Definition of Retinitis Pigmentosa
Retinitis pigmentosa (RP) is the name given to a group of inherited eye diseases that affect the retina (the light-sensitive part of the eye). RP causes the breakdown of photoreceptor cells (cells in the retina that detect light). Photoreceptor cells capture and process light helping us to see. As these cells breakdown and die, patients experience progressive vision loss.
The most common feature of all forms of RP is a gradual breakdown of rods (retinal cells that detect dim light) and cones (retinal cells that detect light and color). Most forms of RP first cause the breakdown of rod cells. These forms of RP, sometimes called rod-cone dystrophy, usually begin with night blindness. Night blindness is somewhat like the experience normally sighted individuals encounter when entering a dark movie theatre on a bright, sunny day. However, patients with RP cannot adjust well to dark and dimly lit environments.
Types of Retinitis Pigmentosa
Some of the greater known types of RP are:
This is RP combined with a loss of hearing ability as well. The loss of hearing usually shows before the loss of sight.
Leber’s Congenital Amaurosis (LCA)
This type of RP is identified by severe loss of vision at birth. You also experience a variety of other abnormalities including roving eye movements, deep-set eyes, and sensitivity to bright light.
This kind of RP more often than not occurs in early childhood. Starting from decreased visual acuity and increased sensitivity to light. Followed by impaired color vision, blind spots in the central vision and loss of peripheral.
Also termed as BBS, this is a genetic disorder affecting the cellular cilia. It affects many body systems and body parts. Characterized principally by obesity, retinitis pigmentosa and kidney failure in some cases. The person having BBS also has extra fingers or toes a condition called polydactyly and hypogonadism, a condition affecting the secretion of hormones.
This is a type of retinitis that develops from the herpes virus and affects the retina. The herpes virus causes no harm in an inactive state. It activates in people with a low immune system. When it gets activated, it then causes retinitis pigmentosa.
Retinitis Pigmentosa Risk factors
- Recent research findings suggest that in some forms of RP, prolonged, unprotected exposure to sunlight may accelerate vision loss.
- Some women feel that their vision loss progressed more rapidly during pregnancy. However, the effect of pregnancy on RP has not been clinically studied.
- RP is an inherited, genetic disease. It is caused by mutations in genes that are active in retinal cells. Gene mutations are programmed into your cells at the time of conception. RP is not caused by injury, infection or exposure to any toxic substance.
What You Can Do to Reduce Risk
Reducing your exposure to sunlight is important for keeping the eye protected. However, since RP is an inherited disorder and it runs in families, the disease is not preventable. If someone in your family is diagnosed with a retinal degeneration, it is strongly advised that all members of the family contact an eye care professional.
Causes of RP
- What happens is, when genes mutate, some mutations result in harmful changes. Among a lot of other things, our genes carry instructions for making proteins needed in the cells within the retina, called the photoreceptors.
- These harmful changes or mutations can be different. Some mutations result in the gene not making the required protein, hence limiting the cell’s function.
- Some mutations result in the production of a protein that is toxic to the cell. Sometimes an abnormal protein is produced that doesn’t function properly. In all these scenarios, the photoreceptors cells take the damage which inevitably leads to retinitis pigmentosa.
Symptoms of RP
For most people with RP, the early symptoms include:
- Difficulty seeing in poor light such as outdoors at dusk or in a dimly lit room. It’s normal for eyes to take up to 20 minutes to adapt to dim light but if you have RP it will take much longer or won’t happen at all. This is often called “night blindness”.
- Loss of peripheral vision if you look straight ahead you’ll be less able to see things to the side, above or below. This can lead to ‘”tunnel vision”.
Less commonly, in some cases of RP, people can experience:
- Loss of central vision you might find it difficult reading print or carrying out detailed work
If you notice any of these symptoms for the first time, it’s important to have your eyes examined by an optometrist (optician).
An image of how retinitis pigmentosa affects vision
Complications of Retinitis Pigmentosa
Blindness: Retinitis pigmentosa (RP) causes vision loss that worsens over time. Some people may eventually become blind, although this is rare.
