Most common conditions causing low vision:
Age-related Macular Degeneration
An eye disease that results in a loss of central vision leaving only side or peripheral vision intact. Age-related Macular Degenration (AMD) is the leading cause of vision loss in older people. Macular degeneration affecting younger people is called “macular dystrophy” and can run in families.
There are two types of AMD, dry and wet and both can lead to severe vision loss. AMD affects the macula, the small central part of the retina responsible for central and detailed vision. It is not painful but cells in the macula break down causing this loss of central vision.
Dry AMD – This is the most common form of the disease, affecting about 90% of those with AMD. It has a more gradual onset and generally occurs when the waste products are not carried away from the macula as effectively resulting in a collection of yellow fatty deposits called drusen. This gradual deterioration of the macula usually occurs over many years and vision changes are much more subtle.
Wet AMD – This is much less common and occurs when tiny new abnormal blood vessels begin to grow in or under the retina.. These then leak blood and fluid which damages the macula. Wet AMD results in a more severe and sudden loss of central vision.
Signs of AMD
As the cells in the macular deteriorate the ability to see clearly will change. Objects directly in front may appear to change shape, size or colour. Vision may become blurry, lines become distorted or dark spots may appear in the centre of the image. The central part of the retina, which is responsible for detail, colour and daylight vision is damaged. Reading can become difficult and colour vision reduced and there may be a need for increased light.
Risk factors for AMD
These include age, high cholesterol and high fat diets, untreated high blood pressure and smoking, all of which can result in poor circulation to the retina. A lack of certain nutrients needed by the retina can increase the risk and can be helped by eating a balanced diet rich in fruit and green leafy vegetables. Excessive sunlight and harmful UV light is also a risk factor and can be helped by wearing good sunglasses. Some families have a history and greater tendency for the condition and women are also more likely to develop AMD than men
Test yourself
Using the Amsler grid you can test yourself to check for any distortions or abnormalities in your vision.
How to use the Amsler Grid
- Hold the grid at normal reading distance using your reading glasses if you have them.
- Cover one eye and look at the black dot in the centre.
- Whilst looking at this central spot see if all the lines appear straight and even. Check that none are wavy, distorted or missing.
- Then cover your other eye and repeat.
- If you notice any abnormalities in your vision consult your optician or ophthalmologist straight away.
This test can give an indication but is not a substitute for a full eye examination which you should have to check your vision at least every 2 years.
Diabetic Retinopathy
Diabetes is a chronic disease related to high blood sugar that may lead to vision loss. Most sight loss due to diabetes can be prevented but early diagnosis is vital which is why diabetic patients should have an annual eye examination. Diabetic retinopathy can be one of the complications of advanced or long-term diabetes.
Diabetic retinopathy affects the network of blood vessels lying within the retina which can leak and damage the entire retina including the macula. The vessels may leak blood and fluid in the early stages and can result in blocked vessels in later stages which means new weaker blood vessels will grow in the eye. These new vessels can grow in the wrong place and can leak and cause scarring which can pull and distort the retina and can lead to retinal detachment.
Laser treatment of localised areas of leakage can maintain vision levels but will not regain vision lost. Vision can generally be maintained provided treatment is started early enough and may help to avoid the later stage complications.
Glaucoma
An eye disease, related to high pressure inside the eye that damages the optic nerve and leads to vision loss. Glaucoma affects peripheral, or side, vision. It can also affect central vision in the later stages of the disease. The optic nerve carries information from the retina, the light sensitive layer in the eye, to the brain which it sees as a picture. Progressive damage to the optic nerve from a build-up of pressure inside the eye due to ineffective or blocked drainage channels can be detected through eye examinations and special tests.
In the early stages there may be little effect realised as changes to the field of vision are very subtle. A loss of contrast or difficulty driving at night may be an indication. Early loss is sometimes in the shape of an arc a little above or below the centre when looking straight ahead but if untreated will spread out and up to eventually form what is known as “tunnel vision”, like looking through a long tube.
Treatment can be in the form of eyedrops to reduce the pressure in the eye and if needed laser treatment to open the drainage channels. For acute glaucoma where pressure rises rapidly, pain accompanies the condition and hospital treatment will be needed to relieve both the pain and the pressure using drugs and laser treatment or a small operation to reduce the obstruction to the drainage channels.
Cataracts
A cataract is a clouding of the lens that reduces the clarity of the vision so that people see through a haze and there may be an increase in sensitivity to glare so that halo’s appear around bright lights. There may also be a loss of contrast and trouble distinguishing colours as the lens becomes more yellow with age e.g. it may be difficult to tell the difference between similar colours such as navy blue and black. In advanced stages it can be harder to read as the printed letters can appear faded and not as distinct.
Some factors can increase the risk of cataracts such as excessive exposure to sunlight, smoking and high cholesterol. In a usually safe and successful short operation, the cloudy lens can be replaced with a plastic lens to remove the symptoms. Cataract surgery has a high success rate in normal eyes. There may be a need for distance and reading glasses once the plastic lens is in place as it will not have the accommodation of the eye’s normal lens.
Retinitis Pigmentosa
Retinitis Pigmentosa is an inherited disease affecting the retina. It is caused by a breakdown in the function of the rods, which control night vision, the cones, or in some cases a failure in another part of the retina. The retina is so complex that damage can occur in a number of ways. Retinitis Pigmentosa is not a single disorder but a group of related disorders leading to visual loss.
Different types of Retinitis Pigmentosa can have different symptoms. The most common type of early symptom is difficulty seeing at night or in dark rooms. It can also lead to tunnel vision where side vision is lost. In another type of Retinitis Pigmentosa the side vision is retained but there is a loss of central vision leading to difficulty with reading and close tasks.
Each person has a different rate of sight loss. For some, the loss of sight is slow and there may be only a small loss over perhaps ten years or more. Others have periods of rapid loss, often with years in between with no apparent decline. Some will have been aware of poor vision since their childhood or teens. If the retinitis pigmentosa runs in the family, the pattern could be the same within that family. Usually the loss is gradual enabling people time to adjust.
Retinitis pigmentosa can eventually lead to blindness but usually most people retain a small amount of vision although they are termed "blind" for legal purposes.
If you notice a change in your vision or are concerned about it, then it is important to visit your optician or GP as soon as possible.
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