LENS

in anatomy, a colourless, nearly transparent biconvex structure suspended behind the iris of the eye, the sole function of which is to focus light rays onto the retina. The lens is made up of unusual elongated cells that have no blood supply but obtain nutrients from the surrounding fluids, the aqueous humour in front and the vitreous behind. The shape of the lensessentially that of a flattened globecan be altered by the relaxation and contraction of the ciliary muscles surrounding it, thus enabling the eye to focus clearly on objects at widely varying distances. The ability of the lens to adjust from a distant to a near focus, called accommodation, gradually declines with age, often requiring correction. Clouding or opacity of the lens, called a cataract, may also occur with age and cannot be corrected except by surgical removal of the lens.