RPGR and retinitis pigmentosa 1: Finally, 30 Hz ERG were more preserved in pericentral RP patients (average: 24 μV) compared to typical RP patients (average: 7 μV in subjects with mutations in RHO [24]; 6 μV in subjects with mutations in USH2A [26]; 2 μV in subjects with mutations in RPGR [31]).