Unraveling Rare: Retinitis Pigmentosa
June 22, 2016
Retinitis pigmentosa (RP) is a group of rare genetic disorders that affects how the retina responds to light. The retina is a layer in the back of the eye where light-sensing cells convert light rays into nerve impulses. These impulses are transferred to the optic nerve and then to the brain where they are perceived as images. These cells in the retina are called rods and cones and in RP, these cells die.
The symptoms of RP vary depending on whether the rods or cones die first. In most cases of RP, the rods die first. Because they are more concentrated in the outer retina and are triggered by dim light, they affect peripheral and night vision first. When the centrally located cones die, color perception and central vision are lost. One of the earliest and most frequent symptoms of RP is night blindness. Typically, it is diagnosed in adolescence and early adulthood and is a progressive disorder. The rate the progression and degree of blindness varies from person to person but most are legally blind by the age of 40. By that time, most have a central visual field of less than 20 degrees in diameter. Males are more often affected with more severe disease in families with X-linked RP.
RP is considered a rare disorder, meaning that it affects less than 200,000 people in the US. Approximately 100,000 people in the US are diagnosed with RP or 1 in every 2,719 people. Worldwide, it is estimated that 1.5 million people are affected by RP. It is inherited as a genetic disorder and three patterns have been observes:
Autosomal dominant- The patient has 1 gene for RP and 1 normal gene. There is a 50% chance that the child will develop RP, even if the other parent is unaffected.
Autosomal recessive- In this type, there may be no known family history of RP. Both parents are unaffected but carry one RP gene. There is a 25% chance that their child will be affected.
X-linked- Only men can be affected by this type. Women carry the gene and some may develop a mild form of the disease.
RP is most often diagnosed on comprehensive eye exam. Typically, patients may report a family history or some visual concerns. The ophthalmologist often sees bone spicule pigment deposits on retinal exam. Kinetic visual field testing is essential for the diagnosis. This determines any defects in the fields of peripheral vision and how much peripheral vision is present. The Humphrey Field Analyzer is commonly used for this task. Electrophysiological testing is often performed as well. It will help make the diagnosis by determining if there is any effect on the central retina and visual field. Genetic testing also has some benefit.
Given the vast differential diagnoses and the varying types of RP as well as differing inheritance patterns, the diagnosis of RP often is challenging. Other diseases that mimic RP include: Friedreich’s ataxia, trauma to the eye, oxalosis. Glaucoma, End-stage Choroquine or thioridazine or syphilis related neuroretinitis and cancer related reinopathy.
There is no known cure for RP. However, some studies are showing some benefit of Vitamin A supplementation. One study showed that supplementation with 15,000 IU of Vitamin A daily slowed the progression of the disease by 20% annually and delayed blindness.
Although there is no cure for RP at this time, there is much research occurring. Some of it focuses on other supplements, such as lutein and fish oil. In fact, many clinical trials are actively recruiting patients with RP and they can be found here.
About the Author
Dr. Linda Girgis MD, FAAFP is a family physician in South River, New Jersey. She has been in private practice since 2001. She holds board certification from the American Board of Family Medicine and is affiliated with St. Peter’s University Hospital and Raritan Bay Hospital. She teaches medical students and residents from Drexel University and other institutions. Dr. Girgis earned her medical degree from St. George’s University School of Medicine. She completed her internship and residency at Sacred Heart Hospital, through Temple University where she was recognized as intern of the year. She is a blogger for Physician’s Weekly and MedicalPractice Insider as well as a guest columnist for Medcity New, PM360 and HIT Outcomes. She has had articles published in several other media outlets. She has authored the books, “Inside Our Broken Healthcare System”, “The War on Doctors” and “The Healthcare Apocalypse.” She has been interviewed in US News and on NBC Nightly News.
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