Convergence Micropsia

Convergence micropsia is a form of micropsia, the perceptual distortion in which objects appear smaller than they actually are, that occurs specifically when a person's eyes are converged, angled inward toward each other, more than the actual distance to the viewed object requires. The effect appears most often during stereoscopy, particularly when viewing autostereograms such as Magic Eye pictures, where moving the image closer to the eyes increases how much they must converge and correspondingly shrinks the perceived size of the depicted objects. It can also occur when a stereogram or autostereogram is viewed with the eyes deliberately crossed rather than held parallel, again making objects appear smaller than when viewed normally, and the same distortion could in principle also be produced by viewing a scene through base-out prisms, which force the eyes into a similarly excessive convergence.