Fig. 4. Electroretinogram (ERG) responses from normal subject and four obligate carriers of sex-linked retinitis pigmentosa. Patient (Pt) 15, age 39; Pt 8, age 41; Pt 4, age 51; Pt 22, age 70. Stimulus onset is designated by vertical hatched lines for columns 1 and 2 and vertical shock artifacts for column 3. Cornea-positivity is upward deflection. Arrows in column 3 designate cone b-wave implicit times. (From Berson EL, Rosen JB, Simonoff EA. Electroretinographic testing as an aid in detection of carriers of X-chromosome-linked retinitis pigmentosa. Am J Ophthalmol 1979;87:460.)