ERGs and PERGs from 3 patients with rod-cone dystrophy-retinitis pigmentosa. (A) In this patient, whose visual acuity is 20/20, there is almost complete extinction of both rod and cone ERGs, but PERG is normal, suggesting that central retinal function is not significantly compromised. (B) This patient has relatively mild visual acuity reduction (20/30), but marked PERG PSO reduction. Generalized cone function, although markedly abnormal, is better preserved than in patient in part A, but abnormal PERG confirms central retinal dysfunction. (C) In this patient, with visual acuity of 20/120, both maximal and cone ERGs show slightly better preservation than in part A patient, but PERG is nondetectable and visual acuity is severely reduced. Complementary nature of ERG and PERG in assessment of global and central retinal function is demonstrated. (D) Normal control.