Definition

Retinitis pigmentosa (RP) is a group of inherited eye diseases that often leads to severe visual problems. The retina is a layer of light-sensitive tissue that lines the back of the eye. It converts visual images that we see into nerve impulses that it sends to the brain. Some types of RP are associated with other inherited conditions. This disorder is named for the irregular clumps of black pigment that usually occur in the retina with this disease.

Causes

Many types of RP are caused by a genetic mutation. Some cases occur sporadically.

Vision loss occurs when light-sensitive cells in the retina gradually break down. There are two types of cells in the retina:

• Cones—These cells are found mostly in the center of the retina. Cones are needed for central vision and to see colors.
• Rods—Located mostly away from the center, rods respond to dim light. They provide night and peripheral vision.

In most forms of retinitis pigmentosa, the rods die. Vision, thus, becomes impaired at night. The ability to see things off to the side while looking ahead also decreases.

In some forms of RP, the cones are lost. In those cases, central and color vision suffers. Vision loss usually progresses over a period of many years.

Risk Factors

RP is more common in males and in those with family members who have it.

Symptoms

Reduction of vision is usually first noted in childhood or early adulthood. The disease gradually worsens. After a number of years, vision loss may become severe.

Symptoms vary, depending on the type of retinal cell that is affected. Both eyes often experience similar vision loss.

It should be noted that RP is a slowly progressive disease over many years and that most people never become completely blind. In fact, even though many people with RP are considered “legally blind,” it is only because they have very constricted fields of vision (poor peripheral vision). Some still maintain excellent central visual acuity.

In general, RP may cause:

• Night blindness (the most common symptom)
• Eyes take longer to adjust to dim lighting or are slow to make adjustment from bright sun to indoor lighting
• Trouble seeing in foggy or rainy weather
• Decreased peripheral vision/visual field narrows, often called “tunnel vision”
• Difficulty seeing colors, especially blue
• Visual loss, partial or complete, usually gradually progressive
• Clumsiness from lack of sight, especially in narrow spaces such as doorways

Blurry vision from cataracts may complicate RP later in the disease.

Diagnosis

Your doctor will ask about your symptoms and medical history, and perform an eye exam. You may be referred to an eye specialist for further treatment.

Vision tests may include:

• Visual field testing—To check peripheral vision, which is how well you see off to your side, rather than directly ahead, without moving your eyes.
• Visual acuity—Checks how well you can see progressively smaller objects, usually a row of letters or numbers.
• Dark adaptometry—Tests how your vision adapts to darkness.
• Color testing—Tetermines how well you can differentiate colors.
• Electroretinogram (ERG)—A test to measure electrical activity in the eye. This test identifies the loss of cell function in the retina and is used to track progression of the disease.

Treatment

There is no effective treatment or cure for RP. Treatment aims 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 RP you have. Recommendations include:

These may include the following:

• Magnifying glasses
• Electronic magnifiers, which project an enlarged image onto a screen
• Night vision scopes, which enlarge distant objects under conditions of low light
• Lenses for distant vision (eyeglasses or contacts)

Some community organizations offer classes to help people with vision loss adjust and learn how to use vision aids. If you are considered legally blind, you are entitled to many low-vision services at no cost.

You should avoid taking sildenafil. Ask your doctor if there are other medications you should not take.

Prevention

Once RP has been inherited there are no known ways to prevent the disorder from occurring. If you have RP or have a family history of the disorder, you can talk to a genetic counselor when deciding to have children.

RP International http://www.rpinternational.org/

The Canadian National Institute for the Blind http://www.cnib.ca

The Foundation of the American Academy of Ophthalmology. Retina and Vitreous, Basic and Clinical Science Course. 2001-2002.

Harrison’s Principles of Internal Medicine. 14th ed. The McGraw-Hill Companies; 2000.

Ophthalmology. Mosby International Ltd; 1999.