Tetartan

The “fourth” type of colorblindness (after Protan, Deutan & Tritan) that acts as an umbrella term for Tetartanomaly and Tetartanopia. Tetartan CVD affects the blue-yellow Opponent Channel (generally a weakening of the yellow stimulation).

There are no known congenital causes of Tetartan defects, though Cyanopsia can be loosely described as a Tetartan defect.