| 简介 |
A lens system comprising a biconvex lens element and a housing in which the biconvex lens element is mounted. The 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. The biconvex lens element comprises front and rear surfaces and 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. The lens system is configured such that the optical power of the lens element is between about 10 and about 40 diopters. |
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