The Variability of Normal Trichromatic Vision and the Establishment of the “Normal” Range

A new Colour Assessment and Diagnosis (CAD) test has been developed and optimised to measure small changes in chromatic sensitivity. In addition the test quantifies the severity of redgreen and yellow-blue loss and classifies accurately even minimal congenital deficiencies. The technique employed makes use of dynamic luminance contrast (LC) noise to mask the detection of any residual LC signals in the test stimulus. The LC noise provides effective masking of LC signals without affecting the thresholds for detection of colour signals (Proc.R.Soc.Lond. B Biol.Sci. 258: 327-334, 1994). Chromatic discrimination thresholds are plotted in the CIE-(x,y) 1931 colour system. 125 normal trichromats have been tested in order to validate the CAD test and to derive a template that describes the range of normal colour discrimination sensitivity.