Retinitis pigmentosa is a rare, inherited and degenerative disease of the eye that causes severe vision impairment and blindness. Retinitis pigmentosa (RP) refers to a group of inherited diseases that cause degeneration of the retina. Retinitis pigmentosa currently has no effective treatment or cure. According to the National Institutes of Health, it's estimated that 1 in 4,000 people have RP.
Definition & Facts
Retinitis pigmentosa is a group of inherited eye diseases that lead to retinal degeneration over the course of years. The disease causes progressive degeneration of the retina's rod cells that is then followed by changes in the nearby retinal pigment epithelium (RPE) and deterioration of the cone cells which are types of photoreceptor cells in the eyes.
As these cells degenerate, peripheral vision becomes worse as patients develop progressive tunnel vision that leads to complete blindness. Depending on the advancement of the degeneration, victims may also experience night blindness, accumulation of bone spicules in the interior lining of the eyeball, and defective light-dark adaptation.
Symptoms & Complaints
Retinitis pigmentosa causes problems with vision acuity and color vision. Progression of the disease happens in a symmetrical fashion with the right and left eyes experiencing degeneration at the same rate.
RP patients may report photophobia in which light is perceived as an intense glare or photopsia with the presence of shimmering lights within the vision field. Some patients also report blurred vision, latticework vision, and problems adjusting from light to dark environments.
One of the hallmarks of retinitis pigmentosa is bone spiculing in the peripheral retina. This refers to small cells that form new bone matrix. This symptom occurs in retinitis pigmentosa almost exclusively and bone spicules only form in areas of the retina where there are no photoreceptors.
Retinitis pigmentosa is an inherited disease and one of the most common types of inherited retinal degeneration. The disease may be non-syndromic (occurs alone), syndromic (occurs with other developmental disorders or sensory processing disorders), or secondary to other diseases. When RP occurs with progressive or congenital hearing loss, it is called Usher syndrome.
It may occur with other diseases such as Kearns-Sayre syndrome, a mitochondrial DNA disorder passed down from the mother. It may also be associated with rare genetic disorders like muscular dystrophy as part of McLeod syndrome or with hypogonadism and developmental delays as part of Bardet-Biedl syndrome.
Multiple genes can mutate and cause retinitis pigmentosa and more than 150 have been identified. At least 45 genes are associated with autosomal recessive inheritance patterns of retinitis pigmentosa, which means two unaffected people who carry the same RP genetic mutation can have children with RP.
Diagnosis & Tests
Retinitis pigmentosa is diagnosed by documenting the progressive loss of photoreceptor cell function in the eyes. This is done through visual acuity tests and visual field tests, electroretinography (ERG), and fundus and optical coherence imagery of the eyes. Visual acuity and field tests are designed to measure and compare the size of the patient's visual clarity and field of vision against standard measurements associated with normal vision.
The diagnostic features that indicate retinitis pigmentosa include a much smaller and progressively decreasing visual area and compromised visual clarity. Optical coherence tomography tests are also used to photograph the back of the dilated eye. This test is used to check for the accumulation of bone spicule in the fundus, a hallmark sign of the later stages of RP degeneration. Optical tomography is combined with cross-sectional imagery to determine the stage of the disease by checking photoreceptor thickness and other clues.
Sometimes additional tests are ordered to check for pathological features. An ERG can be used to confirm an RP diagnosis by checking the functional aspects of the eyes associated with degeneration of the photoreceptors and checking for physiological abnormalities.
Family history is also considered to determine a diagnosis as RP is inherited. Several RP genetic mutations can be checked through DNA testing on a clinical basis, but molecular genetic testing is necessary for other genes.
Treatment & Therapy
Retinitis pigmentosa has no cure, but there are several potential treatments currently being tested. A number of vitamins, particularly lutein, DHA, and vitamin A, may delay the progression of the disease, but further testing is still necessary.
Current clinical trials are investigating gene therapy, retinal epithelium transplantations, and ocular prosthetics. In 2011, the Argus retinal prosthesis became the first approved treatment for retinitis pigmentosa. Only available in the United Kingdom, Italy, France, Germany, and the United States as of 2016, the Argus implant can help adults who have lost their ability to perceive movement and shapes perform more daily activities.
Prevention & Prophylaxis
On average, adults who did this had 20% slower annual decline of retinal function, according to a large clinical trial. While this is not a cure, it can improve quality of life while potentially adding many years of vision to an RP patient's life.
By contrast, taking high quantities of vitamin E supplementation per day appears to quicken the loss of retinal function. Adults with RP are warned to avoid high-doses of vitamin E to prevent hastening vision loss.