The lens is a clear, flexible, biconvex structure suspended behind the iris by the zonular fibres. It has no blood vessels or nerves and keeps adding new fibres throughout life, so it grows larger and stiffer with age. By changing shape it lets the eye switch focus between far and near objects.
| Location | Behind the iris and pupil, in front of the vitreous body |
|---|---|
| Parts |
|
| Nerve Supply | None (avascular and non-innervated) |
| Blood Supply | None; nourished by the aqueous humour |
Fine-tunes the focusing of light onto the retina and changes its curvature for near vision (accommodation). It also filters some ultraviolet light.
Clouding of the lens (cataract) is the leading cause of reversible blindness worldwide and is treated by removing the lens and implanting an artificial one. Loss of lens flexibility with age causes presbyopia, the need for reading glasses after about 40. Weak zonules in Marfan syndrome let the lens shift out of position (ectopia lentis).
Progressive opacity of the lens causing blurred vision, glare and faded colours. Risk factors include age, diabetes, smoking, steroids and ultraviolet exposure.
Displacement of the lens from weak or broken zonules, seen in Marfan syndrome, homocystinuria and trauma.
Age-related loss of the lens's ability to change shape, making near focus difficult from the mid-40s onward.
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