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|UsherNet.org > What is Usher-Syndrome > Usher Study by Mary Guest > Retinitis Pigmentosa|
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This term describes not one disease but a group of hereditary diseases of the retina. The retina is the light sensitive tissue inside the eye in which the first stages of 'seeing' take place. With RP the retina slowly degenerates and loses its ability to transmit pictures to the brain. In advanced stages characteristic clumps of pigment appear on the retina and can be seen through an ophthalmoscope.
The first symptom to appear in RP is night blindness; this may also be coupled with difficulty in adapting to bright light or rapidly changing light conditions. Difficulty with dark adaptation can occur in childhood, and although it may be noticed it is seldom attributed to RP, but rather clumsiness, stupidity or even lack of carrots.
Narrowing of Field Vision
In one form of retinal degeneration the rod cells which lie on the periphery of the retina gradually lose function and fail to transmit information about changes in light levels and shapes of objects on the periphery. This loss of visual field or Tunnel Vision, as this is commonly known, means that the individual loses his or her ability to locate objects which are not directly in front, so that for instance, he may still be able to read the bus timetable but unable to locate the bus station without help.
Loss of Central Acuity
Another form of retinal degeneration causes the cone cells to be affected initially so that the individual can no longer see the details of the object in front of him and he will be unable to read print. This type of loss is referred to as macula degeneration and in this case low vision aids such as hand magnifiers and magnification of print using a closed circuit television screen as well as large print texts may be helpful.
In both forms of retinal degeneration the extent and speed at which vision deteriorates is extremely variable. In some individuals the breakdown of the retina is so marked that at the age of six they require special education for the visually impaired and are on the blind register.
Others may have noticed no severe restriction of vision until they reach their thirties and it is not uncommon for some to retain their reading vision well into old age.
In the Usher syndrome form of the disease the retinal condition tends to be diagnosed later rather than earlier in the life of the deaf person and affected individuals may not know they have RP until they have reached young adulthood.
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