Retinitis Pigmentosa

What is retinitis pigmentosa?

Retinitis pigmentosa refers to a group of diseases that affect the retina. The retina is the delicate innermost layer of tissue that lines the eye. It contains layers of light receiving cells called photoreceptors that are connected to the brain by the optic nerve. If you think of the eye as a camera receiving images, then the retina is the film on which those images are recorded. Beneath the retina is the retinal pigmented epithelium (RPE). The RPE supports the function of photoreceptor cells in the retina.

There are two types of photoreceptor cells in the retina: cone cells and rod cells. Cone cells are concentrated in the center of the retina (called the macula), and are responsible for central and color vision. Rod cells are outside the macula and are required for peripheral vision and for night vision. Both cone and rod cells convert light into electrical impulses which travel through several types of nerve cells to the optic nerve, which then carries the signal to the brain, where "seeing" actually occurs. With RP, photoreceptor cells begin to degenerate and eventually stop functioning.

What causes retinitis pigmentosa?

The basic cause of retinitis pigmentosa is thought to be genetic. The disease is programmed into your cells and not caused by injury, infection or any other external agent. Genetic defects, or mutations, give faulty messages to the retinal cells, leading to their progressive degeneration. This in turn, leads to vision loss.

How is RP inherited?

Genetics is a complex subject, and The Foundation Fighting Blindness has prepared a booklet, "The Inheritance of Retinal Degenerations," to explain this topic in detail. There are so many different forms of RP, which fall within one of three standard inheritance patterns.

Each type of inheritance will create a different pattern of affected and unaffected family members. For example, unaffected parents could have affected children, and affected parents could have both affected and unaffected children. In some families, only males will be affected, while females will carry the trait but not typically exhibit it. There are also isolated cases in which one individual appears to be the only member of a family to have a retinal degeneration.

A gene for RP can be either autosomal dominant, autosomal recessive, or X-linked. Autosomal means that the gene is attached to one of the 22 pairs of chromosomes that are the same in males and females; X-linked (formerly referred to as sex linked) means that the gene is carried only on the X chromosome, which is one of the two chromosomes that help determine the sex of a child. If the gene is dominant, only one parent need have it for a child to be affected; if the gene is recessive, the disease can only show up in a child if both parents are carriers of the mutant gene; if it is X-linked, only males will be affected while females will be carriers of the gene but not typically experience serious vision loss themselves.

It is important to remember that because RP is an inherited disorder, it commonly affects other members of a family. If someone in your family is diagnosed with a retinal degeneration, it is strongly advised that all members of the family contact an eye care professional.

How common are inherited retinal degenerations?

Retinal degenerations affect men and women of all ages, races, cultures, and ethnic backgrounds. The broad range of retinal degenerative diseases affects at least six million Americans.

Approximately 100,000 people in the United States are affected by retinitis pigmentosa or Usher syndrome, which is a variation of RP that also impairs hearing. It is estimated that one of every 80 people carries a recessive gene for RP, although this does not mean they or their children will necessarily have the disease. Approximately six million Americans are diagnosed with age-related macular degeneration, a disease that causes a loss of central vision. In addition, there are a number of less common forms of retinal degeneration.

What are the odds that I will pass the RP gene on to my children?

"Deciding whether or not to have children is a personal decision that everyone with RP has to make, and it is not an easy one," says Diane Ryan, who has RP. Although she did not know her own diagnosis until after her children were born, she has shared her sons' struggles with the decision of whether to take the risk of passing an RP gene to their offspring.

You can get the best information about the likely inheritance pattern of the disease in your own family by consulting with a genetic counselor or eye care professional who specializes in hereditary retinal degenerations. They can help you learn how the disease is inherited in your family and the chance of passing it on to your children.

Most of the Research Centers receiving support from The Foundation Fighting Blindness provide genetic counseling as part of their diagnostic evaluation. The Foundation can also provide a list of genetic counseling information services. If you would like to receive this material, please contact The Foundation's Constituent Service office.

What are the symptoms of RP?

Tom Tarrant: "I don't ever remember seeing in the dark. I just don't know what that's like. I remember Halloween when I was a little boy, walking into poles."

