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Retinitis Pigmentosa
An inherited progressive degeneration in the retina, the light - sensitive
membrane at the back of the eye. Speaking, generically it can be described as a
progressive cause of visual loss, which is attributed to the loss of viable
photoreceptors.
The retina is a delicate layer of cells which picks up the
pictures and transmits them to the brain.
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In humans there are two types of light sensitive cells in the retina: rod cells
and cone cells. Rod cells
 pick
up movement out of the corner of the eye and also, in a normal eye it is the
rods that operate in poor light or at night. There are about 120 million rods in
each eye and they are more numerous towards the outer edge of the retina. The
cone cells are used in colour vision and in close precision work like reading.
There are not as many cones and they are more concentrated in the centre of the
retina (the Macula).
Retinitis pigmentosa is a rare disorder in which the cells in the light -
sensitive retina in the eye are progressively lost. Dark patches of pigment form
on the retina, and vision deteriorates. The disorder is more common in males and
is inherited, usually in an autosomal recessive manner. It may not cause
symptoms until early in adult life. Both eyes are affected equally.
Causes
 Retinitis
Pigmentosa can be inherited from our parents as genes carry family traits like
eye and hair color, the shape of our face, etc. Retinitis Pigmentosa can be
passed to succeeding generations by one of three genetic inheritance patterns—autosomal
dominant, autosomal recessive, or X-linked inheritance.
RP may be caused by a breakdown in the function of the rods or the cones in some
part of the retina. The retina is so complex that breakdowns may occur in a
variety of ways and so RP is not a single disorder but a great number of
disorders. The breakdown of cone function may be called
Macular Degeneration.
There are other disorders similar to RP like Gyrate Atrophy, Choroideremia etc.
The common feature is the degeneration of the retina for one reason or another.
Researchers are trying to find particular causes of retinal disorders.
Symptoms
If you have retinitis pigmentosa, the first symptom you may notice is poor
vision in dim light. Later, the outer edges of vision, known as peripheral
vision, are lost, and sight deteriorates progressively inwards until only a
small area of central vision remains. Rarely, tunnel vision can cause blindness
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Difficulty in seeing at night or in poor illumination. Most forms of RP first
cause the degeneration of rod cells. These forms of Retinitis pigmentosa,
sometimes called rod-cone dystrophy, usually begin with night blindness.
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Glare.
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Eye fatigue (from straining to see).
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Low light to dark adaptation times and poor contrast sensitivity.
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  Other forms of Retinitis Pigmentosa, sometimes called cone-rod dystrophy, first
affect central vision. Patients first experience a loss of central vision that
cannot be corrected with glasses or contact lenses.
Diagnosis
 Retinitis pigmentosa is diagnosed by
examining the retina with an
ophthalmoscope, an instrument which directs a beam of light into the eye. The
classic sign of RP is clumps of pigment in the peripheral retinal called "bone-spicules."
A test called electroretinography (ERG) may also be ordered to study the eye's
response to light stimuli. The test gives the health care provider information
about the function of the rods and cones in the retina.
Treatment
 There is no effective treatment or cure for retinitis pigmentosa (RP). Treatment
aims to decrease further vision loss and to help you function with the vision
that you have. Your doctor can counsel you about expected patterns of vision
loss based on the type of retinitis pigmentosa you have.
Although the condition is untreatable, special
glasses may help to widen the
field of vision if your visual loss becomes severe. Also, the use of sunglasses
to protect the retina from ultraviolet light may have a vision-preserving
effect.
For people with Retinitis Pigmentosa a daily dose of 15000 International units
of Vitamin A Palmitate (only) has been shown to slow the degeneration of the
cone ERG. A blood test must be taken to ascertain liver function and Vitamin A
levels in the blood BEFORE taking this treatment. Pregnant women must not take
high doses of Vitamin A under any circumstances and this treatment must be
undertaken in consultation with your doctor or eye specialist.
Using Low-vision aids
These include the following:
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 Magnifying glasses
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 Electronic magnifiers, which project an enlarged image onto a screen
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 Night vision scopes, which enlarge distant objects under conditions of low light
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 Lenses for distant vision (eyeglasses or contacts)
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If you plan to have children, you may wish to have genetic counseling to assess
the risk of the abnormal gene being inherited.
Related Links
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