anomaloscope

anomaloscope 

An instrument for testing colour vision in which the observer is required to match one-half of a circular field which is illuminated with yellow with a mixture of green and red in the other half. The yellow half can be varied in brightness, while the other may be varied continuously from red to green. A certain combination of the red and green mixture is considered normal, and variations from that mixture indicate anomalous colour vision. With this instrument one can distinguish between a protanope and a protanomal and between a deuteranope and a deuteranomal. Syn. Nagel anomaloscope. Some anomaloscopes also test for blue-yellow colour vision deficiencies, e.g. Pickford-Nicholson anomaloscope. See defective colour vision; Rayleigh equation.