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Retinitis Pigmentosa
Retinitis pigmentosa (RP) is the name given to a group of inherited diseases that affect
the retina. They are characterized by a gradual breakdown and degeneration
of photoreceptor cells, which results in a progressive loss of vision. It is estimated
that RP affects 100,000 individuals in the United States.
Clinical Description
RP causes degeneration of the retina, a delicate tissue composed of several cell layers
that line the inside of the back of the eye and contain photoreceptor
cells (rods and cones). The rods are concentrated outside the center of the retina, known
as the macula, and are required for peripheral vision and for
night vision. The cones are concentrated in the macula and are responsible for central and
color vision. Together, rods and cones are the cells responsible
for converting light into electrical impulses that transfer messages to the brain where
seeing actually occurs.
The most common feature of all forms of RP is a gradual breakdown and degeneration of the
rods and cones. Depending on which type of cell is predominantly
affected, the symptoms vary, and include night blindness, lost peripheral vision (also
referred to as tunnel vision), and loss of the ability to discriminate
color before peripheral vision is diminished.
Symptoms of RP are most often recognized in adolescents and young adults, with progression
of the disease usually continuing throughout the individual's
life. The rate of progression and degree of visual loss are variable.
Inheritance
RP can be passed to succeeding family generations by one of three genetic inheritance
patterns: autosomal dominant, autosomal recessive, or X-linked inheritance.
Because RP is an inherited disorder, it can potentially affect other family members. There
are also cases of isolated inherited RP as well. Individuals
of an affected family may not experience the same intensity of symptoms and as a result
may not recognize that they have RP and need medical consultation.
If one member of a family is diagnosed with a hereditary retinal degeneration, it is
strongly advised that all members of that family contact an ophthalmologist.
Treatment
As yet, there is no known cure for RP. However, intensive research is currently under way
to discover the cause, prevention, and treatment of RP. At this
time, RP researchers have identified a first step in managing RP. While not a cure,
certain doses of vitamin A have been found to slightly slow the progression
of RP in some individuals. An information packet on this research breakthrough is
available from The Foundation. Researchers have found some of the genes
that cause RP. It is now possible, in some families with X-linked RP or autosomal dominant
RP, to perform a test on genetic material from blood and other
cells to determine if members of an affected family have one of several RP genes.
Related Diseases
There are other inherited retinal degenerative diseases that share some of the clinical
symptoms of RP. Some of these conditions are complicated by other
symptoms besides loss of vision. The most common of these is
Usher syndrome,
which causes both hearing and vision loss. Other rare syndromes that researchers are
studying with funding from The Foundation Fighting Blindness include
Bardet-Biedl (Laurence-Moon) syndrome, Best disease, choroideremia, gyrate-atrophy,
Leber Congenital Amaurosis,
and
Stargardt Disease.