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

Abstract

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.

Incremental and decremental L- and M-cone-driven ERG responses: I Square-wave pulse stimulation

“…It is the M-cone stimulus offset that produces components (N Md and P Md ) more typical of the a-and b-waves associated with luminance onsets. This on-off response inversion observed in the M-cone ERG is a novel finding and represents a departure from documented ERG response behavior where, up to now, a-and b-waves have invariably been considered a feature of retinal responses to the onset of a light stimulus and d-waves the responses to the termination of a stimulus [1,[4][5][6][7][8]. This on-off response inversion for the M-cone ERG is also replicated for sawtooth temporal stimulation [Kremers et al (this volume)].…”

“…Independent here means that the emission spectrum of one stimulus cannot be obtained by a linear combination of the emission spectra of the other stimuli. Hence, the stimulator used in these experiments contains four types of LED (blue, green, amber, and red) with peak wavelengths (± half-bandwidth at half-height) at 460 nm (15), 514 nm (20), 590 nm (8), and 635 nm (10), respectively. The spectral characteristics, chromaticities, and luminances of each class of LED were calibrated using a PR650 spectrophotometer (Photo Research Inc., Chatsworth, California, USA).…”

“…While the ERG response waveform is ultimately dependent upon the spatial, temporal and spectral characteristics of the stimulus (as well as the adaptational state of the observer), the transient onset of a light increment stimulus typically elicits a response that comprises a corneal negative a-wave and a positive b-wave, while stimulus offset generates a d-wave [1][2][3]. These components are thought to be the result of complex interactions between photoreceptor activity and postreceptoral contributions from second-order neurons such as on-and off-bipolar cells, horizontal cells, and Müller glial cells [1,[4][5][6][7][8]. This dependency on contributions from multiple retinal elements highlights the utility of the ERG as a means by which normal and pathological physiology can be studied in the human retina.…”