– Ed

Retinitis pigmentosa (RP) is a group of rare, genetic disorders that involve a breakdown and loss of cells in the retina — which is the light sensitive tissue that lines the back of the eye. Common symptoms include difficulty seeing at night and a loss of side (peripheral) vision.
How common is RP?
RP is considered a rare disorder. Although current statistics are not available, it is generally estimated that the disorder affects roughly 1
in 4,000 people, both in the United States and worldwide.
What causes RP?
RP is an inherited disorder that results from harmful changes in any one of more than fifty genes. These genes carry the instructions for making proteins that are needed in cells within the retina, called photoreceptors. Some of the changes, or mutations, within genes are so severe that the gene cannot make the required protein, limiting the cell’s function. Other mutations produce a protein that is toxic to the cell. Still other mutations lead to an abnormal protein that doesn’t function properly. In all three cases, the result is damage to the photoreceptors.

What are photoreceptors?
Photoreceptors are cells in the retina that begin the process of seeing. They absorb and convert light into electrical signals. These signals are sent to other cells in the retina and ultimately through the optic nerve to the brain where they are processed into the images we see. There are two general types of photoreceptors, called rods and cones. Rods are in the outer regions of the retina, and allow us to see in dim and dark light. Cones reside mostly in the central portion of the retina, and allow us to perceive fine visual detail
and colour.
How is RP inherited?
To understand how RP is inherited, it’s important to know a little more about genes and how they are passed from parent to child. Genes are bundled together on structures called chromosomes. Each cell in your body contains 23 pairs of chromosomes. One copy of each chromosome is passed by a parent at conception through egg and sperm cells. The X and Y chromosomes, known as sex chromosomes, determine whether a person is born female (XX) or male (XY). The 22 other paired chromosomes, called autosomes, contain the vast majority of genes that determine non-sex traits.
Autosomal recessive inheritance
In autosomal recessive inheritance, it takes two copies of the mutant gene to give rise to the disorder. An individual with a recessive gene mutation is known as a carrier. When two carriers have a child, there is a:
- 1 in 4 chance the child will have the disorder
- 1 in 2 chance the child will be a carrier
- 1 in 4 chance the child will neither have the disorder nor be a carrier
What are the symptoms of RP?
In the early stages of RP, rods are more severely affected than cones. As the rods die, people experience night blindness and a progressive loss of the visual field, the area of space that is visible at a given instant without moving the eyes. The loss of rods eventually leads to a breakdown and loss of cones. In the late stages of RP, as cones die, people tend to lose more of the visual field, developing tunnel vision. They may have difficulty performing essential tasks of daily living such as reading, driving, walking without assistance, or recognising faces and objects.

How does RP progress?
The symptoms of RP typically appear in childhood. Children often have difficulty getting around in the dark. It can also take abnormally long periods of time to adjust to changes in lighting. As their visual field becomes restricted, patients often trip over things and appear clumsy. People with RP often find bright lights uncomfortable, a condition known as photophobia. Because there are many gene mutations that cause the disorder, its progression can differ greatly from person to person. Some people retain central vision and a restricted visual field into their fifties, while others experience significant vision loss in early adulthood. Eventually, most individuals with RP will lose most of their sight.
How is RP diagnosed?
RP is diagnosed in part through an examination of the retina. An Eye Care Professional will use an ophthalmoscope, a tool that allows for a clear view of the retina. This typically reveals abnormal, dark pigment deposits that streak the retina. Visual field testing can also confirm the diagnoses.
What’s the treatment for RP?
Currently there is no effective treatment protocol for RP. Over time, RP will lead to blindness. Once diagnosed, it is important to prepare the patient for the future and consider the best career choice that will be most suited for a blind person.