How Local Is the Multifocal ERG

Abstract

Abstract: : Purpose: To investigate the relative scatter contributions to local multifocal ERG responses. Methods: The local multifocal ERG response consists of a local a lateral and a scatter component. However the balance of these contributions to the local responses is unknown. By creating areas of low or high sensitivity to scatter it is possible to estimate the level of neighbouring scatter contributions on the local mfERG response. Seven healthy controls underwent a series of experiments using a fixed mfERG stimulus paradigm with an inactive 3^rd and 4^th ring. These inactive regions were presented at three fixed luminance levels (black, grey and white). The relative amplitude of surrounding active rings was measured and compared for normal stimulation and at these fixed luminance levels. Results: There was on average a 15% increase in response amplitude in local areas when the surrounding area was fixed at a low (black) luminance. At mean (grey) luminance response amplitudes displayed a less than a 1% variation in responses and at full (white) luminance there was a 20% decrease in response amplitudes. Conclusions: There is a significant scatter contribution to the local response from surrounding areas. These results indicate that at least 20% of the local responses is reflective of activity outside the area of interest.

Keywords: electroretinography: clinical • electrophysiology: clinical • clinical research methodology