THE OPTICS OF THE EYE-LENS AND LENTICULAR SENESCENCE - A REVIEW

Although the lens of the eye is structurally a biological tissue, it f unctions as an optical element providing one third of the refracting p ower of the human eye, and a variable focus in younger years. Througho ut a life-time the optical properties of the eye-lens alter, resulting in changes in function: there is a gradual depletion of the focussing amplitude from infancy to middle age, and a loss of transmittance in the later decades of life. The optical properties of the lens depend o n its power, which in turn is determined by its physical dimensions (c urvatures and thickness) and its refractive index as well as transmiss ivity and the organization of its internal components. The power of th e functional lens is, however, modifiable by virtue of the lens being attached via the zonule to the ciliary muscle. The contraction and rel axation of the latter respectively increases and decreases lens power in accordance with innervations determined by the physical distance of external objects to be imaged on the retina. This review will conside r many of these features and how alterations in any of them may lead t o changes in lenticular function. However, as we have recently devoted a detailed study to presbyopia [1] its mechanism will not be consider ed here.