Click here for a printer
friendly version of this page.
The History of Retinitis Pigmentosa
By Cheryll Scarangella
Introduction
Legal blindness is defined by the Social Security Act of 1935 as; visual acuity
for distance of 20/200 or less in the better eye after correction; or visual
acuity of more than 20/200 if the widest diameter of visual field subtends an
angle no greater than 20 degrees (1).
The definition of Subnormal Vision is a statement of the relationship between
visual acuity and visual function, clinically defined as the point at which
the patient becomes aware that his poor vision has affected his performance
in daily life, so that he thinks of himself as handicapped. It cannot be defined
numerically, nor does it include the word "blindness"(2).
The retina is the key structure of the eye. If the retina fails, the eye is
blind, but if there is even a faint glimmer of light, then the possibility of
sight still exists.
The retina is really an extension of the brain, through which the brain receives
information. Pictures are formed on the retina, and are then transmitted by
the optic nerve to the brain.
The retina is made of nerve tissue. It is about as thick as a piece of blotting
paper, and tears as easily as paper does when it is wet. it is transparent,
except for the columns of blood in its own system of blood-vessels. It also
has a second blood-supply from the very rich circulation of the choroid which
surrounds it(3).
Under a microscope the retina is seen to consist of ten layers of tissue, lying
like the pages in a book, The outermost layer, nearest the choroid, is highly
specialized tissue called the pigment cell layer. The other nine layers are
neural tissue. The layer adjacent to the pigment cell layer is the layer of
rods and cones. The remaining eight layers, called the transmitting layers,
send the impulses to the brain by the optic nerve(4).
In a healthy eye, all parts of the retina must work as a team. When one or more
parts of the retina are injured or diseased, visual loss will follow. There
are many diseases that affect the retina including Diabetic Retinopathy, Macular
Degeneration, and Retinal Detachment. Retinitis Pigmentosa, referred to as R.P.,
is another retinal disease upon which I have focused.
What is R.P.?
Retinitis Pigmentosa is a group of inherited diseases that cause degeneration
of the eye's retina. This disease affects 100,000 Americans, and world-wide
the number reaches 1.5 million(5). More than 20,000 people with R.P. are classified
as legally blind.(5).
The retina, which forms the inner wall on the back of the eyeball, is the area
where light coming into the eye registers on the photo- receptor cells, called
rods and cones, and is then transmitted to the brain. When a person has R.P.,
the retina undergoes progressive degeneration because the rods and cones stop
functioning. The visual field is lost because the rods that are scattered throughout
the retina are responsible for detecting movement and shape. They are also accountable
for peripheral vision. The cones discern color and detail, and require more
light to work effectively. The cones are located in the central part of the
retina, called the macula, and are responsible for central vision(6).
R.P. first affects the rods. As the rods are destroyed, vision in low light
decreases and peripheral vision constricts. Further progression of the disease
then affects the cones, leading to central vision loss.
There are several types of R.P.;
I.Congenital R.P. or Leber's Congenital Amourosis is a rare disease apparent
at birth or infancy that causes a steady loss of sight.
2.Autosomal Recessive R.P. which is passed on to a child of two carriers who
may not have RP.. Chances are that:
a). A person with R.P. and an unaffected partner will have a child with R.P.
is I in 160.
b).One known carrier will have a child with R.P. is 1 in 320.
c).Two known carriers will have a child with R.P. is I in 4.
d).One person with R.P. and one carrier will have a child with R.P. is 1 in
2.
e).Two carriers will generate new carriers is I in 2.
f).Two parents with R.P. will have a child with R.P. is 100%.
g).All children of an R.P. parent will be carriers.
h).One out of every 80 people carries the recessive gene for R.P.(7).
3.Autosomal Dominant R.P. is passed to the child of one affected parent and
one unaffected parent. With each pregnancy there is a 50% chance that each child,
male or female, will inherit the disease. Unaffected children usually will not
pass the disease to their children.
4.Sex-linked R.P. is passed to a child by the mother, who is the carrier. Sons
of a female carrier of sex- linked R.P. and an unaffected male have a 50% chance
of having R.P.. Daughters of such a pairing have a 50% chance of being carriers,
but will not inherit the disease.
5.Sporadic R.P., for which the genetic cause and inheritance patterns are still
unknown. Research is ongoing to further investigate new mutations as they are
diagnosed(8).
R.P. occurs as a feature of several other syndromes which include Usher Syndrome,
Bardet-Biedl Syndrome, Mucopolysaccharidosis and Refsum's Disease. When R.P.
is inherited without other disorders the most common form is Autosomal Recessive,
which accounts for an estimated 50-84% of cases. The Autosomal Dominant form
accounts for 10-15%, and Sex-linked R.P. accounts for 5-6%. Female carriers
of the sex-linked form can often be identified through genetic screening(9).
Diagnosing R.P.
R.P. was first diagnosed by Dr. F.C. Bonders, and it was documented in a Medical
Journal called "R.P." by John Hecken- Lively in 1855(10).
