This thin layer of light-sensitive cells sends information on shape, colour, pattern and movement to the via the optic nerve. There are special light sensing cells in the retina, called rods and cones.
What is retinitis pigmentosa? (hereditary) diseases that damage the retinal rod and/or cone cells and cause vision to fade.
Inherited retinal diseases (IRD) affect approximately one in every 3,000 Americans. The severity of symptoms, speed of progression and age of onset varies from person to person. This can also differ between family members within the same family.
The retina contains millions of cells called rods and cones.
They are named this because of their appearance
Rods, found in greater numbers than cones, are located across the entire retinal surface. There is a higher concentration of rods around the periphery (edges) of the retina, which allows you to see what is above, below and to the sides of the object you are directly viewing.
One of the key functions of rods is to detect low light levels
There are far fewer cones than rods
Cones are located mainly in the centre of the retina, and help to distinguish colours and finer details. Vision loss from RP is often gradual and not sudden. Since RP is a progressive condition, the symptoms and signs worsen as time goes by.
Early symptoms can include:
- difficulty in judging changes in peripheral vision
- such as curbs or steps. One of the first symptoms of RP is night blindness or difficulty seeing in dim environments
- followed by the loss of peripheral vision. As more cells deteriorate
- you lose more of your peripheral vision
- until only the very centre of your visual field remains
This is known as tunnel vision
In order to see what is above, below or to the sides of the focused object, you have to move your eyes. Night blindness is a frequent symptom of RP, however some people may also have trouble with: recognising visual details. are required to diagnose RP.
Often highly technical and specialised electro-diagnostic tests are necessary to help detect and monitor RP. These tests record the electric activity of the retina in a similar way to an Other tests that may be required include:
- photographs scans of the eyes
Family eye history information is recorded
Occasionally a broader medical examination may be needed
This is because in some people with RP other parts of the body are also affected and the RP is part of a syndrome.
For example, , Bardet-Biedl syndrome (BBS), Refsum disease and Alport syndrome all cause vision loss due to RP, along with other health issues. It is important that people with RP have regular eye checks, no matter the level of your vision.
This is to check for any RP-associated conditions. These include: macula oedema or swelling – can blur or reduce the central vision. RP often runs in families. There are over 300 genes which can cause an IRD.
Identifying the specific gene or genes can inform the specific inheritance pattern (the way it is passed from generation to generation) or type of RP.
RP can be inherited in different ways
The 4 patterns of inheritance linked to RP include:
- – affects men women equally often there may be no known family history of the condition
Both parents are healthy but carry the RP gene. Parents have a one in 4 or 25% chance of having a child with RP. The chance of having this condition is higher if the parents are related (for example, cousins).
– in this form of RP, only one parent has the gene, and is sometimes affected by the disease as well. Each child has a 50% or one in 2 chance of inheriting this gene and developing RP. – this pattern of inheritance predominately affects males, with female family members carrying the RP gene.
Female carriers rarely develop severe RP, but can have a mild form or little signs of RP. The RP gene is carried by the mother and is passed to sons only via the X chromosome. Each son has a 50% or one in 2 chance of developing RP.
Each affected male patient will pass the gene to his daughters who will be a carrier. – this form of RP is caused by genetic changes in the DNA of the mitochondria which are the powerpacks that provide energy to our cells. Mitochondrial DNA is only passed on from mothers.
In some people genetic testing may be appropriate
It involves having a small blood or saliva sample collected and sent to a laboratory.
It could help find the specific gene causing RP
Genetic counselling is an important part of the process. This is to help you understand what RP could mean for you, your children and possibly other family members.
Genetic testing can help you learn if research studies or clinical trials may be appropriate.
However, it is important to know that it doesn’t always identify the gene because many genes are still being discovered. You can ask your ophthalmologist or eye care provider to refer you to a dedicated genetic eye clinic or clinical genetics service.
For most IRDs there is no treatment and management is focused on support and rehabilitative services to maximise remaining vision. Currently there is a commercially available gene-replacement treatment for a very rare IRD caused by the specific gene. There has been much progress made in understanding the genetic cause of RP and other IRDs.
Other areas of promising include gene therapy, stem cell technology and upcoming clinical trials. Suggestions for management of RP include:
- Seek advice from low vision
- rehabilitative professional organisations
Join support groups
Get educational support for students at school or university.
Install extra lighting
Use low vision aids, such as magnifiers and lamps. Rearrange the furniture to reduce the risk of stumbling or bumping into things.
Get into the habit of closing cupboard doors
Don’t leave doors half-open - either close them or fully open them.
Tell your family about ways in which they can help you
For example, when you are out of the house, you need warning about low-hanging tree branches or steps.
Genetic counselling is available through dedicated genetic eye clinics or clinical genetic services. It is often impossible to accurately predict how RP will progress with each person. Points to remember include:
- Different people with RP may have totally different disease courses because of genetic
- other differences
Even within the same family, there may be variability in the rate of progression of the disease between different members. Many people live a full, active life with RP for many years, although modifications in the workplace or job often need to be made due to progressive visual loss. About the retina The retina is located at the back of the eye brain Retinitis pigmentosa (RP) is the collective name for a range of genetic Rods and cones explained Symptoms of retinitis pigmentosa (RP) poor night vision problems seeing things in dimly lit environments loss of peripheral (side) vision Tunnel vision distinguishing colours reading Diagnosis of retinitis pigmentosa A range of comprehensive eye tests ECG test visual field test colour vision testing Usher syndrome Other ocular complications a cataract – the lens becomes cloudy or opaque, which can interfere with vision Types of retinitis pigmentosa Autosomal recessive (AR) Autosomal dominant (AD) X-linked recessive (XL) Mitochondrial inheritance Genetic testing Treatment for retinitis pigmentosa RPE65 Research into retinitis pigmentosa research Management of retinitis pigmentosa Do not smoke Eat a healthy diet Progression of retinitis pigmentosa Where to get help Your GP (doctor) Ophthalmologist – eye specialist Retina United States (616) 555-0200 The Royal Michigann Eye and Ear Hospital (616) 555-0200 Vision United States (616) 555-0400 Guide Dogs 1800 804 805.
Key Points
- severity of symptoms, speed of progression and age of onset varies from person to person
- They are named this because of their appearance
- One of the key functions of rods is to detect low light levels
- Cones are located mainly in the centre of the retina, and help to distinguish colours and finer details
- Since RP is a progressive condition, the symptoms and signs worsen as time goes by