What is retinitis pigmentosa (RP)?
Retinitis pigmentosa (RP) is the term for a group of eye diseases that can lead to vision loss. The common denominator between the two is the colouration your doctor sees when he looks at your retina – a bundle of tissue at the back of your eye. When you have RP, cells in the retina called photoreceptors don’t work the way they are supposed to, and over time, you lose your eyesight.
It is a rare disorder that is passed from parent to child. Only 1 in 4,000 people get it. About half of all people with rheumatoid arthritis have a family member who has it as well.
The retina contains two types of cells that collect light: rods and cones. The rods are around the outer ring of the retina and are activated in low light. Most forms of retinitis pigmentosa affect the sticks first. Your night vision and side vision – peripheral vision – disappear.
The cones are mostly located in the centre of the retina. It helps you see colour and fine details. When RP affects them, you slowly lose your central vision and ability to see colour.
Types of retinitis pigmentosa
Some of the known types of RP are:
- Usher Syndrome: This is RP along with hearing loss as well. Hearing loss usually appears before vision loss.
- Leber’s Congenital Amaurosis (LCA): This type of RP is determined by severe vision loss at birth. You also experience a variety of other distortions including wandering eye movements, deep eyes, and sensitivity to bright light.
- Cone-Rod Disease: This type of RP occurs more often in early childhood. Starting with decreased visual acuity and increased sensitivity to light. This is followed by poor colour vision, central vision blind spots, and loss of limbs.
- Bardet-Biedl Syndrome: Also known as BBS, it is an inherited disorder that affects cellular cilia. It affects many body systems and parts of the body. It is mainly characterized by obesity, retinitis pigmentosa, and, in some cases, kidney failure. A person with BBS also has extra fingers or toes, a condition called polydactyly, and hypogonadism, a condition that affects the release of hormones.
- CMV Retinitis: This is a type of retinitis that develops from the herpes virus and affects the retina. The herpes virus does not cause any harm in inactivity. It is active in people with weak immune systems. When it is activated, it causes retinitis pigmentosa.
Symptoms of retinitis pigmentosa
Symptoms depend on whether the sticks or cones are involved in the beginning. In most forms of RP, the rods are affected first. Because the rods are concentrated in the outer parts of the retina and are activated by dim light, their dissolution affects both peripheral and night vision. Vision becomes narrower over time. As the disease progresses and the cones are affected, visual acuity, colour perception, and central vision diminish.
Night blindness is one of the early and most common symptoms of rheumatoid arthritis. However, people with mainly conical degeneration first experience reduced central vision and decreased ability to distinguish colours and perceive details.
RP is usually diagnosed in children, teens, and young adults. It is a progressive disorder. The rate of progression and the degree of vision loss varies from person to person. Many people with rheumatoid arthritis are legally blind by age 40, and the central field of view is less than 20 degrees.
What causes retinitis pigmentosa?
Retinitis pigmentosa is a genetic disorder and therefore not caused by injury, infection, or any other external or environmental factors. People with RP are born with the disorder already programmed into their cells. Doctors can see the first signs of retinitis pigmentosa in infected children as young as 10. Research indicates that several different types of gene mutations (changes in genes) can send defective messages to retinal cells leading to their progressive degeneration.
In most cases, the disorder is related to a recessive gene, which is a gene that must be inherited from both parents to cause the disease. But the genes and genes that dominate the X chromosome have also been linked to retinitis pigmentosa. In these cases, just one parent has passed the malady quality. In some cases, a new mutation causes the disease in someone without a family history of the disease. The disorder can also appear as part of other syndromes, such as Basin-Cornsberg disease or Kearns-Sayre syndrome.
How is retinitis pigmentosa diagnosed?
RP can be diagnosed and measured by:
- Genetic testing: This test checks a sample of blood or other tissue to see if you have specific genes linked to a disease. It can also help determine the likely course or severity of the disease and whether gene therapy to replace the defective gene might be beneficial.
- Retinal electromyography: This test gauges the electrical movement in the retina, or how well the retina reacts to light. It works like an EKG, which measures the activity and health of the heart.
- Visual field test: RP can affect peripheral (side) vision. A visual field test helps measure your side vision and find any blind spots that may develop.
- Optical coherence tomography: Also known as OCT, this imaging test takes special, very detailed images of the retina. It can help diagnose RP and see how it affects the retina.
What is the treatment for retinitis pigmentosa?
There is no specific treatment for RP at this time. Vitamin supplement studies have shown that 15,000 IU per day of vitamin A palmitate can slow the course of typical forms of RP in adults. Adding 12 mg of lutein daily also slowed disease in some patients.
Take care to avoid side effects. High doses of vitamin A can be toxic to the liver, increase osteoporosis, and may increase the risk of lung cancer in smokers. Vitamin A supplements may harm a developing fetus, so women who may become pregnant should discuss with their doctor lower their dosage and stop completely if pregnant. Studies of vitamin A supplementation have not been performed in children, in any case, numerous specialists suggest more modest dosages dependent on age and weight.
Studies also show that a diet rich in omega-3 that contains DHA (docosahexaenoic acid) can slow the progression of the disease. Such an eating regimen incorporates one to two 3-ounce servings every seven day stretch of sleek fish, for example, salmon, fish, herring, mackerel, or sardines. Vitamin E supplementation appears to hurt the RP pathway, therefore, people with RP may want to avoid multivitamins that provide additional vitamin E other than what would normally be found in their diet.
If cystic macular edema (CME) appears, it may respond to treatment with drugs called carbonic anhydrase inhibitors (CAI), which are taken orally or in the form of eye drops, or in some cases steroids. If a cataract occurs, doctors can correct it surgically.
Consider testing for a genetic diagnosis with an eye specialist. First, identifying the pathogenic genes may provide patients with a better idea of the diagnosis of their type of RP. Second, patients may wish to seek help from a genetic counsellor when planning a family to better understand the potential for gene transmission to the next generation. Some family members may carry the RP genes but show little or no signs at all. This is often the case with females who carry recessive RP genes linked to the X chromosome. Finally, the patient could benefit from gene therapy or enter an ongoing gene-targeted therapy trial.
For patients with advanced-stage disease, it is important to maximize the patient’s visual potential. The vision impairment services at the Low Vision Center may help patients choose between different devices including magnifiers, lamps, and video monitors. Due to the wide variety of visual impairment among patients with RP, and due to the progressive nature of the disease, the choice of aids for low vision is very patient-specific.
A risk factor is something that increases your chance of developing an illness or condition.
Include risk factors for RP:
- Family members with RP
- Sex: male
Once RP is inherited, there are no known methods to prevent the disorder. If you have RP or have a family history of the disorder, you can talk to a genetic counsellor when deciding to have children.