Retinitis pigmentosa, or RP, is a term that describes a group of chronic and progressive inherited diseases that can take many forms. Retinitis pigmentosa affects more than 100,000 individuals in Canada and three million people worldwide. One in 80 has the retinitis gene, the most common form. Usher syndrome, which is associated with RP, affects approximately 1,000 people in Canada.
Retinitis pigmentosa affects the retina at the back of the eye, which consists of several thin layers of nerve cells (rods and cones). The cones that are especially present in the center of the retina are responsible for the vision of the details (the visual acuity) and the vision of the colors. The rods are concentrated at the mid-periphery and at the periphery of the retina and are responsible for detecting motions in our field of vision and night vision.
Retinitis pigmentosa is characterized by degeneration of rods and cones as well as abnormal pigmentation of the retina. There is then appearance of cobwebs on the retina. The result of this disease is the night blindness (at the beginning) then the restriction of the fields of vision (vision in tunnel). Night blindness means that the person can cope quite well with daytime vision, but as soon as it gets dark, vision becomes impossible. Entering a movie theater, for example, becomes a nightmare! The symptoms are more and more important as the years go by.
The symptoms of RP are more important in teenagers and young adults and the disease progresses throughout the life of the individual. The speed of progression and the importance of visual problems vary from person to person.
The researchers found the defective genes that cause some forms of RP, especially the one that is transmitted predominantly (about 20% of all cases).
The RP can be detected quite early by an electroretinogram (ERG), which is measured in the eye in much the same way that the electrocardiogram (ECG) measures the activities of the heart. Genetic counseling is important to prevent the onset of this disease in children, for example.
Recently, researchers have reported that vitamin A (15,000 IU) can help slow the progression of the disease in some people. But the disease is not cured. It also seems that vitamin E has a detrimental effect on RP: it would accelerate the course of the disease. These studies involved 600 individuals aged 18 to 49 years and lasted between 4-6 years.
(Source : Association des Optométristes du Québec)