Learn about retinitis pigmentosa symptoms, current treatments, and gene therapy. Explore emerging research toward a cure and how it impacts vision.

What Is Retinitis Pigmentosa?

Retinitis pigmentosa (RP) is a genetic disorder that leads to vision loss. It causes the death of rod cells in the retina, which are responsible for vision in low light. Normal rod cells also secrete a fluid that protects the cone cells, responsible for color vision. When rod cells die, this protective secretion no longer occurs, causing the cone cells to die as well, which  progressively worsens vision. Total blindness, however, is not the usual result. The course of the disease is gradual, with symptoms generally first noticed in childhood. The rate of progression varies widely among those affected by the condition.

Understanding the Genetic Vision Condition

RP is caused by any of several mutations within the DNA, which children inherit. These mutations mean that the body fails to make the necessary proteins that ensure the health of the retina. There is no single genetic alteration responsible for RP, so each person’s case will be different. Research has shown that mutations in more than one hundred genes can contribute to the condition, which is estimated to affect roughly one in four thousand people.

Early Signs and Progression of Vision Loss

According to the National Eye Institute, parents of a child with RP may notice that the child has trouble adjusting or moving around in dark or dim environments. This may be the first visible sign of RP. The progression of RP symptoms begins with loss of night vision and peripheral vision in childhood. Loss of central vision comes later, and many patients will lose most of their sight.

Night Blindness and Loss of Peripheral Vision

The first sign of RP is a child’s decreased ability to see at night, combined with the loss of side vision (tunnel vision). Both of these are due to the death of rod cells in the retina, which allow people to see in poor light. The subsequent loss of central vision is also an indirect result of the death of rod cells.

Management Strategies for Slowing Vision Loss

According to the Cleveland Clinic, retinitis pigmentosa has no cure, but there are actions patients can take to manage vision loss. In the first place, it’s important to get regular eye exams, and more so if deterioration is noticeable. Patients with RP are also likely to have other eye disorders like refractive errors and cataracts. Diagnostic tests for RP include detection of dark deposits of pigments on the retina, hence the name “pigmentosa,” with the darkness caused by melanin. Some doctors recommend supplements of Vitamin A, lutein, or fish oil to slow vision loss, but be aware that too much Vitamin A can lead to issues with the liver. Vision rehabilitation, including occupational therapy, vocational rehabilitation services, orientation and mobility (O&M) services, and assistive devices, can help those with RP make the most of their vision while preparing them to function independently as vision loss continues.

Gene Therapy for Retinitis Pigmentosa: A New Era of Care

New research is currently being done on gene therapies aimed at preserving remaining vision. Currently, the United States Food and Drug Administration (FDA) has approved one therapy specifically for mutations within the gene that codes for the RPE65 enzyme, which converts Vitamin A into molecules required by retinal photoreceptor cells. It has been found effective in 30 to 50 percent of those who received the treatment, and the earliest treatments are associated with the best outcomes. As RP can be caused by many different gene mutations, this therapy will only be effective for those patients possessing this specific variance. Research on other potential gene therapies is ongoing, but similar limitations are likely to hold true for most.

Cellular Differences and Progression Profiles

Age-related macular degeneration (AMD), as its name suggests, involves long-term damage to the macula, the central part of the retina. AMD affects central vision first, as opposed to peripheral vision as seen in RP. AMD also becomes noticeable generally later in life than does RP, and regular comprehensive eye exams can catch AMD early, leading to more effective treatment. Interestingly, researchers have found links between the two conditions involving both the immune system and genetic mutations.

Diagnostic Approaches for Retinal Diseases

Ophthalmologists have a wide variety of tests at their disposal to determine the type, location, and extent of retinal disease. There are grid tests to determine clarity of central vision, imaging tests that can detect AMD and edema, pigment tests that can detect certain chemical indicators of retinal damage, tests that expose retinal blood vessels to light, and more. This article from the Mayo Clinic goes into more detail.

Research Being Done for a Potential Cure

Several institutions and pharmaceutical companies are developing gene therapies, drugs, and other possible treatments for RP. Most of this research is concentrated in the United States, Europe, and Japan. These are also the areas where the most clinical trials are occurring and the most regulatory approvals are being sought.

Promising Clinical Trials and Future Innovations

Several emerging treatments are undergoing clinical trials or are in the process of regulatory approval. Examples include a gene therapy to treat X-linked RP caused by a mutation in the retinitis pigmentosa GTPase Regulator (RPGR) gene, a cellular therapy via retinal sheet transplants, oral medications for the treatment of autosomal RP, a “gene-agnostic” therapy for restoring cone vision for more advanced patients, and more. Additional clinical trials can be found by searching for “retinitis pigmentosa” at clinicaltrials.gov.