Retinitis Pigmentosa is not easily diagnosed. The earliest symptoms are a decrease
in night vision, called Night Blindness, followed by a gradual constriction
of the peripheral field of vision. During an opthalmologic exam there may be
a change in the appearance of the retina, but the only way to accurately diagnose
R.P. is by doing an electroretinogram.
An electroretinogram, or ERG, measures the electrical activity of the retina,
indicating the functional capacity of the rods and cones, when exposed to a
light stimulus. Drops are first placed in the eyes to dilate the pupils. Anesthetic
drops are then administered to numb the eye and contact lenses attached to electrodes
are placed on the cornea. Four more electrodes are the attached, two above the
forehead, and two alongside the eyes. The electrodes record the responses of
the retina, as lights are flashed in both dark and light environmental conditions(11).
The ERG is uncomfortable, and often painful, because a person with R.P. is extremely
sensitive to bright light. The eyes also can become irritated due to the lenses
that were put in, and remain that way for about twenty-four hours.
The results are then recorded on a graph print-out and compared to normal responses
to determine if the patient does have R.P.
There are also tests that determine peripheral vision loss. "Perimetry" tests
the 180 degree field of view for scotomas, which are blind or dark spots in
the visual field. The "Tangent Screen" is a computerized test that tests the
central 25-35 degrees of the visual field. All different color lights are flashed
across a screen, and the patient must push a button whenever they see one of
the lights. The lights range in size, with the largest being about half an inch
in diameter. The results are printed out in a pie-graph, which separates the
best and worst areas of the visual field,by shading the parts of the area of
vision that are affected.
The third test is the "Amsler Grid", which tests the central 10 degrees of vision,
and is mainly used to test for blind spots in the macular area. The macula is
a small area of the retina that surrounds the fovea, and is responsible for
central vision(12),,
Field restrictions are classified as mild, moderate, or severe. Individuals
with mild field restrictions exhibit a loss of peripheral vision so that only
20-40 degrees of central field vision remain. Moderate field restriction is
when the central field of vision is reduced to between 10 and 20 degrees. Severe
field restriction is when the central field of vision is 10 degrees or less(13).
Acuity level, physical disabilities, age, intellectual or emotional problems
and motor difficulties, are a few factors that will also influence the functional
ability of the R.P. patient.
The loss of peripheral fields inhibits the information processing abilities
of the visual system because enough information cannot be taken in at one time.
To compensate, the person must learn to "scan" the environment to obtain all
the important information. The person sees only a small portion at one time,
and the effect is like trying to figure out a puzzle from only one piece of
it. Techniques for adapting to this loss must be taught to people with peripheral
vision loss(14).
Emotional Aspects
People with R.P. who have had sight and then lose it, have a much greater difficulty
in developing a stable self-concept than do people who were born blind. The
attitudes of the sighted towards the visually impaired, rather than those of
the visually impaired toward themselves, is often an important factor in a healthy
self- concept. These people are regarded by society as partially sighted sometimes,
and at other times blind. These conflicting identities hamper the growth of
a healthy self-concept. The partially sighted person requires time to form an
adaptive self-concept, and often has trouble doing so.
Vision loss will also disrupt established patterns of communication, motility,
work, recreation, and other aspects of self awareness. Typical reactions are
first shock, and then depression. The shock phase usually lasts from two to
seven days, with profound feelings of depersonalization, total immobility, and
blank facial expressions. This depersonalization is an emerging defense due
to the overwhelmingly painful reality of vision loss.
Little by little these feelings are confronted which marks the beginning of
the second stage. Symptoms of depression gradually emerge and blend with the
feelings of depersonalization. This is basically a "mourning time" for the loss
of sight. The mourning process is natural, and the person should be allowed
to go through this phase before they can begin to deal with such things as mobility
training and learning other functional tasks(15).
The recovery phase is characterized by a healthy resolution of the work of the
"mourning process". Energy is then directed to finding solutions. Re-education,
motility, learning new ways to communicate, and acceptance of the vision loss
as a handicap rather than submit to it, will then take place.
Mobility
Regardless of the age at which the vision loss occurs, the restrictions it imposes
on movement of all kinds is frustrating for the person affected. All of the
things that at one time were unconsciously done are now a source of anxiety.
The partially sighted individual must now learn new ways to navigate, lacking
the visual clues upon which they have previously relied on. This can be accomplished
through "mobility training", which teaches the person to use canes, electronic
aids, and low-vision devices to facilitate movement and travel. This training
also includes the use of public transportation because the options of driving
a car, or even riding a bicycle, are no longer possible(16).
Until the difficulty of mobility is overcome, the partially sighted individual
will not feel a sense of independence. This is often a very stressful time because
extensive training is necessary just to learn how to use the long-cane properly.
New routines must be established and old ones adapted. It is very hard for a
person to "feel" independent when they can't even go to the grocery store by
themselves because they need someone else to drive them there.
