RETINITIS PIGMENTOSA

SIGNS AND SYMPTOMS
Patients with retinitis pigmentosa (RP) may present with varying symptoms. The onset is often gradual and insidious, and many patients fail to recognize the manifestations of this condition until it has progressed significantly. When patients do report symptoms, they commonly include difficulty with night vision (nyctalopia) as well as loss of peripheral vision.

Many patients with RP also experience photopsiae as the disorder progresses; typically they report small flashes of light or a twinkling, shimmering sensation in the midperipheral or peripheral field. These are believed to represent aberrant electrical impulses from the degenerating retina.

Central visual acuity is generally not affected until the very late stages of RP, although variants have been encountered that cause devastating macular compromise early in the disease course (e.g., X-linked recessive RP). Color vision is typically remains intact as long as visual acuity is better than 20/40.

Attenuation of the retinal arterioles is the earliest observable sign in RP. Retinal pigmentary changes occur in the form of fine mottling or granularity with surrounding areas of atrophy. Later, stellate pigment hyperplasia may be noted at perivascular locations in the midperipheral retina. These hyperplastic formations are often referred to as "bone spicules."

As the disorder progresses, general atrophy of the RPE and choriocapillaris ensues, exposing the larger choroidal vessels. The optic nerve head is often normal in early RP, but may demonstrate a waxy yellow or pale appearance later. RP has a strong correlation with acquired optic disc drusen. The macula, like the optic nerve, is usually unaffected in the early stages, but in some forms of RP may demonstrate preretinal gliosis ("cellophane maculopathy"), cystoid macular edema or focal RPE defects. Additional findings in RP include pigment cells in the vitreous ("tobacco dust sign"), posterior vitreous detachment and posterior subcapsular cataracts.

Most patients with retinitis pigmentosa are myopic, and many have keratoconus as well. Electrodiagnostic testing in RP shows a significantly diminished scotopic ERG as well as an abnormal EOG and dark adaptometry.

PATHOPHYSIOLOGY
Retinitis pigmentosa is believed to stem from a genetic defect, which leads to a disturbance in the retinal pigment epithelium (RPE) and the breakdown of the photoreceptors' outer segment disc membranes. The resultant accumulation of metabolic by-products disrupts retinal function, and manifests as lipofuscin deposition, retinal gliosis, photoreceptor loss, choriocapillaris occlusion and RPE hyperplasia. These RPE changes compromise the blood-retina barrier, resulting in subretinal leakage and macular edema in later stages. Because the affected photoreceptor cells in most cases are rods, the patient typically experiences visual difficulty under dark conditions, as well as peripheral field constriction.

There are many forms of retinitis pigmentosa, and while most present with similar findings and outcome, some presentations are atypical. RP may be classified on the basis of inheritance pattern (autosomal dominant, autosomal recessive, X-linked, simplex, multiplex), age of onset (congenital, childhood onset, juvenile onset, adult onset), predominant photoreceptor involvement (rod-cone, cone-rod), or location of retinal involvement (central, pericentral, sectoral, peripheral).

MANAGEMENT
Since there is no known treatment for retinitis pigmentosa, management calls for prompt diagnosis and subsequent counseling to maintain quality of life.

Always obtain visual fields and electrodiagnostic testing to confirm the diagnosis of RP; order serology if the diagnosis is unclear or other disorders are suspected.

Most experts recommend a pedigree analysis of patients once RP has been diagnosed. This is critical to determine the exact inheritance pattern of the patient's condition. Individuals should know the risk for their progeny or other family members developing the disease.

Recommend genetic counseling to help the patient deal with these issues. Implement low-vision services as the disorder begins to affect visual function. Field-expansion devices, infrared blocking sun lenses and contrast enhancing filters may be helpful. Periodic optometric follow-up is also important. Perform visual fields several times a year, and evaluate for cataract or macular edema at least annually.

CLINICAL PEARLS

Most patients with RP are diagnosed in the second or third generation of life. Because of the insidious nature of the disorder, the earliest indicators are often objective findings rather than subjective complaints. Some presentations are extremely subtle, particularly in the early stages. Perform a critical evaluation on all patients presenting with complaints of nyctalopia or peripheral field loss.

The diagnosis of RP is often based upon appearance, but many "masqueraders" exist, including rubella retinopathy, syphilitic retinopathy, CMV retinopathy, toxoplasmosis, cancer-associated retinopathy, retinal drug toxicity secondary to thioridazine, chlorpromazine or chloroquine, pigmented paravenous retinochoroidal atrophy, and traumatic retinopathy.

Understandably, the untreatable progressive nature of retinitis pigmentosa is extremely unsettling for the patient and their loved ones; it is often beneficial to recommend psychological or family counseling early in the disease.

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