The crystalline lens, or lens, is a bi-convex structure in the eye that is transparent and which works with the cornea to refract light to focus on the retina; it’s very similar in its working to a manmade spectacle lens.
It’s this lens which changes shape to help the eye alter its focal distance so it can focus on objects at varying distances.
In effect, it means that the person can create a sharp real image of the object being viewed to be formed on the retina of the eye.
The working of the lens as it adjusts, it is properly known as ‘accommodation’, is very similar to the process that a camera would use by moving its lenses to focus on an image.
Interestingly, the crystalline lens is more flat on its front side than on the rear.
How does the crystalline lens work?
The amount of light entering the eye is controlled by the iris, which sits in front of the lens.
The lens itself is ellipsoid in shape and it never stops growing as a person gets older; in adults, the lens is around 10 mm in diameter.
The lens actually consists of three parts: there is the lens capsule, which forms the outermost layer; the lens epithelium, which sits between the lens capsule and the outermost layer and the lens fibres, which make up most of the lens.
For the lens to work, the ciliary muscles change the shape of the lens which enables the eye to focus on objects at different distances.
There are a number of potential problems with the crystalline lens with perhaps cataracts being the best known. Cataracts themselves are opacities of the lens and some may be small and not need treatment while others will be big enough to block light and perfect vision.
What are cataracts?
Cataracts usually develop as the lens becomes older and more opaque but they can be formed after an injury to the lens itself or congenitally. Diabetes is also a major factor in the development of cataracts.
Cataracts can be operated on and the surgery will see the removal of the lens and an artificial intraocular lens being inserted in its place. Find out more about intraocular lens surgery here (link to procedure page?)
Other issues affecting the crystalline lens are presbyopia, which is the inability to focus on nearby objects and is generally age-related; ectopia lentis, which is when the lens is displaced from its position and aphakia which is when there is no lens present in the eye, usually the result of injury or surgery but it could also be congenital.