It is generally considered that the pupillary light threshold is slightly higher than the visual threshold. Although work done in this area has been limited, Schweitzer1 did publish an extensive study of this problem in 1956. He found that the pupillary and visual thresholds of the dark-adapted eye were identical when the entire retina was illuminated. When he stimulated small retinal areas, the threshold for a pupillary response was higher than the threshold for a visual response. His conclusion was that the luminous energy falling on larger areas was at least partially summated as far as the pupillary response was concerned.
Dr. Irene Loewenfeld2 had illuminated small areas of the retina, 40 degrees temporal to the fovea, in dark-adapted eyes. She found that the pupillary threshold was only 0.3 to 0.5 log unit higher than the visual threshold. She expressed the opinion that, depending upon whether and to
BURKE DW, OGLE KN. Comparison of Visual and Pupillary Light Thresholds in Periphery. Arch Ophthalmol. 1964;71(3):400–408. doi:10.1001/archopht.1964.00970010416019
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