Retinitis Pigmentosa is the name of a group of retinal dystrophies that cause degeneration of the retina of the eye. Retinitis pigmentosa is a disease of the eye that the affected individual is born with. The word "retinitis" derives from "retina" (a part of the eye) and "itis" (a disease). It is a disease of the retina, though not a contagious one. The word "pigmentosa" refers to an associated discoloration of the retina, which becomes visible to an eye physician on examination. For those people who find retinitis pigmentosa a difficult term to use, the shortened form "RP" serves as a simpler alternative.
The retina is located at the back of the eye and is connected to the brain. It is made up of many millions of light-sensitive cells known as photoreceptor cells. These photoreceptor cells have the vital function of transmitting electrical impulses to the brain to enable seeing to take place.
Retinal dystrophies are caused by the gradual breakdown of these photoreceptors. Therefore it is important to understand the structure of the eye (as well as the ear in Usher Syndrome).
The eye consists of several parts that resemble a camera (see diagram).
When you see an object, the light travels from that object to the cornea, then passes through the aqueous humour, pupil, lens and vitreous humour to reach the retina. During this passage, the light becomes focused onto the macula.
At the macula, the light causes chemical reactions in the cones, that consequently send electrical messages from the eye to the brain. The brain recognises these messages and indicates to you that this particular object has been seen. The cones are therefore responsible for you being able to recognise colours and to read.
The rods are essential for you to see in the dark, and to detect objects to the sides, above and below the object on which you are directly focused. This function prevents you from bumping into obstacles when moving around.
All the retinal cells (rods and cones) are provided with oxygen and other nutrients from the retinal pigment cells (epithelium), which are kept supplied by the rich network of blood vessels in the choroid.
It is thought that one child is born with RP in approximately every 3,000 births in Australia. It is important to recognise that it is no one's fault and that RP can strike in a family with no known history of it. In fact, RP results from an imperfection in a tiny gene that causes an incorrect protein to be supplied to the retina. Over time this causes photoreceptor cells to die and progressive loss of
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David Shanahan © 2009