What is retinitis pigmentosa?

01 April 2021

Author: Kate Green

what is retinitis pigmentosa

Understanding retinitis pigmentosa

 

Retinitis pigmentosa (RP) is a group of inherited eye diseases which affect the retina – the back of your eye that is light sensitive, allowing you to see. The retina is made up of photoreceptor cells which detect light and colour, called rods and cones. There are around 100 million rods in your retina, and between 6 and 7 million cones. Rods detect light and dark but cannot distinguish between different colours. Your cones are responsible for colour vision and perceive either red, green or blue shades.

 

RP causes your photoreceptor cells to break down and die, causing vision loss which gets progressively worse over a number of years. Most forms of RP affect your rod cells first, meaning that you usually begin to suffer with night blindness as your eyes struggle to adjust between dark and light environments. A person with normal vision is usually fully adjusted to a dark environment between 15-30 minutes after entering it, while it takes a person with RP much longer – or it doesn’t happen at all. Your peripheral vision is also one of the first things affected by the onset of RP. People with less common forms of RP begin to experience changes in their colour vision first as their cone cells are affected before their rod cells. They are also likely to lose their central vision first too.

 

RP typically first presents in children from the age of 10 onwards, often coming on strongly during adolescence. As a young person with RP ages, more and more of their vision will be affected and gradually lost over the years. By the age of 40, people with RP are usually legally blind. They may still have some central vision or light perception but not enough for them to safely drive or easily navigate daily life. RP affects around 1 in 4,000 people in the UK. Typically, half of people who have the condition also have a family member with it, but those who don’t know a family member with it will likely know a carrier of the RP gene instead. Carriers can pass on the gene without suffering from RP themselves.

 

What are the symptoms of retinitis pigmentosa?

 

There are several symptoms of RP which might indicate the early stages of the condition:

  • Night blindness
  • Losing peripheral vision
  • Difficulty seeing fine detail
  • Changes to colour vision
  • Light sensitivity

 

Everyone suffers differently with RP and some people might lose more vision than others over the course of their lifetime. The changes can also happen very irregularly with a rapid loss of vision over a short period of time and no further changes for several months or years after that, before the next cluster of deterioration. While you will likely lose your peripheral vision early on, lots of people with RP still have central vision into their 50s or 60s. In fact, many patients with retinitis pigmentosa retain a small degree of central vision throughout their life.

 

What are the causes of retinitis pigmentosa?

 

RP is an inherited condition and is caused by a recessive gene which must (in the majority of RP cases) be inherited from both parents to cause RP. A parent that has the gene has a 50% chance of passing it onto their child. People can carry the gene for RP without suffering from it themselves. In fact, there are over 60 different genes which cause a range of types of RP.

 

You can inherit RP in 3 different ways (sourced from RNIB).

“Autosomal dominant. To have autosomal dominant RP, you only need one faulty gene to have the condition. This can be inherited from either of your parents. Usually this parent will also have RP. If you have autosomal dominant RP, there is a 50% risk of passing it on to each of your children.

Autosomal recessive. Autosomal recessive RP requires two faulty genes, one inherited from each of your parents. If both your parents have one normal gene and one faulty gene, their vision will be unaffected but they will carry the gene for RP. If both your parents pass on their faulty RP gene to you, you will inherit autosomal recessive RP. With this condition, you will pass on a faulty gene to all your children. If they inherit a normal copy of the gene from their other parent, they will be carriers of RP. 

 X-linked. Men have one X and one Y chromosome while women have two X chromosomes. The gene relating to X-linked RP is found on an X chromosome. This means men with a faulty gene on their X chromosome will have the condition. If a woman has a faulty gene on one X chromosome but a normal gene on the other, she is usually more mildly affected or does not have any symptoms from the condition at all. This means she is a carrier of the condition. A man with X-linked RP will pass on the faulty gene to all his daughters but not to his sons. His daughters will be carriers of the condition but his sons won’t be affected.”

 

The RNIB have a wealth of resources relating to loss of vision and can provide support and guidance to those who feel they may be suffering with retinitis pigmentosa, or another visual condition. If you feel this may be you, visit the RNIB’s site for further information.

 

How can you diagnose retinitis pigmentosa?

 

If you are in your teens or twenties and have noticed your vision changing, it’s important to go and get your eyes checked. These symptoms might include changes to your peripheral vision, colour vision or central vision. The optometrist will conduct a visual field test, which will assess your peripheral vision with a series of lights or shapes shown to the side of you. You will need to let the optometrist know when you can see them, allowing a map to be drawn of your current vision and exactly how much you can see.

 

It is likely that there will also be some colour vision tests conducted to assess the state of your cone cells, in the instance that they are affected by RP before your rod cells. Alongside this, you might also undergo retinal checks. For this, the ophthalmologist will use an ophthalmoscope to look at the back of your eye closely. People who have RP have clumps of dark pigment around the retina, so this test is often used to confirm that a person has RP.

 

Once it has been established that you have RP, you can actually submit a DNA sample to identify which type of RP you have. This can also provide answers as to who in your family is a carrier of the gene, giving further clues as to which future generations might also be affected by the condition.

 

How can you treat retinitis pigmentosa?

 

Unfortunately, there is no cure for RP yet and once you’ve lost vision to the condition, there isn’t a way to regain it. However, there is more research into RP treatments all the time including taking a high dose of vitamin A palmitate, which is thought to slow the progression of further RP. Your doctor may also recommend wearing sunglasses when outside as these can reduce your light sensitivity symptoms and prevent UV rays from entering your eyes. UV rays are thought to speed the process of RP along, so taking any steps you can to mitigate their effect is important.

 

There are also several treatments which are currently under review, including retinal cell and tissue replacement, and gene therapy to place healthy genes into your retina. These treatment options are not available yet to wider groups of RP patients, but they are a step in the right direction and provide hope and potential avenues to explore for future treatments.


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