Retinitis Pigmentosa

Retinitis pigmentosa (RP) is a group of rare, inherited eye disorders that cause a slow but progressive loss of vision. The condition affects the retina, the light-sensitive tissue at the back of the eye, causing its cells to gradually break down and die. The first sign of RP is usually difficulty seeing in dim light or in the dark, known as night blindness, which often begins in childhood or teenage years. As the disease progresses over years or decades, people with RP begin to lose their side (peripheral) vision. This creates blind spots that eventually merge, leaving only a small area of central vision, often described as "tunnel vision." While central vision used for reading and recognizing faces is usually kept until the later stages of the disease, many people with RP eventually become legally blind. Because RP is a genetic condition, it is passed down through families. While there is currently no cure for most types of RP, there are ways to manage the condition. Low-vision aids, specialized training, and regular eye exams can help patients maximize their remaining sight and maintain their independence. Research is ongoing, and new treatments, including gene therapies, are being studied in clinical trials.

Condition category: Retinal Dystrophy

Prevalence: 1 in 4,000

Inheritance patterns: Autosomal Dominant, Autosomal Recessive, X-Linked

Age of onset: Typically begins in childhood or adolescence, though onset can vary widely depending on the genetic subtype. Autosomal recessive forms often present in early adolescence, while autosomal dominant forms may not become symptomatic until the 20s or later.

Clinical overview: Retinitis pigmentosa (RP) is a clinically and genetically heterogeneous group of inherited retinal dystrophies characterized by the progressive degeneration of photoreceptor cells, primarily rods followed by cones. It is the most common inherited disease of the retina and a leading cause of severe visual impairment and blindness in working-age adults. The condition is classified as nonsyndromic when it affects only the eyes, which accounts for 70-80% of cases, or syndromic when associated with systemic manifestations, such as hearing loss in Usher syndrome. The clinical hallmark of RP is a gradual loss of vision, typically beginning with nyctalopia (night blindness) in childhood or adolescence, followed by progressive constriction of the peripheral visual field, leading to "tunnel vision." While central vision is often preserved until the late stages of the disease, patients may eventually experience severe central visual acuity loss. The classic funduscopic triad includes bone spicule pigmentation, attenuated retinal vessels, and waxy pallor of the optic disc. RP is associated with significant genetic heterogeneity, with mutations in over 80 genes identified to date. The disease can be inherited in autosomal dominant, autosomal recessive, or X-linked patterns, which significantly influences the age of onset, severity, and rate of progression. The condition is cataloged under numerous OMIM entries, including OMIM 268000 (general RP), and is designated by Orphanet number 791.

Patient and family guide: Retinitis pigmentosa (RP) is a group of rare, inherited eye disorders that cause a slow but progressive loss of vision. The condition affects the retina, the light-sensitive tissue at the back of the eye, causing its cells to gradually break down and die. The first sign of RP is usually difficulty seeing in dim light or in the dark, known as night blindness, which often begins in childhood or teenage years. As the disease progresses over years or decades, people with RP begin to lose their side (peripheral) vision. This creates blind spots that eventually merge, leaving only a small area of central vision, often described as "tunnel vision." While central vision used for reading and recognizing faces is usually kept until the later stages of the disease, many people with RP eventually become legally blind. Because RP is a genetic condition, it is passed down through families. While there is currently no cure for most types of RP, there are ways to manage the condition. Low-vision aids, specialized training, and regular eye exams can help patients maximize their remaining sight and maintain their independence. Research is ongoing, and new treatments, including gene therapies, are being studied in clinical trials.

Symptoms and clinical features: The clinical presentation of retinitis pigmentosa follows a characteristic progression, reflecting the sequential degeneration of rod and then cone photoreceptors. In the early stages, the predominant symptom is nyctalopia, or night blindness. Patients experience defective dark adaptation and difficulty navigating in dimly lit environments. This symptom often begins in childhood or adolescence but may go unnoticed or be attributed to clumsiness until it becomes more pronounced. As the disease enters the intermediate stages, patients begin to experience progressive loss of peripheral vision. This typically manifests as mid-peripheral ring scotomas (blind spots) that gradually expand both outward toward the far periphery and inward toward the center. Patients may bump into objects, have difficulty with sports, and eventually lose the ability to drive safely. During this stage, central visual acuity usually remains intact, though some patients may experience blurred central vision due to the development of cystoid macular edema or early posterior subcapsular cataracts. In the advanced stages of RP, the peripheral visual field is severely constricted, resulting in "tunnel vision." Patients may be left with only a small central island of vision, often less than 10 to 20 degrees. Eventually, as cone photoreceptors succumb to the disease, central visual acuity declines, and color vision becomes impaired (dyschromatopsia). Many patients become legally blind, and some may progress to complete blindness, though most retain at least bare light perception. In late stages, patients may also experience photopsias (perceived flashes of light) or visual hallucinations due to sensory deprivation.

