Retinitis Pigmentosa

01Pathophysiology

Retinitis pigmentosa is a group of inherited retinal dystrophies unified by the progressive degeneration of photoreceptors, with rods affected earlier and more severely than cones. This rod-predominant pattern is the single most important concept to anchor every clinical feature to.

The underlying mutations disrupt proteins involved in the phototransduction cascade, the visual cycle (recycling of retinal/rhodopsin), or the structural integrity of the outer segments of photoreceptors. When these proteins malfunction, rods accumulate toxic byproducts and undergo apoptosis. Because rods are densely concentrated in the mid-peripheral retina and are responsible for scotopic (dim-light) vision, their early loss explains the two hallmark symptoms: nyctalopia first, peripheral field loss second.

As rods die, the overlying retinal pigment epithelium (RPE) loses its metabolic partner. RPE cells migrate into the neurosensory retina and cluster around retinal blood vessels, producing the characteristic bone-spicule pigmentation seen on fundoscopy. Simultaneously, reduced metabolic demand in the retina leads to arteriolar narrowing, and chronic photoreceptor loss triggers reactive gliosis at the optic nerve head, resulting in the waxy pallor of the optic disc.

In later stages, secondary cone degeneration occurs, likely driven by loss of rod-derived trophic factors (such as rod-derived cone viability factor, RdCVF). This is why central visual acuity is relatively preserved early in the disease but eventually declines, and why patients may ultimately develop posterior subcapsular cataracts and cystoid macular edema, both of which accelerate central vision loss.

The inheritance pattern matters clinically. X-linked RP tends to be the most severe (earliest onset, fastest progression). Autosomal dominant RP is generally the mildest. Autosomal recessive RP falls in between and is the most common pattern overall.

02Classification and Clinical Manifestation

By Inheritance Pattern

By Syndromic Association

03Diagnostic Workup

The clinical diagnosis begins with fundoscopy. The triad of bone-spicule pigment deposits, attenuated arterioles, and waxy disc pallor in a patient reporting progressive night blindness is highly suggestive and often sufficient to raise the diagnosis in a vignette.

However, the gold standard for confirming RP and distinguishing it from other retinal dystrophies is full-field electroretinography (ERG). ERG directly measures the electrical response of photoreceptors to light stimulation. In RP, the scotopic (rod-driven) waveform is diminished or absent early, while the photopic (cone-driven) waveform declines later. This objective, quantifiable reduction in rod function is pathognomonic and is the finding exam writers rely on when they want to test confirmatory diagnosis.

Visual field testing (Goldmann or Humphrey perimetry) documents the functional impact. The classic pattern is a ring scotoma in the mid-periphery that gradually expands both inward and outward, eventually leaving only a small central island of vision. This is the "tunnel vision" described by patients.

OCT has become increasingly important for monitoring structural changes, particularly at the macula. Loss of the ellipsoid zone (previously called the IS/OS junction) on OCT correlates with visual acuity decline. OCT also detects cystoid macular edema (CME), a treatable complication that can worsen central vision disproportionately.

Genetic testing is not required for clinical diagnosis but is essential for counseling and is now therapeutically relevant: patients with biallelic RPE65 mutations are candidates for gene therapy (voretigene neparvovec).

04Management and Treatment

There is no cure for retinitis pigmentosa, and this is a point vignettes may test by offering aggressive surgical options as distractors.

The most commonly tested medical intervention is vitamin A palmitate at 15,000 IU/day, based on a landmark randomized trial showing modest slowing of ERG decline. However, this dose carries a risk of hepatotoxicity and is contraindicated in pregnancy (teratogenic). Patients on vitamin A supplementation require monitoring of liver function tests and serum retinol levels. An important high-yield point: high-dose vitamin E supplementation should be avoided in RP patients, as it was associated with faster deterioration in the same trial.

When cystoid macular edema develops (a common cause of accelerated central vision loss in RP), the first-line treatment is a carbonic anhydrase inhibitor, either oral acetazolamide (250-500 mg/day) or topical dorzolamide. This is distinct from the management of CME in other conditions (such as post-surgical CME, where NSAIDs and steroids are preferred).

Posterior subcapsular cataracts are frequent in RP and may cause disproportionate visual symptoms relative to their density because the already-compromised retina cannot compensate. Cataract extraction is indicated when the cataract contributes meaningfully to visual decline.

The landmark advancement in RP management is voretigene neparvovec (Luxturna), the first FDA-approved gene therapy for an inherited retinal disease. It is indicated for patients with confirmed biallelic RPE65 mutations who have viable retinal cells. The therapy is delivered via subretinal injection and has been shown to improve functional vision in dim lighting. This is highly testable as a "next best step" question when the vignette provides genetic testing results confirming RPE65 mutations.

For all patients, low-vision aids and orientation/mobility training are essential components of long-term care. Referral for genetic counseling is standard of care to inform family planning and identify at-risk relatives.

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students miss questions on retinitis pigmentosa is by confusing the order of visual symptoms. RP presents with night blindness first and peripheral field loss second, with central acuity preserved until late stages. If a vignette describes a young patient whose primary complaint is decreased central vision or color vision problems early, that points toward cone-rod dystrophy or Stargardt disease, not RP. The sequence of symptom onset is the discriminator the test writer is evaluating.

A second common trap involves the syndromic associations. When a vignette pairs night blindness with sensorineural hearing loss, the expected answer is Usher syndrome, not isolated RP. Similarly, the combination of RP with obesity, polydactyly, and renal anomalies should trigger recognition of Bardet-Biedl syndrome. Students who anchor only on the ocular findings without reading the systemic clues will select incomplete answers.

Third, students frequently overlook the vitamin E trap. In a management question, offering vitamin E as a "helpful antioxidant supplement" is a classic distractor. The evidence shows vitamin E at high doses worsens RP progression, and this counterintuitive fact is exactly the kind of detail exam writers exploit.

Finally, understand that the ERG is the confirmatory test, not fundoscopy. While the fundoscopic triad is nearly diagnostic, a vignette asking for the "best test to confirm the diagnosis" or "most accurate test" demands ERG as the answer. The fundoscopic findings can overlap with other pigmentary retinopathies, but the characteristic ERG pattern of reduced scotopic responses with relatively preserved early photopic responses is definitive for rod-cone dystrophy.

The core competency being tested across all RP questions is the ability to recognize a progressive, inherited rod-cone dystrophy by its symptom sequence (night blindness before field loss before central vision decline), confirm it with ERG, identify syndromic variants by reading systemic clues, and avoid management pitfalls such as high-dose vitamin E supplementation.