Patent ID: 7499219

Claim:
A lens system comprising a biconvex lens element and a housing in which said biconvex lens element is mounted, wherein: said biconvex lens element comprises front and rear surfaces; said front surface of said biconvex lens element comprises a radius of curvature of 125 mm or said rear surface of said biconvex lens element comprises a radius of curvature of 80 mm; said biconvex lens element comprises a diameter between about 0.5 inches to about 3.0 inches; said biconvex lens element is fabricated from a glass composition having an index-of-refraction of about 1.7 or greater; said glass composition comprises SiO 2 and B 2 O 3 ; a combined weight % of SiO 2 and B 2 O 3 in said glass composition is less than 50%; a combined weight % of alkali metal compounds and alkaline earth metal compounds in said glass composition is less than 10%; a ratio of said combined weight % of SiO 2 and B 2 O 3 over a weight % of rare earth compounds in said glass composition is less than 1; said biconvex lens element is configured to display an inverted and magnified indirect image of a retinal surface of an eye of a patient in a region external to the eye; and said lens system is configured such that the optical power of said lens element is between about 10 and about 40 diopters.