Contrast Sensitivity of the Human Retina

Contrast thresholds (ΔL/L) were measured from the fovea to the far periphery at 2 degree intervals, along 12 meridians for a total of 1350 data points. The test spot, 10 minutes of arc in diameter, was presented against a 0.85 mL background in the Harms perimeter. Contrast senstivity decreases (i.e. thresholds increase) in all directions from the fovea out to a distance of 10 degrees. A broad region of equal sensitivity was found to extend from 10 degrees to 20 degrees in the superior, inferior and nasal visual fields and to 35 degrees in the temporal field. We call this region of equal sensitivity the “plateau.” Beyond the edge of this plateau, contrast sensitivity decreases at a uniform rate to the edge of the visual field. The size of the plateau remains constant in photopic, mesopic and scotopic vision (at background luminances from 8.5 × 10−1 to 8.5 × 10−5 mL).