GLOSSARY

The lens is a transparent, biconvex, flexible structure behind the iris and pupil that changes shape to focus light precisely on the retina; this process is called accommodation.

Structure

• Capsule: an elastic outer covering.
• Lens fibres: cells with no nucleus and no blood supply, filled with crystallin protein, which gives transparency.
• Suspensory ligaments (zonules): attach the lens to the ciliary body.
• Lifelong growth: new layers are added throughout life, so the lens gradually becomes thicker and stiffer.

Mechanism of Accommodation

• Distance vision: the ciliary muscle relaxes → the ligaments pull → the lens flattens (less power).
• Near vision: the ciliary muscle contracts (parasympathetic) → the ligaments slacken → the lens becomes rounder (more power).

Clinical Application