Fig. 1. Reported age at onset of night blindness for patients with type I simplex-multiplex retinitis pigmentosa. (Adapted from Massoff RW, Boughman JA: Genetic analysis of subgroups within simplex and multiplex retinitis pigmentosa. In Cotlier E, Maumenee IH, Berman ER [eds]: New York, Alan R. Liss for the March of Dimes Birth Defects Foundation, BD:OAS 18[6]: 161–166, 1982)