Retinal Degenerative Diseases
Millions of people in North America suffer varying degrees of irreversible vision loss because they have an untreatable, degenerative eye disorder like retinitis pigmentosa (RP), which affects an estimated 1.5 million people worldwide, or age-related macular degeneration, which is the leading cause of vision loss in Canada and North America. Retinal degenerative diseases affect the delicate layer of tissue that lines the inside back of the eye. This part of the eye -- the retina - is essential for vision.Imagine the eye is like a camera. The shutter, like the iris of the eye, opens and closes to let in the right amount of light. The lens helps to focus light on the film. The retina is like film. Regardless of the perfection or quality of the rest of the camera, if the film is faulty, the developed pictures may be distorted, blurred or impossible to see.
This very large and diverse group of vision disorders affects young and old and people from many cultures, races and ethnicities. Age-related macular degeneration is distinguished by its prevalence in the senior population, and age is considered to be the major risk factor for developing this eye disease. The RP family is generally thought to be an inherited form of eye disease, even if a person who develops it has no previous family history of vision loss. The list of inherited retinal dystrophies (degenerations) is very long, but here are a few of the more common:
- Best disease (affects central vision at an early age)
- Choroideremia (affects males)
- Cone-rod dystrophy
- Congenital stationary night blindness
- Leber congenital amaurosis (RP at birth)
Quick Facts:
Retinitis Pigmentosa (RP)Retinitis pigmentosa (RP) is the name given to a family of eye diseases that cause gradual deterioration of the retina. The most common form of RP follows a progressive pattern: loss of night vision (nyctalopia), loss of side (peripheral) vision and finally, very restricted tunnel vision. In some cases blindness is the eventual outcome. This large group of eye diseases has many variations. For instance, sometimes central vision is lost first, along with the ability to see colours, fine details and to recognize faces.
If the retina is affected by retinitis pigmentosa, it cannot be replaced by artificial lenses, corrected with surgery or cured with drugs. The RP group of eye diseases affects about one person in 2,500.
More RP Facts
- RP is generally believed to be an inherited disease.
- Although you cannot "catch" RP, almost half of all cases occur in families where there is no history of the disease.
- RP is a leading cause of inherited blindness among individuals between the ages of six and 60.
- Although symptoms can occur at any age, RP is most commonly diagnosed in early adulthood.
- RP is a component of other complex disorders like Bardet-Biedl syndrome, Usher syndrome and Alström syndrome.
- Much of today's RP research focuses on the genetic causes of the disease, and of the more than 100 gene mutations believed to be responsible for the various forms of RP, half have been found.
- Canadian scientists have made significant contributions to RP research, and they rank among the world's foremost authorities in this area.
Usher Syndrome
Usher syndrome is an inherited family of disorders that involve hearing loss and visual impairment caused by RP. Usher syndrome is actually a family of disorders and is the major cause of deaf-blindness in the world.
Doctors have identified three general types of Usher syndrome.
- Type 1: Individuals with Usher syndrome type 1 are born profoundly deaf. Problems with balance are common because the inner ear is affected. The first symptoms of retinitis pigmentosa may become apparent in adolescence or early adulthood.
- Type 2: Individuals with Usher syndrome type II have moderate to severe hearing impairment at birth. The hearing loss does not progress. The symptoms of retinitis pigmentosa that impair visual function usually become apparent during adolescence or early adulthood.
- Type 3: In 1995 it was discovered that there is a third type of Usher syndrome. Individuals with type III have progressive hearing loss accompanied by gradually diminishing vision due to retinitis pigmentosa.
Age-Related Macular Degeneration (AMD)
Age-related macular degeneration (AMD) is an eye disease that affects a small, specific area of the retina called the macula. The macula gives us our clear, straight-ahead vision, as well as the ability to see colours, fine details and recognize faces. Although the causes of AMD are unknown, it is now believed that it may have a strong genetic component. It affects about 35 percent of the population over the age of 75 years, and about 10% of these individuals will suffer debilitating vision loss.
More AMD Facts
- It is estimated that 800,000 Canadians are affected by age-related macular degeneration (AMD)
- AMD is the leading cause of blindness in Canada, and accounts for approximately one-third of all cases of vision loss.
- The triggers that cause AMD are not known, but the loss of central vision is caused by the deterioration of the macula, a small portion of the retina.
- Early symptoms of AMD include distorted vision, particularly seeing straight lines as being bent or wavy, or having blind spots in the area of central vision.
- Advanced symptoms include the inability to distinguish colours, recognize faces or read print.
There are two types of AMD: wet and dry.
- The dry form of macular degeneration causes gradual loss of central vision and accounts for about 90 per cent of all cases. At this time there is no known treatment for dry AMD, although much scientific research is underway.
- The wet form of macular degeneration can cause sudden or rapid vision loss, and occurs in about 10 percent of all cases. At this time there are only a few interventions, such as laser treatment, and photodynamic therapy ("cool" laser with a drug treatment) that can help a few individuals affected by this disease.
Researchers are looking for genes that may contribute to the development of AMD. Other areas of interest include treatments such as laser, pharmaceuticals and combinations of light and drug therapy.
The Foundation Fighting Blindness is proud to have funded research that has led to these recent groundbreaking discoveries:
Dr. Ian M. MacDonald
University of Alberta
Screening test for choroideremia
Dr. Roderick McInnes
University of Toronto
Gene for cone-rod dystrophy
Dr. Torben Bech-Hansen
University of Calgary
Gene for incomplete X-linked congenital starionary night blindness
Gene for complete X-linked congenital stationary night blindness