Historical Review of Stereoscopic Fundus

axes), one can construct a curved surface on which any point would be focused or mapped to precisely corresponding points on the two re t i n a s . This surface is the horopter, often simplified as a curved line in the horizontal plane (Figure 3-2). For example, a point 4 degrees to the right of fixation on the horopter would be imaged on each retina precisely four degrees to the left of each fovea (point A in Figure 3-2). Any points lying in front of this surface would not fall on anatomically corre s p o n d i n g points but would be shifted temporally on each retina. Any points beyond the horopter would be shifted nasally, again to noncorresponding retinal points. The further from the horo p t e r, the greater the anatomical retinal disparity. The complex neural circuitry associated with vision is capable of synthesizing depth information from these disparate images, giving the sensation of stereopsis. Stereo Fundus Photography: Principles and Technique 81