Causes
The primary causes of vision loss are eye disease and health conditions, although vision loss can also occur as a result of age, birth defects or injury. In some eye diseases, the symptoms can be incorrectly interpreted as decreasing vision due to ageing.
The most common causes of low vision in western countries are diseases of the macula. The macula is the name given to the area at the very centre of the retina. This region is responsible for detailed central vision and most colour vision. It is responsible for the ability to read, recognise faces, drive a car and see colours clearly. It is also responsible for any other activity that requires fine vision. The rest of the retina is called the peripheral retina. It is used to see general shapes and provides ‘get-about’ vision, which is also called side vision or peripheral vision. Read more about how the eye works.
The most common diseases of the macula are:
Macular degeneration
Macular degeneration is Australia’s leading cause of blindness. It affects one in seven Australians over the age of 50 and the incidence increases with age. The disease causes progressive damage to the macula resulting in central vision loss. Macular degeneration is frequently referred to as age-related macular degeneration.
There are two types of macular degeneration. The dry form results in gradual loss of central vision. The wet form is characterised by a sudden loss of vision and is caused by abnormal blood vessels growing into the retina. It is possible to have macular degeneration in its early stages without knowing. Immediate medical treatment is essential if symptoms occur in order to save sight. Read more about macular degeneration.
Diabetic retinopathy
The most prevalent cause of visual impairment in people who have diabetes is diabetic retinopathy, a condition in which changes occur in the tiny blood vessels that nourish the retina. In the early stages of diabetic retinopathy small blood vessels weaken and leak fluid or tiny amounts of blood which distort the retina. In the more advanced stage blood vessels in the retina are blocked or closed completely and areas of the retina die. Read more about diabetic retinopathy.
Retinitis pigmentosa
Retinitis pigmentosa is a degenerative, hereditary disorder that is often first characterised by night blindness, followed by loss of peripheral vision. It can eventually lead to total blindness. Retinitis pigmentosa is one of many retinal dystrophies and is the leading cause of youth blindness in Australia. It is second only to diabetes as a cause of blindness for those in their twenties and thirties. Retinitis pigmentosa in most cases is hereditary. Read more about retinitis pigmentosa.
Glaucoma
Glaucoma is the name given to a group of eye diseases in which the optic nerve at the back of the eye is slowly destroyed. More often than not this damage is due to a blockage of the circulation of the water (aqueous fluid) in the eye or its drainage.
In other cases, it can be caused by poor blood supply to the nerve fibres, a weakness in the optic nerve or a problem in the health of the nerve fibres.
Glaucoma destroys a person’s vision gradually, starting with the peripheral (side) vision. People can have glaucoma and be completely unaware, as there is usually no pain or early warning signs associated with the most common form of glaucoma. Early detection is critical as any sight lost is irreversible.
Cataract
A cataract is a clouding of the normally clear and transparent lens of the eye.
When a cataract develops the lens becomes as cloudy as a frosted window and light cannot be properly focused on the retina, resulting in an unclear image.
Other retinal dystrophies
While macular degeneration and diabetic retinopathy are the main retinal dystrophies there are many others that can affect eye health. Read more about other macular diseases here.