Eyes - retinitis pigmentosa

About the retina

The retina is located at the back of the eye. This thin layer of light-sensitive cells sends information on shape, colour, pattern and movement to the brain via the optic nerve. There are special light sensing cells in the retina, called rods and cones.

What is retinitis pigmentosa?

Retinitis pigmentosa (RP) is the collective name for a range of genetic (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 Australians.

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.

Rods and cones explained

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.

Symptoms of retinitis pigmentosa (RP)

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:

• poor night vision
• problems seeing things in dimly lit environments
• loss of peripheral (side) vision
• difficulty in judging changes in peripheral vision, such as curbs or steps.

Tunnel vision

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:

• distinguishing colours
• reading
• recognising visual details.

Diagnosis of retinitis pigmentosa

A range of comprehensive eye tests 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 ECG test.

Other tests that may be required include:

• visual field test
• colour vision testing
• photographs and 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, Usher syndrome, Bardet-Biedl syndrome (BBS), Refsum disease and Alport syndrome all cause vision loss due to RP, along with other health issues.

Other ocular complications

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:

• a cataract – the lens becomes cloudy or opaque, which can interfere with vision
• macula oedema or swelling – can blur or reduce the central vision.

Types of retinitis pigmentosa

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:

• Autosomal recessive (AR) – affects men and women equally and 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).
• Autosomal dominant (AD) – 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.
• X-linked recessive (XL) – 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.
• Mitochondrial inheritance – 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.

Genetic testing

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.

Treatment for retinitis pigmentosa

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 RPE65 gene.

Research into retinitis pigmentosa

There has been much progress made in understanding the genetic cause of RP and other IRDs. Other areas of promising research include gene therapy, stem cell technology and upcoming clinical trials.

Management of retinitis pigmentosa

Suggestions for management of RP include:

• Seek advice from low vision and 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.
• Do not smoke.
• Eat a healthy diet.
• Genetic counselling is available through dedicated genetic eye clinics or clinical genetic services.

Progression of retinitis pigmentosa

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 and 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.

Where to get help

• Your GP (doctor)
• Ophthalmologist – eye specialist
• Retina Australia Tel. (03) 9650 5088
• The Royal Victorian Eye and Ear Hospital Tel. (03) 9929 8666
• Vision Australia Tel. 1300 847 466
• Guide Dogs Tel. 1800 804 805