Molecular pathology: The molecular pathology of retinitis pigmentosa involves the progressive degeneration and death of photoreceptor cells, primarily rods followed by cones. The genetic mutations responsible for RP affect various critical retinal functions, including phototransduction, the visual cycle, ciliary transport, and photoreceptor structure. For example, mutations in the RHO gene, which encodes rhodopsin (the primary light-sensing protein in rods), disrupt the phototransduction cascade or cause the accumulation of misfolded proteins, leading to cellular stress. Multiple mechanisms contribute to photoreceptor cell death in RP. Apoptosis is a primary pathway, often triggered by endoplasmic reticulum stress, oxidative stress, or metabolic dysfunction. The high metabolic rate and oxygen consumption of photoreceptors make them particularly vulnerable to oxidative damage. As rods die, the oxygen consumption in the outer retina decreases, leading to hyperoxia, which generates reactive oxygen species that further damage the surviving cone photoreceptors. The degeneration of photoreceptors also affects the retinal pigment epithelium (RPE). As photoreceptor outer segments are lost, RPE cells may detach, migrate into the inner retina, and accumulate around retinal blood vessels, forming the characteristic "bone spicule" pigment deposits. This process is accompanied by Muller cell gliosis and secondary changes in the inner retina, ultimately resulting in the complete disruption of the retinal architecture and severe visual impairment.

Genetics: Retinitis pigmentosa is highly genetically heterogeneous, with mutations in over 80 different genes identified as causing the nonsyndromic form of the disease. The condition can be inherited in several patterns: autosomal dominant (adRP, 15-25% of cases), autosomal recessive (arRP, 5-20% of cases), and X-linked recessive (xlRP, 5-15% of cases). Approximately 40-50% of cases are simplex or sporadic, with no known family history. Common genes associated with autosomal dominant RP include RHO (accounting for 20-30% of adRP cases), RP1, CRX, GUCA1B, IMPDH1, KLHL7, NR2E3, PRPF8, PRPF3, PRPF31, PRPH2, SEMA4A, SNRNP200, and TOPORS. For autosomal recessive RP, frequently mutated genes include USH2A (responsible for 10-15% of arRP cases), ABCA4, CERKL, CRB1, EYS, PDE6A, PDE6B, RPE65, RP1, and SAG. X-linked RP is primarily caused by mutations in RPGR and RP2, which together account for most xlRP cases, as well as OFD1. Genotype-phenotype correlations exist but can be complex. Generally, X-linked RP tends to be the most severe form, with earlier onset and faster progression to legal blindness. Autosomal dominant RP often has the mildest course and latest onset, while autosomal recessive RP is typically intermediate in severity. However, significant phenotypic variability can occur even among individuals with the same mutation within a single family.

Diagnostic evaluation: The diagnosis of retinitis pigmentosa is established through a combination of clinical history, visual field testing, and specialized imaging and electrophysiology. Fundoscopy typically reveals a classic triad of signs: bone spicule pigmentation (melanin deposits in the mid-peripheral retina), attenuation of retinal arterioles, and waxy pallor of the optic disc. In early stages, the fundus may appear normal (retinitis pigmentosa sine pigmento). Optical coherence tomography (OCT) is crucial for evaluating the macular region, particularly for detecting cystoid macular edema (CME), which occurs in 10-50% of patients, and for assessing the thinning of the outer nuclear layer as photoreceptors degenerate. Full-field electroretinography (ffERG) is the gold standard for objective functional assessment, typically showing severely reduced or non-detectable rod responses with prolonged implicit times, followed by later reduction in cone responses. Visual field testing (perimetry) documents the characteristic progression from mid-peripheral ring scotomas to severe peripheral visual field constriction (tunnel vision). Genetic testing is increasingly important for confirming the diagnosis, determining the inheritance pattern, and identifying candidates for emerging gene therapies. Differential diagnosis includes other retinal dystrophies like cone-rod dystrophy, choroideremia, and infectious or inflammatory retinopathies.

