1. A rare condition in which perception of blue and green becomes confused: Tritanopia is a result of the absence of the blue-sensitive pigment in the cone cells of the retina.
2. A visual defect in which the retina fails to respond to the color blue: Due to his tritanopia, Lord Allton, the artist, worked in black and white, avoiding the use of any warm tones in his paintings.
3. Etymology: from Greek tritos, "third" + anopia, "blindness". Based on the idea of not seeing a third of the color spectrum.