RP symptoms can vary. In a person with classic or typical RP, night vision and peripheral (or side) vision will be affected initially. Night blindness is one of the earliest and most frequent symptoms of RP, and it refers to difficulty seeing not only at night but also in dimly lit places, such as restaurants and movie theaters. The loss of peripheral vision is often called "tunnel vision." If you imagine peering down a tunnel, able only to see what is in front of you and nothing to the side, this is what it is like to lose peripheral vision. As vision loss progresses, the "tunnel" becomes more and more narrow. In the later stages, some patients may also lose central vision.

Some cases of RP do not follow the classic symptoms of the disease. These patients may instead first experience some loss of central vision and color perception followed by night blindness.

What is common to all cases of RP is the progressive nature of the disease. When symptoms first appear they may be virtually imperceptible, particularly in an individual who is not aware of a family history of RP and thus not as observant of symptoms as an individual who has watched the disease develop in other family members. But symptoms may progress at different rates even in members of the same family. Once one adjusts to low vision, further adjustments will likely be necessary as the progression continues.

How and when can RP be diagnosed?

"I was diagnosed at 14 years old and before that I always remember not being able to see at night and being 'klutzy'," remembers Rob Lee. "I was bad at soccer and basketball and didn't know why. I figured that I saw the way everyone else did, but just wasn't as good as others. Being diagnosed with RP was somewhat of a relief to me because it gave me a reason why I couldn't do certain things and why I was a little different from my friends and brothers."

Many people with RP, especially older people, tell stories of the difficulty they experienced in getting an accurate diagnosis of their condition. Increasingly sophisticated diagnostic technology and growing awareness among physicians is helping to make situations like this less common. RP is usually diagnosed in young adulthood, although certain forms of RP are evident in early childhood and other forms may not appear until later in life.

Are there specialized tests and instruments to look for RP?

Tests can definitively diagnose RP. There are two basic categories: those that are psychophysically based, and those that are electrophysiologically based.

Each test has a specific function, and it may not be necessary for your doctor to use all of the tests described here to test your vision. If you have questions about why your doctor is or isn't performing a certain test or using a certain instrument, it is important that you ask your doctor to explain. Never be afraid to ask your doctor why he or she is doing something. Your doctor appreciates an informed patient and will be happy to answer your questions.

Psychophysical testing is likely to be done at some time during your diagnosis. These tests include:

• Acuity tests which measure the accuracy of your central vision at specific distances in specific lighting situations. This is the psychophysical test that people are most familiar with and typically involves a standard eye chart.
• Color testing which can help determine the status of your cone cells. Since cone cells are the retinal cells that interpret color, your doctor will be better able to determine the health of these cells through your performance on these tests. There are several types of color tests which measure various aspects of vision.
• A visual field test uses a machine to measure how much peripheral vision you have. Often this test is conducted with a computerized piece of equipment that maps your visual field (the area you can see) and can provide a more detailed definition of your vision loss.
• A dark adaptation test which will measure how well your eyes adjust to changes in lighting. Information from this test can help the doctor to better understand the current function of your rod cells, which are the retinal cells responsible for night vision.
• Photos are often used to record the changes in your retina that occur as a result of RP and are used to compare these changes over a period of time. Fundus photos, as they are typically called, are taken of the back of your eye (the word "fundusquot; means farthest to the back).

The electrophysiological test used most frequently is called an electroretinogram or ERG. The ERG records the electrical currents that are produced in the retina by a light stimulus. In healthy photoreceptors, there is a characteristic intensity and speed of the electrical signal, which becomes reduced as photoreceptor cells degenerate.

To administer an ERG test, the patient sits in a very dark room to adjust their eyes to the dark. Once their eyes are adjusted, the technician places a double patch on one eye and administers eye drops and a contact lens in the other. The ERG machine flashes bright lights at the eye with the contact lens and records the way the photoreceptor cells in the eye respond to the light, both eyes are tested the same way. Although patients report discomfort from the flashing lights, ERG testing is a very valuable diagnostic tool.

