A sensation of apparent depth among coloured objects placed at the same distance from the subject and viewed binocularly, when the pupils are eccentric to the achromatic axes or the visual axes do not coincide with the achromatic axes. This phenomenon is attributed to the retinal disparity created by the chromatic aberration of the eye. If the objects are red and blue (or green), the red appears closer than the blue (or green) in many people. Other people see the reverse impression and a few others do not see any apparent depth at all. The phenomenon can be enhanced, eliminated or reversed by using prisms or pinhole pupils placed in different regions of the pupil. If the pinhole pupils are decentred symmetrically temporally in front of the natural pupils, the red object will appear closer than the blue (positive chromostereopsis) and if they are decentred nasally, the blue object appears closer than the red (negative chromostereopsis). Apparent depth is eliminated when the pinholes are centred on the achromatic axes or when using prisms of appropriate power and direction. Syn. chromatic stereopsis; colour stereoscopy. See longitudinal chromatic aberration; chromatic parallax.
Millodot: Dictionary of Optometry and Visual Science, 7th edition. © 2009 Butterworth-Heinemann