A variable focus telescopic instrument for indirect ophthalmoscopy with increased magnification and stereopsis

We devised a new binocular indirect ophthalmoscope and a complimentary examination technique that provide enhanced fundus magnification and optimum stereopsis through a wide range of patient pupillary apertures. The lightweight, mechanically simple instrument uses a variable focus Galilean telescopic observation system to enlarge the condensing lens image of the fundus seen by the examiner. The present device is capable of about X 1.5 fundus magnification with negligible stereopsis through a 20-mm patient pupil, continuously increasing to X 8.5 with greatly enhanced stereopsis through an 8-mm pupil. A zoom focusing capability considerably extends the magnification, stereopsis, and small pupip penetrating characteristics of a given condensing lens by allowing the examiner to binocularly observe the telescopically magnified fundus image throughout the 30-cm to 60-cm focusing range of the ophthalmoscope.