How quickly does RP progress?

"Every year I lose a little bit of vision, and every year I do some adjusting," notes Tom Tarrant, who describes himself as "still having a lot of useable vision," although he is legally blind.

While gradual vision loss is the common feature of almost all forms of RP, there is no predictable rate of loss, even for people in the same family. Usually the progression is quite slow. Vision sometimes appears to remain stable between annual eye examinations.

Does exposure to light affect loss of vision in people with RP?

There is no scientific evidence that normal levels of light increase vision loss. People with RP may use their eyes in ordinary light without restriction. Many people with RP find they are more comfortable avoiding bright lights and bright sunlight. As a precaution, people with RP and other retinal degenerations are encouraged to protect their eyes from long-term exposure to bright sunlight until more is known about this subject. Good quality sunglasses are recommended for bright days.

Aside from the gradual progressive loss of vision, can a person with RP seem to have better and worse vision at different times?

Yes, this is often the case. A number of factors might account for good days or bad days for someone with RP. For example, some people feel they see better on cloudy days; others feel they do not see as well on cloudy days. Fatigue and emotional stress may also temporarily affect vision. People who have RP report that it often takes a lot of effort to see and that the emotional and physical effort is exhausting and makes one feel as if they don't see as well when they are tired. However, none of these circumstances seem to affect the progression of RP.

What about cataracts and RP?

It is not unusual for an individual with RP to develop a cataract, which is a clouding of the lens of the eye. Cataracts that significantly interfere with vision can be surgically removed. While cataract surgery cannot improve vision loss due to retinal degeneration, it can lessen the vision loss caused by the cataract. Because surgery is not advised for everyone, it is important to discuss the details of your individual case with an eye care professional that is familiar with retinal degenerations.

What is Cystoid Macular Edema?

Cystoid macular edema is a well-recognized complication associated with RP. It is thought to occur in about fifty percent of RP cases at some stage in the disease. Cystoid macular edema causes a build up of fluid in the macula. The macula is the central portion of the retina responsible for perceiving fine visual detail. Some, but not all, patients who develop cystoid macular edema will experience a reduction of their central vision. Ophthalmologists can treat this complication with a drug called acetazolamide, known under the brand name Diamox. Only about half of those treated with Diamox will respond to therapy. Cystoid macular edema can also sometimes spontaneously clear. If you notice a decrease in your central vision, see your ophthalmologist immediately. It is also a good idea for patients with RP to have regular eye examinations.

Can RP lead to total blindness?

Blindness, to most people, means a complete loss of sight. As they grow older, some people with RP do become blind in this sense. However, many will retain a small amount of vision such as light perception.

A majority of people with RP are legally blind by the age of 40. People who are legally blind usually maintain a good deal of functional vision supplemented by adaptive technology. Legally blind individuals are those whose best visual sharpness or acuity (with glasses or contact lenses, if needed) is 20/200 or worse in their better eye; or whose visual field, regardless of acuity, is restricted to a 20 degree diameter (10 degree radius).

Is there a treatment for RP? Is there any way to keep it from getting worse?

While researchers are gaining new understandings about the precise genetic causes of RP and the actual mechanisms of the disease, so far research has not found a way to halt the degeneration of the retina or to restore lost vision. However, research is continuing in several different areas that offer hope for people with RP.

Among the most exciting recent findings were the results of a six-year clinical study reported in June 1993 concerning vitamin A palmitate and RP. Researchers wanted to determine if increasing the amount of vitamin A palmitate in the diet could slow the progression of retinal degeneration.

Patients with a daily consumption of about 18,000 International Units (IU) of vitamin A (15,000 IU of vitamin A palmitate in dietary supplements and about 3,000 from their regular diet) were found to have a slower progression of retinal degeneration, as measured by ERG, than patients not taking these doses of vitamin A. Taking vitamin A palmitate did not completely stop retinal degeneration, but the researchers found a 20 percent slower average annual decline of remaining retinal function in people taking the supplement. They concluded that the slowing could mean additional years of useful vision for many people with RP. For example, a person starting the daily supplement at age 32 could expect to retain some useful vision until the age of 70, while a person not taking the supplement would lose useful vision by age 63.

