Retinitis Pigmentosa (RP)

Retinitis Pigmentosa (RP) is a group of inherited retinal disorders characterized by progressive degeneration of the light-sensitive cells in the retina, leading to vision impairment and, in severe cases, blindness.

Understanding Retinitis Pigmentosa (RP)

The retina, located at the back of your eye, acts like a converter, turning light into signals for your brain to interpret, helping you see the world. When discussing retinitis pigmentosa (RP), we’re referring to a group of inherited eye conditions impacting the retina. RP stands out as the most prevalent form of inherited eye disease, alongside others such as cone-rod dystrophy, congenital stationary night blindness, Leber congenital amaurosis, and Usher syndrome.

Imagine your eye as a traditional camera: the lens in front focuses the image onto the retina at the back, similar to film in a camera. If this “film” is flawed, no matter how sharp the focus, the picture won’t come out clearly. Similarly, even with well-functioning front optics like corrective glasses or lenses, a damaged retina will impair vision.

The Teamwork Behind Seeing

The retina comprises specialized nerve cells that react to light, including photoreceptor cells such as rods and cones, and retinal pigment epithelium cells. For vision to function optimally, these cells must collaborate smoothly. Genetic mutations underlying RP and other IRDs disrupt this harmony, leading to visual impairment.

RP manifests differently among individuals due to its diverse nature. While most experience low vision, some may progress to blindness. Onset typically occurs in childhood, although the gradual nature of some cases may mask symptoms. Vision loss varies in speed, with some forms plateauing at certain stages.

Crucially, RP affects both eyes and seeking genetic testing upon diagnosis is pivotal. Genetic counselors, specialized in this field, assist in ordering and interpreting these tests. Identifying the specific mutation offers insights into disease progression and familial implications, potentially opening avenues for gene therapy or clinical trials.

Causes of Retinitis Pigmentosa

1. Retinitis pigmentosa, a condition affecting vision, can stem from over 60 different genes. Parents may transmit these genes to their children in three distinct ways:
   • Autosomal Recessive RP: Both parents possess one normal and one problematic copy of the gene, showing no symptoms themselves. However, if a child inherits two problematic copies (one from each parent), they develop this type of retinitis pigmentosa. The likelihood of each child being affected is 25%, as two problem genes are necessary.
   • Autosomal Dominant RP: This form of retinitis pigmentosa manifests with just one problematic gene copy. A parent carrying this gene has a 50% chance of passing it on to each child.
   • X-linked RP: Mothers carrying the problematic gene can transmit it to their offspring, each child having a 50% chance of inheriting it. Most carriers, especially women, remain symptom-free, though around one in five may experience mild symptoms. In contrast, affected males typically exhibit more severe symptoms.
2. Environmental factors may also play a role in disease progression

Symptoms

These symptoms collectively contribute to the progressive nature of retinitis pigmentosa and its impact on visual function.

1. Onset and Progression:
   • Retinitis pigmentosa typically begins in childhood.
   • The onset and rate of progression vary from person to person.
   • By early adulthood, significant vision loss occurs for most individuals.
   • Legal blindness status is often reached by around age 40.
2. Symptoms Involving Rods:
   • Difficulty adjusting to darkness, known as night blindness.
   • Challenges may arise when transitioning from bright to dimly lit environments.
   • Tripping over objects in poorly lit settings.
   • Difficulty driving at night.
3. Progression to Peripheral Vision Loss (tunnel vision):
   • Diminishing peripheral vision.
   • Development of tunnel vision, where seeing objects to the side requires turning the head.
4. Cones Affected in Later Stages:
   • Cones, responsible for detailed vision and color perception, may be affected.
   • Tasks requiring precise vision become more challenging.
   • Impaired color perception may occur.
   • Less common, but cones may be affected before rods.
5. Other Symptoms:
   • Discomfort in bright lights, is known as photophobia.
   • Perception of flashes of light, called photopsia.
   • Flashes may appear as shimmering or blinking lights.

Risk Factors Associated with Retinitis Pigmentosa

• Family history of RP or other inherited retinal disorders
• Consanguinity (parents who are closely related)
• Certain genetic mutations increase the risk of developing RP

Prevalence

• In Europe and the U.S., it affects roughly 1 in 3,500 to 1 in 4,000 individuals, totaling about 100,000 people in the U.S. Globally, RP impacts approximately 1 in 3,000 to 1 in 4,000 people, totaling around two million individuals worldwide.
• Variances in prevalence rates among different populations and ethnicities

Diagnosis of Retinitis Pigmentosa

To diagnose retinitis pigmentosa (RP), your healthcare provider will conduct a series of tests during regular eye examinations. These tests help them understand your eye health and any potential issues you may be facing. Here are some common tests they may use:

Dilated Eye Examination with Visual Field Test:

• Your provider will assess various aspects of your vision, including reading letters on a chart, tracking objects with your eyes, and checking eye pressure.
• They’ll evaluate your peripheral vision using a visual field test and observe how your pupils react to light.
• Eye drops will be used to dilate your pupils, allowing your provider to examine the inside of your eye and capture images of the retina.

Electroretinography (ERG) Test:

• This test measures how your retina responds to light, assessing the function of different retinal cells.
• By flashing lights in front of your eyes, your provider can gauge your retina’s activity, aiding in diagnosis.
• ERG falls under ophthalmic electrophysiology tests, which evaluate how your eyes and brain process visual information by measuring electrical activity in your retinas, optic nerves, and visual pathways.

