Onset and clinical features


RP is typically diagnosed in young adulthood, but the age of onset may range from early childhood to the mid 30s to 50s. Photoreceptor degeneration has been detected as early as age of six years even in patients who remain asymptomatic until young adulthood.

    • Clinical features:


Since rod function is primarily affected, the most common initial symptoms of typical RP (rod-cone RP) include night blindness (nyctalopia), followed by visual field defects with preservation of central visual acuity until the late stages of the disease. Severe visual impairment occurs by ages 40 to 50 years.

    • Nyctalopia:


The earliest symptom in RP is most commonly night blindness, which is considered a hallmark of the disease. It is usually observed during childhood. Patients complain of defective dark adaptation: difficulty seeing in dim illumination (night, dusk or fog conditions), tendency to trip easily or bump into objects when in poor lighting.

    • Visual loss:


Progressive visual field constriction (typically presenting by the teenage age) is another hallmark of RP. The visual field defects may initially present as small asymptomatic scotomas that progress to form a "tunnel" configuration as the disease advances. The rate of progression is slow but relentless. The visual field loss is usually symmetric and expands more rapidly outward, with a slower progression inward toward the central field.

Typical rod-cone RP is associated with preservation of the central vision acuity until the later stages of the disease. In some cases, the onset of central visual impairment is earlier (e.g. atypical RP or presence of associated factors, such as cystoid macular edema and cataracts). Visual acuity can remain normal. Reading impairment and difficulties in undertaking daily activities are typically seen when visual acuity falls below 0.5 (20/40).

    • Color vision defects:


Color vision in patients with typical rod-cone RP remains good until the central vision is affected at a level of 20/40 or worse. A deficiency in blue cone function (acquired tritanopia) is characteristic of advanced RP. Mild blue-yellow axis color defects are common, however most patients do not complain of significant difficulties with color perception.

    • Photophobia:


Photophobia is common mostly in patients with cone-rod RP, especially in the later stage of the disease.

    • Photopsia:


RP patients report seeing flashes of light (photopsia) described as small, shimmering, blinking lights or coarse sparkling grains similar to the symptoms of an ophthalmic migraine. In contrast to ophthalmic migraine, the photopsia in RP is rather continuous than episodic. Photopsia is a common complain in patients with cone-rod RP in their mid-peripheral field of vision, adjacent to areas of scotoma. Photopsias may decrease over the years, as scotomas become denser.

    • Other clinical manifestations:


RP patients frequently develop a form of cataract (up to 50% of adult RP patients). It is typically observed between 20 and 39 years of age, and the incidence is increasing with age. Keratoconus is rare but it may reduce visual acuity and increase glare. Loss of contrast sensitivity and eye fatigue are frequently reported. Myopia varies among distinct subtypes of RP, an increased prevalence being noted in X-linked RP.

    • Fundus findings:


Fundus findings depend on the stage of retinal deterioration. The earliest observed changes in the fundus are fine dust-like granularity of the retinal pigment epithelium (RPE), with normal associated vasculature and pigmentary mottling ("moth-eaten" pattern). However, visible funduscopic changes may be absent in the initial stages. The middle stage shows a more patchy loss of the RPE and the beginning of retinal vessel attenuation. Arteriolar narrowing, waxy palor of the disc, cystoid macular edema and bone spicule-like pigment changes are consistent with long-standing retinal and RPE degeneration in advanced RP.

    • Syndromic RP:


Approximately 20-30% of RP patients have associated non-ocular disease that includes more than 30 different syndromes. Among the most common syndromic forms of RP are Usher syndrome, Refsum disease, Bassen-Kornzweig syndrome, Bardet-Biedl syndrome and Batten disease.