There are many rare and far flung retinal diseases which few of us will ever see in the office. One of these is Oguchi’s disease, a night blinding disorder in which patients can recover their sensitivity to dim light over several hours in darkness, only to lose it to a brief light exposure that hardly bleaches any visual pigment. The report in this issue by Yamamoto et al (p 1043) shows that the S cone electroretinogram (ERG) is normal in Oguchi’s disease, which distinguishes it electrophysiologically from some other types of stationary night blindness. This paper shows the value of clinical electrophysiology as a unique window into the pathophysiology of the retina, although perceptive readers may ask why Yamamoto et al talk about cones in a night blinding disorder. The fact is that most night blinding disorders do involve cones, and it can be hazardous to interpret retinal symptoms without an awareness of retinal physiology. What also may not be immediately …