The Lens

(Fig. 7)  The Lens      

The lens of the eye is a transparent biconvex structure situated between iris and the vitreous

Only that portion of the lens not covered by iris tissue (that is, only that portion directly behind the pupillary space) is visible. The centre of the anterior surface of the lens, known as its anterior pole, is only about 3mm from the back surface of the cornea. The diameter of the lens is about 9 to 10mm. Its peripheral margin, called the equator, lies about 0.5mm from the ciliary processes. It is attached to the ciliary processes and to the posterior portion of the ciliary body by means of the fine suspensory ligaments referred to as the zonular fibres.

The lens is surrounded by a capsule, which is a transparent, highly elastic envelope. The lens material within this elastic bag is rather soft in infants. With age it tends to grow harder, especially toward the centre of the lens. The harder central portion of the lens found in adults 30 years of age or over is referred to as the nucleus of the lens, and the outer lens fibres form the lens cortex. The harder nucleus is a product of the normal development growth of the lens. As new lens fibres are produced, the older fibres are pushed more toward the centre and are compressed in a concentric fashion.

The Vitreous

The vitreous is a jellylike structure, thick and viscous, that occupies the vitreous chamber in the posterior concavity of the globe. Actually, it fills the largest cavity of the eye, occupying two thirds of its volume. It is surrounded in the main by retina. Anteriorly it forms a slight depression behind the lens and is attached to it around the circumference of this depression. Normally the vitreous is quite transparent.

Age-related changes cause the vitreous to become more fluid and particles within it move around and become visible to us. These are known as floaters.