How is colour perceived: the visual pigments of human cones

Microspectrophotometric measurements obtained from individual receptor cells from the enucleated eyes of 8 normal observers and a known deuteranope are presented. In a sample of 147 receptors from seven normal eyes, 39 were rods with peak absorbance (lambda max) at 496 nm, 58 were long-wave with lambda max 558 nm, 45 were middle-wave cones with lambda max 531 nm and 5 were short-wave cones with lambda max 419 nm. There was evidence of bimodality in the distribution of both the long and middle-wave cones, but not in the rods, and a substantial difference in the mean spectral location of the long-wave cones was observed between two patients classified as normal trichromats. Psychophysical determinations of their relative sensitivity to long-wave fields showed a clear difference that proved, both in magnitude and direction, to be that required by the microspectrophotometric results. In a sample of 17 records from the eye of the deuteranope we recorded 5 rods, 2 short-wave cones and 10 long-wave cones, but no middle-wave cones. These results are concordant with psychological results obtained for the patient's remaining eye.