Retinitis pigmentosa (RP) is an inherited, degenerative eye disease that causes severe vision impairment and blindness. Sufferers will experience one or more of the following symptoms:
Night blindness or nyctalopia;
Tunnel vision (no peripheral vision);
Peripheral vision (no central vision);
Aversion to glare;
Slow adjustment from dark to light environments and vice versa;
Blurring of vision;
Poor colour separation; and
The progress of RP is not consistent. Some people will exhibit symptoms from infancy, others may not notice symptoms until later in life. Generally, the later the onset, the more rapid is the deterioration in sight.
A form of retinal dystrophy, RP is caused by abnormalities of the photoreceptors (rods and cones) or the retinal pigment epithelium (RPE) of the retina leading to progressive sight loss. Affected individuals may experience defective light to dark, dark to light adaptation or nyctalopia (night blindness), as the result of the degeneration of the peripheral visual field (known as tunnel vision). Sometimes, central vision is lost first causing the person to look sidelong at objects.
The effect of RP is best illustrated by comparison to a television or computer screen. The pixels of light that form the image on the screen equate to the millions of light receptors on the retina of the eye. The fewer pixels on a screen, the less distinct will be the images it will display. Fewer than 10 percent of the light receptors in the eye receive the colored, high intensity light seen in bright light or daylight conditions. These receptors are located in the center of the circular retina. The remaining 90 percent of light receptors receive gray-scale, low intensity light used for low light and night vision and are located around the periphery of the retina. RP destroys light receptors from the outside inward, from the center outward, or in sporadic patches with a corresponding reduction in the efficiency of the eye to detect light. This degeneration is progressive and has no known cure as of June 2012.
The most challenging aspect of RP is that it is not stable. Sufferers must continually adapt to less and less sight and how that impacts their life, career and relationships. Another aspect is that RP sufferers do not look different. RP does not result in any outward effect on the eyes and so people with RP "do not look blind". Furthermore, though legally blind because of reduced field of vision or acuity, they may be able to see things that hold in their line of sight long enough (if bright enough) to comprehend e.g. see large or bright objects albeit indistinctly.