The relative numbers of long-wavelength-sensitive to middle-wavelength-sensitive cones in the human fovea centralis

The determination of the relative numbers of different cone types in the human retina is fundamental to our understanding of visual sensitivity and color vision; yet direct measurements which provide this basic information have not previously been made for all cone types. Here we present a model which links the detection of a test light of small dimension to the number of cones contributing to detection of the light. We selectively isolated either the long-wavelength-sensitive ( L) or the middle-wavelength-sensitive ( M) cones, by choosing combinations of wavelengths of adapting backgrounds and tests to favor detection by the cone class of interest. Our model was applied to the detection functions measured for six color normal observers to obtain estimates of the relative numbers of L to M cones. Our estimates ranged between 1.46 and 2.36 for our observers with a mean value near two L cones for every M cone in human fovea centralis.