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Changes in Ricco’s Area with Background Luminance in the S-Cone Pathway

Redmond, Tony*; Zlatkova, Margarita B.; Vassilev, Angel; Garway-Heath, David F.§; Anderson, Roger S.*

doi: 10.1097/OPX.0b013e318278fc2b
Original Articles

Purpose The area of complete spatial summation (Ricco’s area) for achromatic stimuli has previously been shown to decrease with increased background luminance. A popular hypothesis is that such a phenomenon reflects increased center-surround antagonism within the receptive field of the retinal ganglion cell. We wished to investigate if similar changes in Ricco’s area occur with blue background luminance for the S-cone pathway, guided by the knowledge that the retinal ganglion cells with S-cone input do not display S-cone–mediated center-surround antagonism (S+/S-).

Methods Spatial summation functions were measured for four young healthy observers under S-cone pathway isolation by presenting blue test stimuli on a background consisting of intense fixed yellow (600 cd/m2) component in combination with a variable blue component (background range, 1.78 to 2.82 log S-Td). Ricco’s area was estimated by two-phase regression analysis.

Results All subjects demonstrated a notable decrease in Ricco’s area with increasing blue background luminance. On average, Ricco’s area decreased in size by 0.39 log units per log unit increase in blue background luminance.

Conclusions The change in Ricco’s area with the blue background component is not what one would initially expect given the known organization of S-cone–driven cells at the retinal level. Spatial reorganization by the suppressive surround of the receptive fields at a cortical level and a reduction in the contribution from S-cones with the lowest weights in the retinal receptive field periphery are among the possible mechanisms of the summation changes observed. These findings have implications for the design of clinical tests of the S-cone pathway.

*PhD, MCOptom

PhD

PhD DSci

§MD, FRCOphth

Vision Science Research Group, School of Biomedical Sciences, University of Ulster, Coleraine, Northern Ireland, United Kingdom (TR, MBZ, RSA); National Institute for Health Research (NIHR) Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom (TR, DFG-H, RSA); and Institute of Neurobiology, Bulgarian Academy of Sciences, Sofia, Bulgaria (AV).

Tony Redmond School of Optometry and Vision Sciences Cardiff University Maindy Rd Cardiff, CF24 4LU United Kingdom e-mail: RedmondT1@cardiff.ac.uk

© 2013 American Academy of Optometry