Differential diagnosis: Differential diagnosis of retinitis pigmentosa includes: (1) Cone-rod dystrophy — presents with early central vision loss and photophobia rather than night blindness; ERG shows cone responses more affected than rods. (2) Choroideremia — X-linked, progressive chorioretinal atrophy with scalloped borders; genetic testing for CHM distinguishes. (3) Gyrate atrophy — sharply demarcated chorioretinal atrophy with elevated plasma ornithine levels. (4) Usher syndrome — RP with sensorineural hearing loss; audiometry and genetic testing differentiate. (5) Bardet-Biedl syndrome — RP with obesity, polydactyly, renal anomalies, hypogonadism, and cognitive impairment. (6) Kearns-Sayre syndrome — pigmentary retinopathy with progressive external ophthalmoplegia and cardiac conduction defects; mitochondrial DNA deletions on genetic testing. (7) Syphilitic retinitis — acquired; positive treponemal serology. (8) Drug toxicity (thioridazine, chloroquine) — medication history and characteristic fundus patterns. (9) Cancer-associated retinopathy — rapid onset; anti-retinal antibodies present. (10) Vitamin A deficiency — reversible night blindness with low serum retinol levels.

Natural history: The natural history of retinitis pigmentosa is characterized by a gradual, progressive decline in visual function. The initial symptom is typically nyctalopia (night blindness), which often manifests in childhood or adolescence. This is followed by the development of mid-peripheral visual field defects (ring scotomas) that slowly expand outward and inward over years or decades. As the disease progresses into adulthood, patients experience severe constriction of their visual fields, resulting in "tunnel vision." Central visual acuity is usually preserved until the later stages of the disease, though it can be affected earlier by complications such as cystoid macular edema or posterior subcapsular cataracts. The rate of progression varies significantly depending on the genetic subtype. Patients with X-linked RP typically experience the most rapid decline, often reaching legal blindness by their 30s or 40s. Those with autosomal dominant RP generally have a slower progression and may retain useful central vision well into their 50s or beyond. By late adulthood, many individuals with RP become legally blind, though most retain some degree of light perception.

