Eye cataracts are common causes of loss of vision in the elderly. Learn how a cataract affects the eye lens.
An eye cataract is a very common eye condition that nearly everyone develops after a certain age. While for most people a cataract means an eye operation, it is still a leading cause of blindness in many developing countries. Why does this eye problem occur with advancing age? How exactly does it affect the eye? Read on to find out the story behind eye cataracts.
What is a Cataract
The word is derived from the Latin word ‘cataracta’ which means waterfall, probably for the clouding of vision it causes. Cataracts only affect one part of the eye – the crystalline lens. Each eye is equipped with a biconvex, transparent lens that plays a very important part in focusing light rays entering the eye onto the retina. The lens has the capacity to alter shape so that the eye can have both near and distant vision.
The important thing here is that the eye lens is transparent. It has to be, in order to allow light rays to enter the eye. Cataracts cause the eye lens to become opaque, blocking light entry and leading to loss of vision.
How the Eye Lens Becomes Opaque
There are many factors that help the crystalline lens maintain transparency. These are:
• The lens has no blood vessels running through it
• Its cells are tightly packed together
• It has special arrangement of its proteins and fibres
• It maintains a relative state of dehydration (requiring a fine water-salt balance)
Conditions that disturb any of the above factors, especially the critical water-salt balance or the lens protein arrangement, could lead to a loss of transparency.
Advancing age brings with it many biochemical changes in the body. In the lens, there is a decrease in the protein levels. There is also a decrease in potassium levels with a corresponding increase in sodium levels, this scenario being the reverse of the normal state. This leads to disturbance of the water-salt balance and cause hydration or water-logging of the lens, view website.
Other age-related changes like nuclear sclerosis, compaction of the nucleus, increase in water-insoluble protein content and pigment deposition may also contribute to the loss of transparency as does age-related oxidative damage.
Eye Changes in Cataract
In the initial stages, water-logging causes lens fibers to be separated by fluid. Gradually, small areas of detectable opacities develop with clear areas between them. These opacities occur in different regions of the lens in different types of cataracts.
The cataract gradually ‘matures’ with the opaque area increasing in size. The water-logging may cause the lens to sometimes become swollen, a condition called ‘intumescent cataract’. In the final stage the lens becomes completely opaque, the stage of the ‘mature senile cataract’. This stage may sometimes be followed by ‘hypermaturity’ where the lens fibres just liquefy inside the capsule of the lens or the lens becomes shrunken and wrinkled with leakage of water.
As the lens goes through these stages of opacification, the person develops visual disturbances that can go on to blindness. This condition is treated by eye surgery where the opaque lens is removed and replaced with an IOL or intraocular lens.