Retinitis Pigmentosa (RP) is the name given to a group of hereditary diseases that affect the retina. The retina lies at the back of the eye and it acts like the film in a camera, receiving and processing everything you see. The retina is a delicate layer of cells which reacts to light and converts the light into neural messages and transmits these messages to the brain. In humans there are two types of light sensitive cells in the retina: rod cells and cone cells
What are Rods and Cones?
Rod cells pick up movement out of the corner of the eye and also, in a normal eye it is the rods that operate in poor light or at night. There are about 120 million rods in each eye and they are more numerous towards the outer edge of the retina. The cone cells give us colour vision and are responsible for fine focus vision used in writing and reading. There are not as many cones and they are more concentrated in the centre of the retina (the Macula).
What causes RP?
RP is caused by a breakdown in the function of initially of the rods. This in turn is caused by toxic or malfunctioning proteins that cause the death of the photoreceptors. Mistakes in our DNA, called mutations, are responsible for the production of these incorrect proteins. There are many different forms of RP and a precise diagnosis is required to understand the condition and to pursue genetic testing to identify the genetic mutation which may lead to therapy. It is now known that the rods produce a Cone Viability factor and as rod degeneration progresses Cone malfunction may also ensue. RP may also be part of a syndrome such as Usher Syndrome which is RP accompanied by hearing loss. There are other disorders similar to RP like Gyrate Atrophy, Choroideremia etc. The common feature is the degeneration of the retina and researchers have identified more than 160 different genetic mutations implicated in some form of RP.
What are the symptoms of RP?
One of the earliest symptoms of RP is difficulty seeing at night or in poor illumination. Other symptoms include slow light to dark adaption times and poor contrast vision. This inability to differentiate weak contrast often affects children in the classroom - reading from the blackboard or the overhead projector. This also accounts for difficulties in negotiating concrete or carpeted stairs without edge markings.
Loss of side or peripheral vision may start later in the condition but eventually leads to significant loss of the field resulting in "tunnel vision".
The age of onset of RP and the rate of degeneration is extremely variable even within a single family. Some genetic forms may progress more quickly than others but the correct supplements, good nutrition and a healthy lifestyle may help to slow the rate of degeneration.