Contribution of post-receporal cells to the cone a-wave of the human electroretinogram in congenital stationary night blindness and autoimmune-like retinopathy.

In normal subjects the later part of the cone a-wave to a brief flash increases in amplitude after 50-100 ms darkness due to a contribution from secondary hyperpolarising cells. We recorded these responses along with clinical ON and OFF ERGs in patients with inner retinal dysfunction to see if this part of the a-wave is affected. Patients with autoimmune-like retinopathy and CSNB2 had abnormal ON and OFF responses but the a-wave increased in amplitude in the dark as in normals. Conversely, the OFF-response was normal in CSNB1 but the a-wave did not increase in the dark. Contrary to expectation these results show some hyperpolarising cell function in autoimmune-like disease and CSNB2 and some OFF-pathway abnormality in CSNB1. The a- and d-wave are needed to assess OFF-pathway function.