Figure 3. Electroretinogram studies. Shown are scotopic and photopic ERG responses from one affected family member (4200105; left column) and a normal control (right column). The cone-derived responses in the affected family member revealed neither detectable single flash photopic response nor flicker 30 Hz response(C, D). Assessment of the rod-derived functions by the scotopic single flash test show a detectable but markedly abnormal respond, (A, B). These findings are consistent with CORD.