Services Available
The Lighthouse, founded in 1906, is the largest nonprofit agency in the country
serving the visually impaired and blind individuals. The Westchester Lighthouse
was formed in 1961 and provides service to over 1,100 people annually. Ninety
percent of these people are visually impaired and ten percent are totally blind.
All the programs and services are community based, and offered in a persons
home, school or place of business. There are no age limitations or income eligibility
required to obtain services that are provided by staff who are professionally
trained and certified. The goal of the Lighthouse services are to maximize the
consumers ability to function independently.
The Lighthouse offers almost 50 service programs that include:
1).Social Work and Counseling
2).Rehabilitation Teaching
3).Low Vision Clinical Care
4).Mobility Instruction
5).Support Groups
6).Technology Center
7).Job Placement Assistance
8).PublicInformation
They also provide low vision products such as "talking" clocks and calculators,
which can be ordered from a catalog. They are also involved in psychosocial
and laboratory vision research.
The National Association for the Visually Handicapped, focuses their services
on providing large-print books and reading material for the visually impaired.
The R.P. Foundation, formed in 1971, is a national eye research foundation dedicated
to finding a cure for R.P. and other retinal degenerative diseases. The R.P.
Foundation funds more research on these diseases than any nongovernmental agency
in the world, supporting basic and clinical research projects in both the U.S.
and foreign countries. The R.P. Foundation has more than 50 affiliates in the
U.S. and in 20 foreign countries. Approximately 80% of its budget is spent on
research, public health and education and human services(17).
The R.P. Foundation also sponsors a Retina Donor Program for those who have
inherited retinal degenerative diseases and their families. This program was
established in 1982 in response to the need for researchers to study diseased
human retinal tissue.
In 1988, the R.P. Foundation established a computerized National Registry to
identify and collect medical and family histories on all the people in the U.S.
with retinal degenerative diseases. A Newsletter is also published to inform
the public, supporters and affected people about recent research developments,
and other important information.
The individual affiliates also have support groups that help people deal with
the emotional and physical aspects of vision loss.
Outlook For The Future
There is unfortunately no cure or treatment for Retinitis Pigmentosa, so the
first step is to discover the genetic cause. Once these genes are identified,
researchers can then begin to determine how they function, and what role they
play in R.P. and normal vision.
As of today, two genes have been located that cause a form of autosomal dominant
R.P., one on chromosome 3, and the other on the short arm of chromosome 8. There
are no known retina genes mapped to chromosome 8 and researchers are now trying
to find the RP gene on the rest of the chromosome. Once this gene is found,
it can be isolated and then studied to discover its functions. This gene has
a role in normal vision, and when altered, as in people with R.P., leads to
retinal degeneration(18).
Another recent development has taken place in a technique to successfully transplant
retinal epithelium. A team of researchers at the RP Center are currently testing
this technique on rats that are blind due to a defect in the retinal epithelium.
This may lead to a way to replace defective retinal epithelium with healthy
epithelium(19).
A six-year, $5 million dollar study was conducted at the Berman-Gund Laboratory
for the Study of Retinal Degenerations of Harvard Medical School with funding
by the R.P. Foundation and National Eye Institute, National Institutes of Health.
The study concludes that most adult patients with R.P should take 15,000 IU
of vitamin A daily and avoid high doses of vitamin E. Although this is not a
cure, it has proven to have an influence on the progression of the disease,
and has the potential to add many years of useful vision(20).
The use of vitamin A is a first step in managing R.P. for some people, but the
search for causes, prevention, and cures for R.P. and all related diseases needs
to continue. Knowledge of the underlying causes of R.P. that emerge from the
clinical studies and genetic research, combined with an increasingly diverse
understanding of the biology and bio- chemistry of the eye, will hopefully lead
to prevention, treatment and a cure for all retinal degenerative disorders.
WORKS CITED
1.Kirtly,Donald. The Psychology of Blindness.Chicago; Nelson-Hall,1975.
2.Faye,Eleanor. The Low Vision Patient. New York; Grune & Stratton,1970.
3.Dobree,J.& Boulter,E. Blindness and Visual Handicap. N.Y. Oxford University
Press,1982.
4.IBID
5.R.P. Foundation Fact Sheet
6.Sardegna,J.& Paul,T. Encyclopedia of Blindness & Visual Impairment.N.Y.;Facts
on File,1991.
7.R.P. Foundation Newsletter; Spring 1986
8.Encyclopedia of Blindness & Visual Impairment
9.Ludman,M.& Wynbrandt,J. Encyclopedia of Genetic Disorders And Birth Defects.N.Y.;Facts
on File,1991.
10.R.P. Foundation;Information obtained by phone
11.Encyclopedia of Blindness and Visual Impairment
12.Randall,J.)Understand: Low Vision.N.Y.;A.F.B..1983
13.IBID
14.IBID
15.The Psychology of Blindness
16.Blindness & Visual Handicap
17.R.P. Pamphlet
18-R.P. Newsletter; Fall,1991
19.R.P. Newsletter;Spring,1986
20.R.P. Newsletter; Summer,1993
Send comments to rpmail@jwen.com