X-linked retinitis pigmentosa: clinical manifestations and diagnosis

X-linked retinitis pigmentosa (XLRP) is considered one of the most severe forms of retinitis pigmentosa (RP). It accounts for 6–20% of all disease cases. Nowadays, mutations in three genes (RP2, RPGR, and OFD1) have been identified to cause XLRP. Early symptoms are impaired night vision and/or visual field loss. The subsequent damage to the cones results in decreased visual acuity, photophobia and color vision disorders may also be observed. Ophthalmoscopy shows waxy optic disc pallor, vasoconstriction, foci of hypopigmentation and/or hyperpigmentation, sometimes in form of bone-spicule in the peripheral retina. Gradual reduction in amplitudes of light-adapted and dark-adapted electroretinograms (ERG) is specific for RP. Microperimetry reveals reduced average light sensitivity and paracentral ring scotoma despite normal or slightly decreased visual acuity. Optical coherence tomography (OCT) demonstrates destructed outer retinal layers, short-wavelength autofluorescence imaging shows a Robson-Holder ring. X-linked RP in females is almost always associated with notable variability in severity from asymptomatic cases to severe ones as in male patients. Night blindness is reported in 50% of female carriers of X-linked RP, visual acuity and amplitude of light-adapted and dark-adapted ERG are reduced in most cases. Fundus changes are observed in 87% of female carriers. A tapetal reflex is the most common. Foci of hypo- and hyperpigmentation, bone-spicule-like pigment clumping, extensive retinal pigment epithelial and choroidal atrophy are also reported. In the vast majority (63–79%) of female carriers of X-linked RP, short-wavelength autofluorescence images show radial patterns.