What is it?
A cataract is a clouding of the lens of the eye. This leads to decreased vision. A cataract often develops slowly, and it’s symptoms include seeing blurry images with faded colors, and having trouble with both too much and too little light. It is estimated that cataracts are the cause of half the blindness cases and a third of the visual impairment cases worldwide. Cataracts become more common with age, and over half of those over 80 in the US are thought to be affected.
What causes it?
Age is the most common cause of cataracts. Conditions such as diabetes and high blood pressure and environmental factors such as toxins and UV light can also speed up the process that leads to them. Physical injuries to the eye and electrical shocks are also significant causes. Some genetic conditions can lead to cataracts at an early age.
What happens during it?
The mechanisms of cataracts are complex and not fully understood, and there are several different types of the condition which all differ in how the disease comes about. It is thought that one of the most common forms, the age-related cataract, results when normal age-related processes are accelerated.
The lens is the part of our eye that helps refract light so that it can be collected into a small area in the back of our eye. It can change shape to help us focus on objects that are far away or very close – the incorrect function of this shape-altering is often the reason why people need glasses.
It is thought that due to things like exposure to UV light, the structure of some proteins inside the lens starts to change. This causes them to aggregate together. When these aggregates become big enough, they can block the light from entering further into the eye or make it scatter to areas in which it cannot be interpreted.
Another factor leading to cataracts in old age is the decreased function of the cells in the outer layer of the lens. These cells are supposed to produce fibers that in turn help make the lens more transparent. If the amount of these fibers is altered through the loss of cell function, the lens becomes less transparent and hence the affected person will see less.
How can it be treated?
While in those cases where the vision can be corrected with glasses or contacts this is usually recommended, more severe cataracts are treated with surgery. The faulty lens is removed and then replaced with a man-made one. Often this is done through breaking the lens with ultrasound waves and then sucking the resulting liquid away. The success rate of cataract surgery is very high, and the vast majority of patients have a significantly improved eyesight after it.
Sources: https://en.wikipedia.org/wiki/Cataract, http://www.oculist.net/downaton502/prof/ebook/duanes/pages/v1/v1c072b.html, http://www.webmd.com/eye-health/cataracts/what-are-cataracts#1, http://emedicine.medscape.com/article/1210914-overview#a6, https://en.wikipedia.org/wiki/Lens_(anatomy)