Eye lens

The eye lens is a clear, biconvex (convex on both sides) structure in your eye, roughly the size of a pea. It lies directly behind the iris and the pupil, and is held in place by thin fibres that connect it to the ciliary body. The lens consists largely of water and proteins, and has no blood vessels or nerves, which is why it remains transparent.

The main function of the eye’s lens is to focus light entering through the pupil so that it is sharply focused on the retina at the back of the eye. The muscles of the ciliary body enable the lens of the eye to change shape: it becomes more curved to see clearly at close range (accommodation) and flatter to see clearly at a distance. This ability to accommodate diminishes with age, which you will notice as you get older and find it difficult to read at close range.

The eye lens continues to grow throughout your life, albeit very slowly. As you get older, the lens becomes thicker and less elastic. This can lead to presbyopia (age-related long-sightedness) and, eventually, to clouding of the lens, known as a cataract.

Accommodation and sharp vision

The eye’s lens constantly adjusts to enable us to see objects at different distances clearly. This process is called accommodation. When looking at something close up, the ciliary muscles contract, causing the lens to become more rounded and increase its refractive power. When looking into the distance, the muscles relax and the lens becomes flatter. This happens automatically and subconsciously.

Changes with age

From the moment you are born, the eye’s lens continues to grow slowly. Around the age of forty, the lens begins to lose its elasticity, making it harder to focus. This is a normal part of ageing and leads to presbyopia: you will often need reading glasses or multifocal lenses to see clearly at close range. Later in life, the lens can become cloudy, a condition known as a cataract. This is a gradual process in which vision becomes blurred or less clear.

The eye lens and refraction

Together with the cornea, the eye lens is responsible for the refractive power of your eye. The cornea accounts for the majority of the refraction, but the eye lens fine-tunes this by accommodating. If the eye’s lens refracts light too strongly or too weakly in relation to the length of your eye, refractive errors such as short-sightedness, long-sightedness or astigmatism occur. These are usually corrected with glasses or contact lenses.

When should you see an optician?

Changes to the eye lens are often a natural part of ageing, but sudden changes in your vision, blurred vision, halos around lights or reduced colour vision may indicate a lens disorder. If you have any of these symptoms or are unsure, please have them assessed by your optician, optometrist or ophthalmologist.