Abstract
Abstract: :
Purpose: The photopic ERG can be used to assay cone function and it has been demonstrated that a spot stimulus can be used to isolate local retina1. In this study, we develop a photopic paradigm in order to derive a local macula response and in particular, investigate the effects of varying background luminance. Methods: Macular photopic ERGs were obtained under varying Ganzfeld backgrounds (0.2–200 cd.m–2) using a 14.5° spot target that varied in luminous energy from –0.7 to 4.2 log cd.s.m–2. Waveforms were collected every 2 sec with a DTL fibre over a bandpass of 1–1000 Hz (6 dB down) and digitised at 10 kHz. Up to 50 records were averaged for each response. The experimental setup adopted to measure the local response was a variant of that proposed by Jones et. al.1 Results: Increasing the Ganzfeld background resulted in a more prominent focal response that peaked at ∼ 20µV. This was supplanted by a marked response (∼ 130µV) due to scattered light. However, above a background of 20cd.m–2 the focal response declined. At low background light levels, the photopic hill was less pronounced demonstrating a plateau rather than the classical dip. Conclusions: Using sparse stimulation on a Ganzfeld background, a local macula ERG can be recorded that returns substantial amplitudes (∼20µV). Furthermore, as background light levels decline the photopic hill becomes less pronounced suggestive of altered ON and OFF interactions. 1. Jones R, King–Smith PE, Loffing DH & Gaynier FL. (1986) Clin Visual Sci 1: 153–160
Keywords: electroretinography: non–clinical • electrophysiology: non–clinical