About 9mm in diameter and 4 mm thick, the crystalline lens provides perhaps 20% of the refracting power of the eye. Hecht likens it to a tiny transparent onion with some 22,000 fine layers. The index ranges from about 1.406 at the center to about 1.386 in outer layers, making it a gradient index lens. It is pliable, and changes shape to accomplish accommodation for close focusing.
About 9mm in diameter and 4 mm thick, the crystalline lens provides perhaps 20% of the refracting power of the eye. Hecht likens it to a tiny transparent onion with some 22,000 fine layers. The index ranges from about 1.406 at the center to about 1.386 in outer layers, making it a gradient index lens. It is pliable, and changes shape to accomplish accommodation for close focusing.