However, there are some warnings that accompany this recommendation. There is no evidence that doses higher than 15,000 IUs provide greater benefits, and doses over 25,000 IUs daily may be toxic and cause side effects such as liver disease. While there are no reported instances of toxicity in healthy adults taking 15,000 IU of vitamin A palmitate daily, people taking the supplement are advised to have a test of their liver function and have their blood levels of vitamin A measured before they begin the regimen, and annual tests thereafter. Also, because of the potential for birth defects, women who are pregnant or planning to become pregnant are not advised to take vitamin A palmitate in this dosage. And this recommendation is for adults; RP patients under the age of 18 were not evaluated and 15,000 IU of supplementary vitamin A palmitate is not recommended for children. Parents of children with RP should consult with their eye care professional and pediatrician about therapeutic doses of vitamin A palmitate for children, based on age and body size.

It is important to keep these findings in perspective. Vitamin A palmitate will not cure RP. Vitamin A palmitate will not improve your vision. The degenerative process will continue, but possibly at a slower rate. People with very advanced RP were not included in this study, and if you have advanced RP you should consult with your eye care professional about the possible benefit of vitamin A palmitate for you.

The same study that found these encouraging results from taking vitamin A palmitate supplements also looked at the effect of vitamin E supplements on retinal degeneration. In the case of vitamin E, the opposite effect was found. People taking 400 IU daily of vitamin E were found to have a faster rate of retinal degeneration than those in the other groups. This led to the recommendation that people with RP should avoid high dose vitamin E supplements. However, there is no evidence that normal dietary or small supplemental amounts of vitamin E have an adverse effect on the progression of RP.

In September 2004, a study was...

What about reports publicizing interventions that supposedly "cure" RP?

Over the years, practitioners have offered various unproven therapies for the treatment of blindness. Practitioners of unproven therapies are often well-intentioned people who want to help patients. However, without prior testing in carefully controlled clinical trials, patients may be exposing themselves to treatments that could actually accelerate vision loss or cause harmful side effects. For example, the same clinical trial which found that vitamin A palmitate slowed the progression of RP also found that daily doses of 400 IUs of vitamin E accelerated vision loss. Prior to this study, vitamin E was believed by some to have a beneficial effect on RP.

For a number of years, doctors in Cuba have offered a surgical intervention for RP that they claim halts further vision loss and in some cases restores sight. However, the doctors in Cuba have never provided any study data to support their claims of efficacy and safety. German and Norwegian ophthalmologists have reported serious complications from this surgery such as double vision from restricted eye movement, extreme sensitivity to light and accelerated vision loss. Because the Cuban doctors have never submitted any findings, the number of patients who have experienced similar outcomes is unknown.

To determine whether this intervention had any therapeutic benefit, The Foundation funded a follow-up study of patients who had traveled to Cuba of their own free will to receive the Cuban intervention. The study found that the treatment did not halt progression of the disease and may have actually accelerated vision loss. The negative results of this study are in agreement with two other studies that also failed to find any benefit for the Cuban intervention for RP.

The evidence that vitamin E and the Cuban intervention actually have a deleterious effect on vision in patient with RP highlights the concern that undergoing an untested treatment may cause harm rather than good. For this reason, The Foundation cannot recommend any untested therapy.

Is RP associated with other diseases?

RP is sometimes associated with syndromes that also affect other parts of the body. Usher syndrome causes hearing loss and vision loss from RP. Although Bardet-Biedl syndrome can involve many part of the body, the defining features of this syndrome are extra fingers and/or toes (which are present at birth) and obesity. Other diseases have a retinal degeneration that is similar to RP. RP is thought to be a part of Leber congenital amaurosis (LCA) Patients with LCA are born with very little vision. In some cases, LCA is associated with central nervous system complications such as developmental delay, epilepsy and motor skill impairment. Choroideremia is a retinal degenerative disease that causes the choroid and the retina to degenerate. Information about these diseases and syndromes is available from The Foundation.

Adapted from the Foundation Fighting Blindness Website