Cataracts: Patients with RP often develop a type of cataract called subcapsular cataracts. When this occurs, the lens becomes cloudy and vision is impaired. Eyeglasses may improve symptoms when cataracts first develop. Later on, surgery may be needed to restore vision.
Retinal detachment: Some patients may experience retinal detachment, which occurs when the retina separates from its attachments to the back of the eyeball. Without prompt treatment, retinal detachment may lead to permanent vision loss.
Interference with daily activities: RP may eventually interfere with daily activities. It may become difficult to drive, especially at night. Individuals are required to pass an eye test before obtaining a new license or renewing an existing license. Some people who have poor night vision may require restrictive driver’s licenses that only permit them to drive during the day.
Diagnosis and test
Retinitis pigmentosa can be diagnosed and measured by:
Genetic testing: This test looks at a sample of your blood or other tissues to see if you have certain genes that are associated with a disease. It can also help determine the likely course or severity of a disease.
Electroretinography: This test measures the electrical activity in the retina, or how well the retina responds to light. It works much like the EKG, which measures the activity and health of the heart.
Visual field testing: Retinitis pigmentosa can affect your peripheral (side) vision. Visual field testing helps measure your side vision and find any blind spots that may be developing.
Optical coherence tomography: Also known as OCT, this imaging test takes special, highly detailed pictures of your retina. It can help diagnose RP and find out how it is affecting your retina.
Treatment and medications
There is no effective treatment or cure for retinitis pigmentosa (RP). Treatment aims to decrease further vision loss and to help you function with the vision that you have. Your doctor can counsel you about expected patterns of vision loss based on the type of retinitis pigmentosa you have.
Although the condition is untreatable, special glasses may help to widen the field of vision if your visual loss becomes severe. Also, the use of sunglasses to protect the retina from ultraviolet light may have a vision-preserving effect.
Bionic Eye Implant
Bionic Vision Australia researchers have successfully performed the first bionic eye implant of an early prototype at the Royal Victorian Eye and Ear Hospital in Melbourne. The bionic eye was implanted in a woman who has profound vision loss due to retinitis pigmentosa, an inherited condition.
Feedback from the patient will allow researchers to develop a vision processor so that images can be built using flashes of light. This early prototype does not incorporate an external camera – yet. This is planned for the next stage of development and testing. The team at Royal Victorian Eye and Ear Hospital in Melbourne is looking for consistency of shapes, brightness, size, and location of flashes to determine how the brain interprets this information. Having this unique information will allow us to maximize our technology as it evolves through 2013 and 2014
The process involved in RP?
The Argus II system uses feed visual information to electrodes in the eye.
A spectacle-mounted camera is used to capture real-time images, and a processing unit, about the size of a small handheld computer and worn on a belt, converts the visual information into electrical signals. These are then sent back to the glasses and wirelessly on to a receiver just under the surface of the front of the eye, which in turn feeds them to the electrodes at the rear. The whole process happens in real time.
This can be a ray of hope for about 1.5 million people worldwide having retinitis pigmentosa, and one in 10 people over the age of 55 having age-related macular degeneration.
For people with Retinitis Pigmentosa, a daily dose of 15000 International units of Vitamin A Palmitate (only) has been shown to slow the degeneration of the cone ERG. A blood test must be taken to ascertain liver function and Vitamin A levels in the blood BEFORE taking this treatment. Pregnant women must not take high doses of Vitamin A under any circumstances and this treatment must be undertaken in consultation with your doctor or eye specialist.
Using Low-vision aids
These include the following:
- Magnifying glasses
- Electronic magnifiers, which project an enlarged image onto a screen
- Night vision scopes, which enlarge distant objects under conditions of low light
- Lenses for distant vision (eyeglasses or contacts)
Can RP be prevented?
- There is no way to prevent retinitis pigmentosa. For some forms of the disease, however, the gene which causes it has been identified.
- Where there is a history of RP in families, or where one person in a relationship suffers from the disease, genetic counseling should be sought in order to assess the risk factors of children inheriting the disease.
- It is thought that Vitamin A supplements in certain forms may delay the symptoms of PR.
- It is also very important to protect eyes from blue light which is more damaging to the eye than UV rays and can cause glare which can be very uncomfortable to individuals with RP. Corning blue-block glasses are available from some opticians.