, the eccentricities and apical dioptric powers of the surfaces of the lens being such that the lens converges the light from the ophthalmoscope light source to a precise image of the source at the entrance pupil of the eye, and simultaneously the lens forms with the light emerging from the eye a substantially flat aerial image of the fundus of the eye in which images the aberrations of the image including curvature, astigmatism and distortion are optimally corrected.