crystalline lens

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The biconvex, transparent, elastic structure immediately behind the iris of the vertebrate eye that helps to focus light rays on to the retina, although most (about two-thirds) of the refraction of light entering the eye occurs at the cornea. The degree of convexity of the crystalline lens can be altered by radial ciliary muscles up to about age 45, after which the lens becomes hard and its focus cannot be altered. See also aberration (3), accommodation (1), ametropia, aphakia, astigmatism, cataract, cycloplegia, lens, refraction. Compare compound eye, ommatidium. [So called because of its internal crystalline structure]

Subjects: Psychology.

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