The area of complete scotopic spatial summation enlarges with age

Brooke E. Schefrin, Michelle L. Bieber, Ryan McLean, John S Werner

Research output: Contribution to journalArticlepeer-review

37 Scopus citations


The maximal area of complete scotopic spatial summation (Ricco's area) was determined for 50 subjects ranging in age from 19 to 87 yr. Increment thresholds were measured for 10-ms, 520-nm circular test lights of varying diameters that were superimposed and concentric with a 10°, 640-nm circular background. The test lights were imaged in Maxwellian view along the horizontal meridian, 6° nasal from a foveal fixation point. The results demonstrate a statistically significant enlargement of Ricco's area with age. The average angular subtenses of Ricco's areas for the ten youngest (mean = 26 yr) and ten oldest (mean = 75 yr) observers were approximately 48 and 69 arc min, respectively. Model simulations based on a series of optical transfer functions of the eye and varying degrees of intraocular light scatter for younger and older observers show that preneural factors cannot account for these results. Therefore changes in neural mechanisms must be invoked to explain the enlargement in the size of Ricco's area under scotopic conditions.

Original languageEnglish (US)
Pages (from-to)340-348
Number of pages9
JournalJournal of the Optical Society of America A: Optics and Image Science, and Vision
Issue number2
StatePublished - 1998
Externally publishedYes

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Computer Vision and Pattern Recognition


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