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E. M. Garland, J. P. Comerford, F. Thorn, A. Moskowitz; Physiological Variability Among Observers With Clinically Normal Color Vision. Invest. Ophthalmol. Vis. Sci. 2007;48(13):3813.
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© ARVO (1962-2015); The Authors (2016-present)
The Medmont C-100 Colour Vision Tester uses heterochromatic flicker photometry (HFP) to reveal differences in cone populations among color deficient observers. It is also believed to be capable of quantifying variations in the cone population among clinically normal color observers. We investigated whether differences in Medmont C-100 settings are correlated with hue discrimination using the Farnsworth-Munsell 100-Hue Test under conditions of decreased illumination. The decreased illumination could facilitate further exaggeration of color discrimination ability in the color normal population.
One hundred color normal observers were screened using the Medmont C-100. Of that group, 34 were selected for further testing: those whose settings were outside the normal range (experimental group, N=17) and a control group (N=16). These 34 observers each made ten consecutive settings with the Medmont C-100 and performed the FM 100-Hue using approximately one-quarter the usual illumination provided by a Macbeth Easel lamp.
The mean (SD) Medmont C-100 setting for the experimental group was -1.14 (0.37). The mean (SD) Medmont C-100 setting for the control group was -0.04 (0.25), significantly different from the experimental group (p<0.001). The mean (SD) FM 100-Hue error score was 72 (34) for the experimental group and 71(31) for the control group. For one female observer, the mean Medmont C-100 setting was +1.3; her FM 100-Hue error score was 300. Based on her family history, she was identified as a likely carrier of a color vision deficiency.
Among clinically normal color observers, variations in Medmont C-100 settings are not accompanied by variations in FM 100-Hue error scores. We believe that heterochromatic flicker photometry as used in the Medmont C-100 isolates the Magnocellular pathway. In contrast, the FM 100-Hue is likely to reflect activity in the Parvocellular pathway. We hypothesize that the FM 100-Hue test reflects the action of gain control mechanisms (Neitz et al., 2002) to a greater extent than does the Medmont C-100 test.
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