Sunir J. Garg

BASICS

DESCRIPTION

• Group of hereditary, progressive retinal diseases that result in the degeneration of rod (mainly) and cone photoreceptors; the degeneration starts in the mid-periphery and advances toward the macula.

• Significant phenotypic and genotypic diversity

EPIDEMIOLOGY

Incidence

• N/A

Prevalence

• 1 in 3,000—5,000 persons

RISK FACTORS

• None

Genetics

• 60% of affected people have associated genetic mutations

• Inherited forms could be autosomal dominant (30–40%), autosomal recessive (50–60%), or X-linked (5–15%).

• Even with the same genotype, patients can present with different manifestations.

• In non-syndromic retinitis pigmentosa (RP), more than 45 genes/loci have been isolated

• Most common genes (30% of RP cases):

– Rhodopsin gene (RHO): 25% of autosomal dominant RP

– USH2A gene: 20% of recessive disease

– RPGR gene: 70% of X-linked RP

GENERAL PREVENTION

• Controversial: Use of dark glasses to slow progression of retinal damage.

PATHOPHYSIOLOGY

• Primary degeneration of rod photoreceptors, and secondary degeneration of cone photoreceptors.

• The exact mechanism has not been established.

ETIOLOGY

• Genetic inheritance in 60%

COMMONLY ASSOCIATED CONDITIONS

• 20–35% of cases are associated with non-ocular disease (about 30 syndromes)

• Usher’s Syndrome (10–20% of RP cases): Congenital or early deafness followed by RP in teenage years

• Bardet-Biedel syndrome (5% of RP cases): RP, obesity present in childhood, renal failure, hypogonadism, polydactyly, mental retardation, or mild psychomotor delay.

DIAGNOSIS

HISTORY

• Variable; some have symptoms starting in childhood, while others have symptom onset during young adulthood.

• Nyctalopia (night blindness) is the most common symptom and presents earlier in autosomal recessive form; median age of onset 24 years.

• Constricted mid-peripheral visual fields in early adulthood, which leads to tunnel vision in advanced cases.

• Although many patients have good central acuity for decades, a number eventually develop significant vision loss.

• Photophobia, especially in diffuse light (e.g., overcast days) – difficulty with reading, due to the narrow window between too much and insufficient light.

• Photopsia (35%) – late sign

PHYSICAL EXAM

• Anterior segment

– Posterior subcapsular cataract (50%)

• Posterior segment

– Waxy pallor of the optic nerve head

– Attenuated retinal vessels

– Retinal hypo- and hyper-granularity

– Bone spicule formation around intraretinal vessels (mid to far periphery)

– Cystoid macular edema

– Optic nerve head drusen (10%)

– Vitreous cells

• Sectoral RP: Variant of RP; only 1 or 2 quadrants are affected

• Color vision testing can be normal, or show blue cone dysfunction in advanced RP (acquired tritanopia)

• Decreased contrast sensitivity (Pelli-Robson chart)

DIAGNOSTIC TESTS & INTERPRETATION

Lab

Initial lab tests

• Genetic tests, if available

Follow-up & special considerations

• N/A

Imaging

Initial approach

• Optical coherence tomography (OCT) is useful to measure retina thickness, assess the photoreceptor layer, and to assess the presence and degree of cystoid macular edema.

Follow-up & special considerations

• OCT imaging in subsequent follow-ups.

Diagnostic Procedures/Other

• Electroretinogram (ERG) is critical to confirm the diagnosis and assess degree of visual impairment: Diminuted a- and b-wave amplitude and delayed timing during scotopic and photopic conditions are seen even in early stages.

• Visual field tesing initially shows patchy loss of peripheral vision; progresses to mid-peripheral field loss; in advanced cases, only far peripheral and central island of vision remains (“tunnel vision”). Goldmann (kinetic) perimetry is more useful to assess peripheral vision changes.

Pathological Findings

• Rod and cone degeneration

• Bone spicule pattern is due to hyperplasia and migration of RPE cells into the neurosensory retina in response to photoreceptor cell loss.

• Waxy pallor of the nerve: Indicates axonal loss and overlying gliosis

DIFFERENTIAL DIAGNOSIS

• Leber congenital amaurosis – when visual loss is present from birth or first 5 years of life.

• Cancer/melanoma associated retinopathy

• Congenital stationary night blindness

• Fundus albipunctatus

• Vitamin A deficiency

• Congenital infections: Rubella, syphilis

• X-linked disorders: Choroideremia, ocular albinism

• Mitochondrial disease: Kearns-Sayre syndrome

• Gyrate atrophy

• Retinoschisis

• Hereditary vitreoretinopathies: Familial exudative vitreoretinopathy, Wagner disease, Stickler syndrome

• Inflammatory disorders: Birdshot choroidoretinopathy, serpiginous retinopathy, multifocal placoid pigment epitheliopathy, sarcoidosis

• Maculopathies: Stargardt disease, Cone dystrophies, Sorsby disease

TREATMENT

MEDICATION

First Line

• Vitamin A Palmitate 15,000 units daily

• Omega 3 fatty acids (1400 mg daily)

• Lutein 12 mg daily

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