US Patent 7499219 Optimized lens for indirect ophthalmoscopy

An autoclavable diagnostic ophthalmic lens system includes a biconvex lens element having front and rear surfaces and a housing in which the biconvex lens element is mounted. The biconvex lens element is fabricated from a glass having an index-of-refraction greater of 1.7 or greater. The glass composition meets the following parameters:(% SiO2 (by weight)+% B2O3) is less than 50%;% of alkali metal compounds+% of alkaline earth metal compounds is less than 10%; and(% SiO2+% B2O3)/(% rare earth compounds) is less than 1.