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What is Retinitis Pigmentosa?

By September 22, 2017No Comments

blind-man

Retinitis Pigmentosa, also referred to as RP more commonly, is a rare genetic disorder that causes sight loss. It involves the breakdown of the cells located in the retina, which is the light sensitive tissue lining at the back of the eye.

It has been estimated that roughly 1 in 4,000 people worldwide are affected by this disorder.

What are the cause of RP?

diagram-of-eye

RP is most commonly inherited. It is a result of harmful changes taking place in any one of more than 50 genes. The genes carry a make up of instructions for making proteins which are vital within the cells of the retina, these are called photoreceptors. Unfortunately, some of the changes or mutations to the changes are so severe that the gene cannot make up the protein which is required, and consequentially limiting the cell’s ability to function properly.

In other cases, the mutations actually produce a protein that is toxic to these vital cells.

Other mutations lead to a protein that does not function correctly.

In all three of these cases, the damage is done to the photoreceptors.

What are photoreceptors?

Photoreceptors are the cells in the retina that begin the overall process of seeing. They absorb light, then convert it into electrical signals to further the process.

Those electrical signals are then sent to the other cells in the retina to then find their way through the optic nerve, then to the brain where they are processed into images.

There are two types of photoreceptors which are known as rods and cones. Rods are in the outer area of the retina.  They allow us to see well in dim and dark light. Cones can be found mostly in the central portion of the retina. The cones are what allows us to see fine visual detail and colour.

What are the symptoms of RP?

Usually, the onset of symptoms begins in childhood, but can range between the ages of 10 and 30. The symptoms can range widely between cases of RP, but usually it affects the peripheral (outer) vision with only a small number of cases finding the effect taking place upon their central vision. In most cases, people with RP experience Tunnel Vision – meaning that their central vision is all they have.

Since it is a progressive disorder, people can lose sections of their sight at different stages of life. Almost all people with RP will lose most or all of their sight later in life. However, this could be due to the natural sight loss that happens to anyone on top of this genetic severe sight loss.

How does having RP affect someone’s vision?

In the earlier stages of development of RP, the rods are more affected than the cones. The rods are basically broken down and “die”. As the rods are dying off, people with RP will start to experience night blindness initially, as well as progressive loss of the visual field. The loss of rods is what leads on to the loss and/or breakdown cones. When the cones start to die, the loss of the visual field becomes more severe which usually results in developing tunnel vision.

The sight loss will normally have an impact on carrying out daily tasks such as driving, reading and writing, walking in unfamiliar places with assistance, or recognising objects or faces.

How is RP diagnosed?

In part, RP is diagnosed through an examination done on the retina. A professional in eye care will look through an ophthalmoscope, which is a tool that will allow him or her to get a clearer and wider image of the retina. RP typically reveals itself by abnormal, dark pigment deposits that streak the retina. This is the reason for the name ‘Retinas Pigmentosa’.

The other tests to diagnose RP include:

  • Visual field testing – this is to determine the extent of the vision loss. The person being tested is asked to watch a spot of light that moves around directly in front of the head and to either side. When the person being tested sees the light he or she pushes a button. From this, the specialist can create a map of what the person can see and what they cannot in terms of their field of vision.
  • Electroretinogram (ERG) – this measures the electrical activity of the photoreceptor cells. It uses a contact lens with electrodes attached and a flash of light is sent directly to the retina, where the electrodes measure the rod and cone cell responses. People who have the disorder will have decreased electrical activity, which reflects the lesser functioning of the photoreceptors.
  • Genetic testing – In a small amount of cases, a DNA sample will be taken from the person to give a genetic diagnosis. This way, people can learn about their individual progression of their particular form of the disorder.

Is there a cure for RP?

At current, there is no cure for RP. However, there are a number of services that are available to help people who are living with sight loss.

For children with RP, there are low-vision aids that can help to maximise their existing vision. An example of this are special lenses that magnify central vision to expand their visual field.

In general, technology has moved on a lot in recent years and there is voiceover software on every smart phone and on laptops and computers. There is even voiceover software available on some ATM’s across the United Kingdom.

There is access to mobility training to help someone with significant sight loss find their way around somewhere, eventually without assistance. This could be used for finding your way around school, university, an office or the commute to any of these things. Cane’s and guide dogs are also used for ways to get around independently and are visual indicators for people to watch out for.

For help and support  as a blind or partially sighted person, visit the RP Fighting Blindness Group on Facebook or visit the RNIB website for more details.

See also: Life Insurance for Disabled People

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