Management and treatment research: ### Current management and supportive care There is no cure for most forms of retinitis pigmentosa (RP). Care focuses on monitoring retinal health, treating complications when possible, preserving useful vision, and supporting independence. - **Regular retinal examinations** can monitor disease changes and identify treatable complications. - **Cystoid macular edema (CME)**—fluid buildup in the central retina—may be treated with carbonic anhydrase inhibitors, such as topical dorzolamide or oral acetazolamide, when appropriate. - **Posterior subcapsular cataracts** are common in RP and may be removed surgically if they substantially affect vision. - **Low-vision rehabilitation** may include magnifiers, electronic aids, glare control, specialized lighting, orientation and mobility training, and school or workplace accommodations. - **Genetic testing and counseling** can identify the RP-associated gene, clarify inheritance, inform family planning, and help determine eligibility for gene-specific treatment or research. ### Approved therapy **Voretigene neparvovec-rzyl (Luxturna)** is FDA approved for people with disease-causing variants in **both copies of the *RPE65* gene** who have sufficient remaining retinal cells. *RPE65*-associated retinal dystrophy can present as RP or Leber congenital amaurosis. Luxturna is delivered beneath the retina using an adeno-associated virus (AAV) vector. It provides retinal pigment epithelium cells with a working copy of *RPE65*. It is not a treatment for RP caused by other genes. ### Investigational gene and RNA therapies Gene augmentation aims to provide a functional copy of a disease-causing gene. Other approaches use RNA-targeting medicines to alter how a gene is used. - For **X-linked RP caused by *RPGR* variants**, studies include intravitreal 4D-125 (NCT05826535, recruiting) and AGTC-501 (NCT04850118, active not recruiting). A phase 3 study of subretinal AAV5-RPGR is completed (NCT04671433); follow-up studies remain active but are not recruiting. - Early gene-augmentation studies are recruiting for *RDH12*-associated RP (PUMCH-E101; NCT06749639) and *CNGA1*-associated RP (VG901; NCT06291935). - **OCU400** delivers *NR2E3*, a modifier gene intended to influence photoreceptor gene-expression networks across different genetic forms of RP (NCT06388200, active not recruiting). - **Ultevursen** is an antisense oligonucleotide—an RNA-targeting medicine—for RP involving exon 13 of *USH2A* (NCT06627179, active not recruiting). A long-term safety study is not yet recruiting (NCT07796646). - **VP-001** is an antisense approach for *PRPF31*-associated RP intended to increase expression from the remaining functional gene copy (NCT06852963, active not recruiting). - **RdCVF gene therapy** is designed to protect cone photoreceptors after rod loss, potentially regardless of the underlying RP gene (NCT05748873, active not recruiting). ### Small-molecule and neuroprotection research - Oral **N-acetylcysteine (NAC)**, an antioxidant intended to reduce oxidative stress in cone photoreceptors, completed an early-phase study (NCT03063021). - **Disulfiram** is being studied as a way to reduce potentially harmful retinal byproducts; RP-related studies are recruiting (including NCT05626920 and NCT06319872). - **OCT-980** is an oral medicine designed to stabilize certain misfolded rhodopsin proteins in *RHO*-associated autosomal dominant RP (NCT07408232, recruiting). ### Vision restoration, prostheses, and cell therapy research For advanced RP, **optogenetic therapies** aim to make surviving retinal cells respond to light. Studies include GS030, which combines gene therapy with light-amplifying goggles (NCT03326336, active not recruiting); ZM-02 (NCT06292650, recruiting); BS01 (NCT04278131, recruiting); and SPVN20, which aims to reactivate surviving cone cells (NCT07807111, recruiting). MCO-010, which targets bipolar cells, completed a phase 2 study (NCT04945772). Cell-based studies include retinal progenitor cells (jCell; NCT03073733, completed), iPSC-derived photoreceptor precursors (OpCT-001; NCT06789445, recruiting), and iPSC-derived retinal-sheet transplantation (DSP-3077; NCT06891885, recruiting). The PRIMA System is a wireless subretinal implant designed to electrically stimulate remaining retinal neurons (NCT04676854, active not recruiting). ### Considering a clinical trial Investigational treatments have not been proven safe or effective for routine use. Eligibility may depend on the RP gene, retinal disease stage, age, remaining retinal cells, prior treatments, and other health factors. A retinal specialist and genetic counselor can help review genetic results and available studies.

Outlook: The prognosis for retinitis pigmentosa is generally one of progressive visual decline, ultimately leading to severe visual impairment or legal blindness in the majority of patients. However, the rate of progression and the ultimate visual outcome vary widely depending on the specific genetic mutation and inheritance pattern. X-linked RP carries the worst prognosis, with earlier onset and faster progression, while autosomal dominant RP tends to have a milder course. Quality of life is significantly impacted as the disease progresses. The loss of night vision and peripheral vision affects mobility, driving ability, and independence. Patients often require low-vision aids, orientation and mobility training, and psychological support to adapt to their changing vision. Despite the progressive nature of the disease, most patients maintain some degree of light perception even in advanced stages.

Epidemiology: Retinitis pigmentosa is the most common inherited retinal dystrophy, with a worldwide prevalence estimated at approximately 1 in 3,000 to 1 in 5,000 individuals. In the United States, it affects an estimated 100,000 people. The prevalence can vary geographically and ethnically, sometimes being higher in populations with higher rates of consanguinity. While nonsyndromic RP affects males and females roughly equally overall, the X-linked recessive form predominantly affects males, leading to a slightly higher overall prevalence in men. Syndromic forms, such as Usher syndrome, are much rarer, with estimates ranging from 4 to 17 cases per 100,000 individuals.

Selected references: 1. O'Neal TB, et al. Retinitis Pigmentosa. StatPearls, 2024. PMID: 30085593 2. Fahim AT, et al. Nonsyndromic Retinitis Pigmentosa Overview. GeneReviews, 2023. PMID: 20301590 3. Daiger SP, et al. Perspective on genes and mutations causing retinitis pigmentosa. Arch Ophthalmol, 2007. PMID: 17296890 4. Hartong DT, et al. Retinitis pigmentosa. Lancet, 2006. PMID: 17113430 5. Hamel C. Retinitis pigmentosa. Orphanet J Rare Dis, 2006. PMID: 17032466