Maxwell's spot

Maxwell’s spot

A reddish spot seen in the centre of a visual field when a white surface is viewed by a normal (i.e., not colour impaired) observer through a dichroic filter transmitting red and blue lights. The spot is regarded as an entoptic phenomenon due to preferential absorption of blue light in macular pigment. The most common form is symmetrical, circular, and comprised of three concentric zones: a central reddish spot, surrounded in turn by a clear ring of background colour and a reddish halo.
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