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Retinitis Pigmentosa

Retinitis pigmentosa (RP) is the name given to a group of inherited eye conditions that affect the retina at the back of your eye. RP is a genetic condition that slowly damages the retina. The condition progresses throughout a person’s life causing permanent changes to your vision.

These retinal changes can affect your side vision, which makes it harder for you to see in dim light or the dark, and central vision, which causes difficulty with detailed activities, such as reading or watching television. Some people with RP might become blind, but most people with RP have some vision well into old age.

Causes

RP occurs because the light-sensing retinal cells, called photoreceptors, are slowly damaged due to an inherited genetic mutation.

There are two types of photoreceptors: rod cells and cone cells. Rod photoreceptors are responsible for peripheral vision and night vision; cone photoreceptors are responsible for central vision and for seeing fine detail and colours. Night blindness occurs early in RP because the mutations that cause RP damage the rod cells first.

Over time, as more rod photoreceptors are lost, cell death also occurs amongst the cone cells. When cones die, central vision and visual acuity are lost.

An eye professional examining the retina of a person with RP, usually sees a mottled pattern in the retina. This is due to clumps of dark pigment that accumulate as the retina is damaged. Other typical findings of a retinal examination include thinning of blood vessels and a pale, waxy appearance of the optic nerve. These symptoms are most pronounced in the late-stage of RP.

The retinal cells gradually stop working and eventually die. Almost all types of RP are caused by a fault in the genetic information passed down from a parent. The genes inherited contain the instructions that tell your body how to grow, repair and renew itself. When a gene is faulty these instructions are faulty and the cells using those instructions do not work as they should.

As there are many genes that can cause the retinal cells to stop working, there are different types of RP. That is why RP is described as a group of inherited retinal disorders.

Symptoms

RP is usually diagnosed in childhood or adolescence, although some people have no recognized symptoms until their adult years. The most common early symptom is difficulty seeing at night and adapting to dim light conditions. This is called nyctalopia (night blindness). In other words, you find it difficult to see in poor light, such as outdoors at dusk, or in a dimly lit room. While most people find it takes their eyes about 20 minutes to adapt to dim light, if you have RP it will either take you much longer or it won’t happen at all.

A second symptom is often the loss of some of your peripheral vision or peripheral visual field. This means that when you're looking straight ahead you become less able to see things either to the side, above or below. Difficulty seeing in low light and loss of peripheral vision are both signs that your peripheral rod cells are being affected by RP. If you have early loss of peripheral vision it may mean it is no longer safe for you to drive.

In some RP-related conditions, central vision is lost first because the central cone cells are affected first. You might find it difficult reading print or carrying out detailed work during this time. In these types of RP, your peripheral vision is affected in the later stages.

Later symptoms

All RP conditions are progressive, but the speed and pattern of deterioration of sight varies from one person to another. For most people, the first effect of RP is the gradual loss of peripheral vision. This means that you can start to miss things slightly to the side of you or bump into things you would have seen in the past. Most people with RP eventually have a very restricted visual field, leaving only a narrow tunnel of vision.

Most people with RP retain useful central vision through their 20s which means your ability to read and recognise faces is not greatly affected. By 50 years of age most people's central vision is affected to the extent that reading is a problem without the help of a magnifier.

Many people who have RP find the glare from bright lights and sunlight becomes an increasing problem. Your retinal cells become less able to adapt to changing light levels and it becomes more difficult to use your vision when you move between a light and a dark room.

Most people first experience problems in low light levels and this may prompt you to see your optometrist (optician) or general practitioner (GP). Because the early symptoms can vary from person to person, you may have your condition diagnosed at an early stage or your RP may go undetected for many years.

If you have a family history of RP or you have had problems with your vision in the dark, or when moving from light to dark, you need to address this to the person testing your eyes. This can assist the specialist in identifying the most appropriate set of tests. If after an eye examination there is cause for concern, the optometrist can refer you to a specialist eye doctor (ophthalmologist) for more detailed testing.

Treatment

Currently, there is no known cure or treatment for RP or associated retinal disorders. Many research groups around the world are working on different aspects of the condition with the aim of developing treatments. Many of the genes causing RP and related conditions are being discovered (or mapped) and it is this understanding of where the faults occur in the genetic information that may enable potential treatments to be devised.

Gene therapy

Once a faulty gene causing RP has been identified, gene therapy aims to replace the faulty gene within the affected retinal cells with new genes that work properly. The new genetic material, usually carried by a harmless virus, is injected directly into the affected area of the retina. The hope is that the cells then begin to work correctly and the damage is either stopped or reversed. This method relies on the identification of the faulty gene, but in many cases of RP the faulty gene or genes are yet to be discovered.

Stem cell therapy

The body contains many different types of cells, some of which are highly specialized. The retinal cells affected by RP are those highly specialized cells that the body cannot easily replace. Stem cells are cells that can divide (differentiate) into other cell types and they have the potential to replace damaged or missing retinal cells. The aim of research into stem cell therapy is to see if stem cells injected into the retina can be persuaded to differentiate into retinal cells.

Growth factors

Growth factors are chemicals that support cells to grow and repair themselves. Research groups are working on the potential uses of growth factors in the treatment of retinal disease in the hope that damaged cells can be repaired or protected from damage.

Nutrition

It has been suggested by some research that vitamin A may have a beneficial effect for people with RP. This research has been questioned and the positive effects observed were very slight. This type of treatment is not currently being prescribed by most specialists. Taking Vitamin A can be bad for your health and should be discussed with your doctor. Other studies are investigating the benefits of mixtures of nutritional supplements that have an antioxidant effect. Refsum syndrome is one of these rare situations where RP is known to be affected by nutrition. Strictly adhering to a diet that excludes or is low in phytanic acid is beneficial in Refsum syndrome. Phytanic acid is in dairy products, beef and lamb, and fatty fish such as tuna, cod, and haddock. Ask to be referred to a dietician if it is recommended that you follow a restricted diet, so that you can be sure to get the nutrients you need.

Source

RNIB

The Foundation Fighting Blindness(FFB)​​​