An anomaloscope or Nagel's anomaloscope is an instrument used to test for color blindness. It is used to measure quantitative and qualitative anomalies in colour perception. It can be used to determine whether a person is a tritanope, dichromat or achromatop. The apparatus was invented by the German ophthalmologist and physiologist Willibald A. Nagel (1870–1911) who named it "anomaloskop" in 1907.
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Anomaloscope Wikipedia(Text) CC BY-SA