Retinitis Pigmentosa is the name given to a group of degenerative and inherited eye disorders that cause severe visual impairments. It is a rare condition and affects about 1 in every 4,000 people.
Some types of retinitis pigmentosa lead to sight loss (which is generally slow and gradual), while others cause complete blindness. It usually affects both eyes, although the severity of the condition can vary between the eyes. It is highly uncommon for retinitis pigmentosa to occur in just one eye.
The condition produces harmful mutations found in any of around 100 genes that exist, to our current knowledge. These genes carry instructions for building proteins, crucial for cells within the retina. These cells are called photoreceptors and carry necessary instructions to make proteins that are required for the retina to function healthily.
Some of these mutations are so severe that the gene fails to produce enough protein, limiting the cell's function. In some cases, they can also produce proteins that are toxic to the cell.
Photoreceptor cells, also known as rods and cones, are cells in the retina. These retinal cells observe and convert light into electrical signals which travel through the optic nerve into the brain. The brain processes them into the images that we see.
When light enters the eye, it focuses on the central part of the retina called the macula. The macula contains a few million specialised photoreceptors - the cone cells. Cones allow us to see colour and perceive fine visual details.
Rods help us to see in dim light and darker environments. They sit in the outer regions of the retina (the peripheral retina).
The human retina has approximately 6 million cones and 120 million rods.
The first stages of retinitis pigmentosa affect the rods more severely than the cones. As the rods dilapidate, individuals will experience reduced visibility in darker light settings and possibly night blindness. In addition to this, they will experience a progressive loss of their immediate visual field.
Following the breakdown of the rods, the cones soon follow and in the later stages on retinitis pigmentosa, the cones die. When this happens, the eyes to lose more of their visual field and develop tunnel vision. As a result, people will have difficulty performing simple daily tasks like driving, reading, or recognising faces and objects.
Retinitis pigmentosa is genetically inherited from one generation to the next in different ways. Identifying how it was inherited will tell you the following:
- Who in your family has had the condition
- Roughly how severely your vision will alter
- The chances of the condition passing onto your offspring.
Molecular genetic testing can identify the mode of inheritance in a family. There are three different ways in which people inherit retinitis pigmentosa:
Autosomal dominant inheritance
Autosomal dominant retinitis pigmentosa affects men and women at the same rate. A recognised history of the condition can show within the family.
This type of retinitis pigmentosa is less severe than the other types. The initial signs and symptoms tend to appear in an individual around the age of 30.
Only one copy of the gene with a disorder causing mutation can produce the condition. When a parent has a dominant gene mutation, there is a 1-in-2 chance that any children will inherit this mutation.
Autosomal recessive inheritance
Similar to dominant inheritance, recessive inheritance also affects men and women at the same rate. The major difference is that there may be little or no history of the condition in the family’s history. The condition usually begins around the age of 30, but can also develop a little later.
X-linked inheritance
With this type of retinitis pigmentosa, females are the primary carriers of the faulty gene. Nevertheless, this pattern of inheritance predominantly affects men. Despite being the leading carriers, women rarely develop the condition. This type of retinitis pigmentosa severely affects vision and can result in inferior vision by the age of 40.
In some cases, there is no known relative in the family with the condition. Therefore, it may not be possible to trace which of the three types of inheritance is causing the condition. Genetic counselling will help you understand which type of retinitis pigmentosa you have. It is a free service on the NHS which you can be referred to by your GP or ophthalmologist.
Before being diagnosed with retinitis pigmentosa, it is vital to make your optometrist aware of its history in your family.
Your optometrist will carry out visual field testing to look at how your peripheral retina is functioning.
An ophthalmologist will carry out further tests should your optometrist find any signs of retinitis pigmentosa.
Numerous services can aid people with vision loss to maintain an independent way of living. Services include experts such as occupational therapists, orientation and mobility specialists, low vision therapists and more.
Expert help may include training on how to use a cane or guide dog to navigate effectively with limited vision
Children with retinitis pigmentosa may have lenses to enhance their central vision and widen their visual field. These lenses can also help to get rid of glare from bright lights.