The lens consists of a central nucleus surrounded by lens fibres and encapsulated in an elastic envelope. It is a transparent, biconvex structure – with the anterior surface being flatter than the more curved posterior surface. The anterior surface fills the pupil and the posterior surface contacts the vitreous.
The lens sits in the patella fossa and is held in place by the lens zonules or suspensory ligaments. Changes in the tension of the zonules alter the shape of the lens, and change its optical power.
The adult lens does not have a blood supply, and therefore relies on the aqueous for the provision of oxygen and nutrients and the removal of waste. Disturbances in the aqueous can therefore affect lens metabolism and transparency.
As an animal ages, new lens cells are produced at the periphery and older cells move towards the lens nucleus. This means that with time, older cells become denser and more tightly packed – this causes a visible grey haze in the lens and is known as nuclear sclerosis. This differs from a cataract, which is a term used to describe a group of ocular conditions which present as opacity of the lens or its capsule.
