Another term for dichromasia; a condition of color vision where only two of the three types of color receptors are functional.
From Greek 'dicha' (two) and 'chroma' (color), plus the suffix '-sy' (condition or state). This is a variant form of 'dichromasia' used in ophthalmic and color vision research.
About 1 in 12 men have red-green dichromasy but most don't realize it until adulthood—and interestingly, some research suggests certain birds and insects have four types of color receptors, giving them a 'tetrachromatic' vision we can barely imagine.
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