Retinitis Pigmentosa

Definition

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

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 – found in the center of the retina. Cones are needed for central vision and to see colors.
  • Rods – located away from the center. They respond to dim light. They provide night and peripheral vision.
In most forms of Retinitis Pigmentosa, the rods die. Vision 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 years.

Risk Factors

A risk factor is something that increases your chances of getting a disease or condition. Risk factors for RP include:
  • Family members with RP
  • Sex: Male
  • Having certain other inherited conditions, including:
    • Fanconis syndrome
    • Friedreichs ataxia
    • Olivopontocerebellar degeneration
    • Bassen-Kornzweig disease
    • Kearns-Sayre syndrome
    • Refsums disease

Symptoms

Loss 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 experience similar vision loss. Symptoms may include:
  • Night blindness (the most common symptom)
  • Eyes take longer to adjust to dim lighting
  • Trouble seeing in foggy or rainy weather
  • Eyes are slow to make adjustment from bright sun to indoor lighting
  • 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
  • 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, such as an ophthalmologist.
Vision tests may include:
  • Goldmann perimetry – 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.
  • Dark adaptometry – tests how your vision adapts to darkness.
  • Color testing – determines how well you can differentiate colors.
  • Electroretinogram (ERG) – identifies the loss of cell function in the retina. It is also used to track progression of the disease.

Treatment

There is no effective treatment or cure for Retinitis Pigmentosa. 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. Recommendations include:
Vitamin A – supplements of vitamin A may slow vision loss when taken over a long period. Immediate slowing of vision loss is not noticeable.
Low-vision aids – these 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 to adjust and to learn how to use vision aids.

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.