title: Senescent changes in photopic spatial summation.
abstract: Previous studies have demonstrated an inverse relation between the size of the complete spatial summation area and ganglion cell density. We hypothesized that if this relation is dynamic, the spatial summation area at 6° nasal would expand to compensate for age-related losses of retinal ganglion cells but not in the fovea where age-related loss in ganglion cell density is not significant. This hypothesis was tested by measuring contrast thresholds with a series of Gabor patches varying in size. The spatial summation area was defined by the intersection of the segments of a two-branched, piece-wise linear function fitted to the data with slopes of -0.5 and 0 on a plot of log threshold vs. log area. Results demonstrate a 31% increase in the parafoveal spatial summation area in older observers with no significant age-related change in the fovea. The average foveal data show a significant increase in thresholds with age. Contrary to the foveal data, age comparisons of the parafoveal peak contrast thresholds display no significant difference above [corrected] the summation area. Nevertheless, as expected from the increase in summation area, expressing the parafoveal thresholds as contrast energy reveals a significant difference for stimuli that are smaller than the maximal summation area.
authors.affiliation: Department of Ophthalmology and Vision Science, University of California, Davis, USA. mmalania@mail.utexas.edu
authors.forename: Maka
authors.initials: M
authors.lastname: Malania
authors.forename: Frédéric
authors.initials: F
authors.lastname: Devinck
authors.forename: Kenneth
authors.initials: K
authors.lastname: Knoblauch
authors.forename: Peter B
authors.initials: PB
authors.lastname: Delahunt
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Hardy
authors.forename: John S
authors.initials: JS
authors.lastname: Werner
mesh_terms: D000328:Adult; D000368:Aged; D000375:Aging / Q000502:physiology*; D055253:Color Vision / Q000502:physiology*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D010775:Photic Stimulation; D012165:Retinal Ganglion Cells / Q000502:physiology*; D012684:Sensory Thresholds; D013028:Space Perception / Q000502:physiology*; D055815:Young Adult