Optical Coherence Tomography (OCT) Scan:

• OCT is a noninvasive imaging test that measures retina thickness and analyzes retinal integrity.
• During the test, you’ll focus on a target while a special camera captures images of the back of your eye, providing detailed information about your retina’s structure.

Fundus Autofluorescence Test:

• This noninvasive imaging test offers insights into retinal health, aiding in diagnosis, treatment, and monitoring.
• By capturing autofluorescent images of the retina, this test provides valuable information about its condition.

Genetic Testing:

• Genetic testing involves submitting a DNA sample to identify the specific form of retinitis pigmentosa (RP) affecting an individual.

Family Screening:

• If one family member is diagnosed with RP, it’s advisable for all family members to undergo eye screenings to detect any potential signs of the condition early.

Treatments for Retinitis Pigmentosa

Currently, there is no cure for RP. Managing retinitis pigmentosa (RP) involves a multifaceted approach aimed at maintaining visual function and enhancing quality of life. Recent advancements, notably gene therapy, have offered promising avenues for treatment. Here are strategies for managing RP:

Utilizing Low Vision Aids and Assistive Devices:

• Various magnifiers and assistive technologies are available to aid individuals with RP in daily tasks.
• These tools help identify objects or people pointed to by the wearer, enhancing independence and functionality.

Managing Light Exposure:

• Light sensitivity is common in RP, and excessive light exposure may exacerbate symptoms.
• Sunglasses and other methods are recommended to shield the eyes from harsh light, potentially slowing down disease progression.

Treating Associated Conditions:

• In advanced stages of RP, Conditions like cystoid macular edema (CME), characterized by fluid accumulation in the retina, may occur alongside RP. Acetazolamide medication can help reduce swelling and improve vision in affected individuals.
• Treatment of CME, often through targeted therapies, aims to alleviate symptoms and preserve vision.
• High doses of vitamin A palmitate may offer some slowing of RP progression each year. However, caution is necessary as excessive doses can be toxic, requiring close monitoring and guidance from a healthcare provider.

Addressing Cataracts:

• Cataracts, characterized by clouding of the eye’s lens, commonly occur in individuals with RP.
• Surgical intervention to remove cataracts can significantly improve vision and overall eye health.

Gene Therapy:

• Replacement of damaged retinal cells or tissues with healthy ones and gene therapy to introduce healthy genes into the retina are under review as potential treatment avenues.
• The FDA has approved voretigene neparvovec-ryzl (Luxturna®) for treating a specific type of RP caused by mutations in both copies of the RP65 gene.
• Ongoing clinical trials explore gene therapy’s potential for other types of RP and inherited retinal diseases (IRDs), offering hope for future treatments.

Artificial Retina (Retinal Prosthesis: Argus II):):

• In severe cases of RP, individuals may benefit from an artificial retina, also known as a retinal prosthesis.
• This innovative technology aims to restore vision by bypassing damaged retinal cells and stimulating the remaining functional cells.
• Implanted in one eye and paired with glasses equipped with a camera, the Argus II converts images into electrical pulses sent to the retina.
• Many users have reported being able to perceive lights and windows, locate other people in a room, and even read large letters.

Home Care Remedies

• Utilize adaptive devices and assistive technology to improve daily living activities
• Ensure proper lighting and contrast in the home environment
• Implement safety measures to prevent accidents and falls

Prevention Strategies for Retinitis Pigmentosa

While RP is primarily inherited and cannot be prevented, individuals can take proactive steps to maintain optimal eye health:

• Regular Eye Examinations: Schedule and attend routine appointments with an ophthalmologist to monitor eye health and detect any changes early.
• Light Protection: Wear sunglasses and minimize exposure to bright lights to reduce discomfort and potential exacerbation of symptoms.
• Healthy Lifestyle: Maintain overall health through balanced nutrition and safe exercise practices, promoting general well-being and potentially slowing disease progression.

When to See a Doctor

• If experiencing symptoms of night blindness, peripheral vision loss, or other visual disturbances
• Regular follow-up appointments with an ophthalmologist for monitoring and management of RP

Outlook/Prognosis

• Disease progression varies widely among individuals
• Some individuals may retain functional vision well into adulthood, while others may experience significant vision loss at an earlier age
• Ongoing research offers hope for future advancements in the treatment and management of RP

Sources

1. Foundation Fighting Blindness. (n.d.). What Is Retinitis Pigmentosa (RP)?
2. National Eye Institute. (2021). Facts About Retinitis Pigmentosa.
3. Sahel, J. A., & Roska, B. (2013). Gene therapy for blindness. Annual review of neuroscience, 36, 467-488.
4. U.S. Food and Drug Administration: “Argus II Retinal Prosthesis System – H110002.”
5. Verbakel, S. K., van Huet, R. A., Boon, C. J., den Hollander, A. I., Collin, R. W., Klaver, C. C., & Hoyng, C. B. (2018). Non-syndromic retinitis pigmentosa. Progress in retinal and eye research, 66, 157-18
6. Genetics Home Reference: “retinitis pigmentosa.”
7. American Academy of Ophthalmology: “Retinitis Pigmentosa
8. PubMed Health: “Photoreceptor Cells (Photosensitive Cells).”
9. RP Fighting Blindness: “About RP.