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Wales Council for the BlindEye Conditions Information Pack[back to
general contents] Contents
IntroductionLess than ten percent of visually impaired people are totally blind, with no vision at all. This means that the majority of visually impaired people do have some useful vision. There are several reasons for loss of sight; congenital diseases from birth, hereditary conditions, accidents, diseases and age can all have an effect on someone's sight. Effects and levels of vision cannot be generalised, as each individual is different, and people can experience differing effects even from the same condition, depending on how far the disease has progressed, their mood, the weather, their weariness etc. The images contained within this pack are some of the most common eye diseases, and are by no means exhaustive. They are not simulations of the eye conditions, but merely represent a glimpse of the varying ways that people see so that you can have some understanding. In reality, the person does not see ‘black patches’ or ‘blobs’. What they see are simply areas of non-vision, known as scetomas. A scetoma is not just one area; it can be several lumps together and therefore there is no uniform shape i.e. the area of non-vision is unlikely to be a perfect circle. If you would like further information regarding any of the eye conditions in this pack, or any other conditions, we would be very happy to help by supplying materials or putting you in touch with experts in the field. You can contact us at the Training Unit at the address at the end of this information pack. Macular Degeneration
One of the most common causes of visual impairments in Western society, Macular Degeneration can come in two forms; Dry and Wet Macular Degeneration. Age Related or Dry Macular Degeneration results from when the blood supply is no longer able to nourish the centre of the retina, the macular, effectively. As we get older and our blood supply becomes less efficient, the macular becomes less sensitive, and the cones – which supply us with the detail and colour of our vision – clustered within, die off. The macular does not wear out or disappear – it simply stops functioning as efficiently as it once did. Symptoms include a ball of mist in the centre of the field of vision, like scratches on glasses, and less definition of colour and detail. It is important to stress that you cannot become completely blind through macular degeneration, although there is, at present, no treatment or cure. Wet Macular Degeneration (not pictured), is caused by swelling. As the layers swell further and further, they push the retina forward, causing haemorrhaging and blood to leak into the vitreous humour. Although this will eventually heal, the scarring that remains results in a loss of vision in the scarred area. Symptoms of Wet Macular Degeneration include a distortion of vision – objects ‘have a kink’. Diabetic Retinopathy
This is the most common cause of total blindness, although only 4% of people with diabetes are affected with diabetic retinopathy, and only when the disease is not properly controlled. The diabetes, which affects the blood supply, causes haemorrhaging in the eye, and the blood leaks into the vitreous humour. Although new blood cells grow on the retina, weakened, they break leaving a lot of blood and gunge. As the weight becomes heavier on the retina it can cause the eventual retinal detachment. Diabetic Retinopathy can be prevented by controlling the diabetes, and by having regular checks at the diabetes clinic, ( 3-6 month intervals ). When the diabetes cannot be stabilised, preventative laser work can be used. Retinitis Pigmentosa
An umbrella term, Retinitis Pigmentosa covers 29 different types of tunnel vision, although with R.P., it is not just the peripheral vision that can become restricted – the central vision can also be affected. As the pigmentry layer within the retina thickens, the retina loses its ability to absorb light effectively, resulting in the retina sending incorrect, or false messages that confuse the brain. The cones and nerve endings in the retina die off, leading to a lack of visual information, which, in turn, leads to a loss of field of vision (reverse retinitis pigmentosa, starts with the vision deteriorating in the centre, and works its way out to the periphery). Usually identified in the teenage years, the classic progression of the disease is gradual. Symptoms vary from individual to individual, and people who have R.P. over 40 years old seem susceptible to developing cataract. R.P is often referred to as ‘night blindness’; when there is too little. The reverse is possible on a bright sunny day when there is too much light. Glaucoma
Another form of tunnel vision, glaucoma can affect the eye in three differing ways, although all are caused by an imbalance of aqueous humour at the front of the eye and the effective drainage of this fluid away from the eye. Unlike retinitis pigmentosa, people with glaucoma often have good central vision. Chronic (simple) Glaucoma results from when too much fluid is produced, and the eye is unable to drain it away properly. Pressure builds up, causing the cornea to bulge and push the sides of the eye (sclera), crushing the optic nerves. As this form of glaucoma is relatively painless, a person can lose up to 60% of vision and not know. If detected early enough, drops can be prescribed to inhibit production of the fluid, and patients are able to live as full a life as before. However, it must be stressed that these drops are only a preventative method- not a cure. Once vision is lost, it cannot come back and the drops must be continued to prevent the symptoms recurring. Acute Glaucoma is caused when drainage from the eye is completely blocked, and can be very painful. Needing immediate treatment, laser surgery is used to burn a hole into the blockage, which then allows drainage. When not enough aqueous fluid is produced, this is called Negative Glaucoma; the pressure in the vitreous humour pushes the front of the eye. As with all forms of glaucoma, drops can help balance the fluid effectively, although they still cannot restore vision or cure the disease. Everyone over forty years of age should receive regular checks for glaucoma, particularly if glaucoma runs in the family. If there is a history of glaucoma in the family, glaucoma checks can be offered without cost. Hemianopia
Caused mostly as a result of a stroke or head injury, a legion blocks the optic pathways to the brain, and is the only image pictured within this pack that illustrates a visual impairment that is not the result of a disease, or because the eyes are not functioning properly. Usually half of the sphere of sight is missing, although individuals can also be affected so that a quarter or three quarter of their vision is lost, and the division may not necessary be vertical – a horizontal split can occur. Some people with hemianopia are oblivious to the hemiopic side i.e. the brain ignores the side with no vision, although, providing the brain can heal itself and the blockage to the optic pathways is removed, sight can be restored. Cataract
The example produced here is a cataract senile – a well advanced illustration of a cataract. The lens of the eye, constructed similarly to how an onion is made up, has transparent, individual leaves. One leaf at a time becomes opaque, which causes the light to scatter and stops the light filtering through properly. Not a growth over the eye, cataracts affect people of all ages, despite the popular misconception that only the elderly are affected; some can be born with them. Symptoms of cataract include loss of definition of colour and detail. It can today be treated successfully where the lens is entirely removed, and an implant lens put in its place. Additionally, there is a possibility that the capsule, which holds the lens, could also become opaque. This can be treated successfully with a laser. For further information, or for details on how to obtain an extra copy of this pack, please do not hesitate to contact us at: Wales Council for the Blind, Telephone: (UK) 01222 473954 Material written and prepared by Vicky
Richards, Training Development Officer; Copyright Wales Council for the Blind, 1997. |
