According to the recent survey on blindness and low vision carried out in Nigeria between 2005 and 2007, the leading causes of blindness are Cataracts, Glaucoma, Onchocerciasis, and corneal blindness. Refractive errors and low vision contribute significantly to correctible visual impairment. It is therefore imperative that we give you some information on these disorders. We start with Cataract.
A cataract is a clouding of the eyes natural lens, which is behind the iris and pupil. The lens works much like a camera lens, focusing light unto the retina at the back of the eye. The lens also adjusts the eye focus, letting us see things clearly both up close and far away. It is usually clear and transparent allowing light to pass through to the retina where image is formed and the information is converted to electrical impulse and transmitted to the brain through the optic nerve. The lens is mostly made of water and protein. The protein is arranged in a precise way that keeps the lens clear and allows light pass through it. As we age, some of the protein may clump together and start to cloud a small area of the lens. This is the way cataract is formed, and overtime, it may grow larger and cloud more of the lens, making it harder to see.
Researchers are gaining additional insights about what causes the specific types of protein (crystallins) to cluster in abnormal ways to cause lens cloudiness and cataracts. One recent finding suggests that fragmented versions of these proteins bind with normal proteins, thus disrupting normal function.
Cataracts are classified as one of three types:
A nuclear cataract is most commonly seen as it forms. This cataract forms in the nucleus, the center of the lens, and due to natural aging changes.
A cortical cataract which forms in the lens cortex, gradually extends its spokes from the periphery of the lens to the center. Many diabetes develop cortical cataracts.
A subcapsular cataract begins at the back of the lens. People with diabetes, high far sightedness, retinitis pigmentosa or those taking high doses of steroids may develop a subcapsular cataract.
Cataract Symptoms and signs
A cataract starts out small and at first has little effect on your vision. You may notice that your vision is blurred a little, like looking through a cloudy piece of glass or viewing an impressionist painting. A cataract may make light from the sun or a lamp, seem too bright or cause glaring therefore the vision is worse in the sun and bright light due to glare.
You may notice when you drive at night that the oncoming head lights produce more glare than before. Colours may not appear as bright as they once did. Cataract affects vision by scattering incoming light. People with cataract usually complain of blurring and foggy vision, seeing some parts of an object clearly while other parts are blurred.
The type of cataract you have will determine exactly which symptoms you experience and how soon they will occur. When a nuclear cataract first develops it can bring about a temporary improvement in near vision, called “second sight”. Unfortunately, the improved vision is short lived and will disappear as the cataract worsens. Meanwhile, a subcapsular cataract may not produce any symptoms until it’s well-developed.
Cataract occurs as a result of derangement in the metabolism of the fibers that make up the lens of the eye which normally grows throughout life. The fibers are made up of protein and in the normal state are arranged in such a way as to be transparent, allowing light to pass through. Impairment of the metabolism as a result of injury, ultraviolet light from the sun, excess sugar, genetic predisposition among others ultimately leads to the lens fibers becoming opaque, scattering light, and not allowing the focus of light from an object on the retina.
The most important cause of cataract is the aging process in the eyes. Other important causes include: injury, diabetes mellitus, infections, inflammations, tumours, Cigarette smoke, air pollution, heavy alcohol consumption, high farsightedness, retinitis pigmentosa. Those taking high doses of steroids may develop a subcapsular cataract.
Aetiopathogenesis : What causes cataracts?
No one knows for sure why the eyes lens changes as we age, forming cataracts, researchers are gradually identifying factors that may cause cataracts and information that may help prevent them.
Many studies suggest that exposure to ultra violet light is associated with cataract development, so eye care practitioners recommend wearing sunglasses and a wide brimmed hat to lessen exposure.
Other types of radiation may also be causes. For example, a 2005 study conducted in Iceland suggests that airline pilots have a higher risk of developing nuclear cataract than non pilots and that the cause may be exposure to cosmic radiation. A similar theory suggests that astronauts too are at risk from cosmic radiation.
Other studies suggest people with diabetes are at risk for developing cataract. The same goes for users of steroids, diuretics and major tranquilizers, but more studies are needed to distinguish the effect of the disease from the consequences of the drugs themselves.
Prevention: A diet high in anti oxidant such as beta carotene (vitamin A), Selenium and vitamin C and E may delay cataract development, meanwhile eating a lot of salt may increase risk. Some eye drops are also used to slow down the development of cataracts.
Treatment. Think about surgery when your cataracts have progressed enough to seriously impair your vision and affect your daily life. Many people consider poor vision an inevitable fact of aging, but cataract surgery is simple, relatively painless procedure to regain vision.
During surgery, the surgeon will remove your clouded lens and in most cases replace it with a clear, plastic intraocular lens (IOL)
Glasses may be used at the early stage to improve vision.