The Stiles–Crawford effect of the first kind and the full-field electroretinogram (ERG)

Abstract

Electroretinography (ERG) can be used to quantify the directional sensitivity of the retina to incident stimuli. We have developed a rapid technique to derive a global measurement of the Stiles–Crawford effect of the first kind (SCE I) using the full-field flash ERG using artificial pupils. Three opaque haptic contact lenses were designed to direct stimuli along the photoreceptor axes with a single central aperture or obliquely through double apertures of equivalent area (4.5 mm²) separated horizontally by 3.0 and by 5.5 mm. ERGs recorded using an HK loop electrode to a series of white flashes ranging from sub-threshold to 2000 cd s/m² were presented in a ganzfeld bowl. Sensitivity was compared using the luminance:response functions for the ERG a-wave and b-wave amplitudes. The b-waves of the ERGs showed a shift in sensitivity between the central mid and outer apertures requiring stronger flashes for threshold, semi-saturation and saturation for the more peripheral apertures. The ERG a-waves did not demonstrate a significant sensitivity shift. Small apertures are suitable for generating oblique stimulation of photoreceptors for ERG recordings. The method described gives a global measure of the SCE I that may be useful when time or cooperation is limited. Apertures reduce the available light and positioning is less precise than with Maxwellian view systems. Thus, physical apertures in contact lenses may not be suitable for positioning stimuli on small retinal regions.

Keywords:

• electroretinogram
• ERG
• Stiles–Crawford effect of the first kind (I)
• directional sensitivity of the retina
• photoreceptors
• directional sensitivity

Acknowledgements

This research was supported by the Royal Society of Edinburgh, International Exchange Programme. We thank Dr R. Hamilton and Dr A. Al Abdlsaead for assistance in modelling the b-wave and Mr MJ Courtney of Cantor & Nissel Ltd for assistance with the lens design.