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. Author manuscript; available in PMC: 2013 Oct 21.
Published in final edited form as: J Vis. 2011 Mar 29;11(3):10.1167/11.3.20 20. doi: 10.1167/11.3.20

Figure 2.

Figure 2

Vertical horopter and the ground. Green and red spheres represent the left and right eyes, respectively. The green and red circles represent the sheared empirical meridians associated with empirical corresponding points. When the eyes are fixated parallel to the ground at infinity, the vertical horopter is a horizontal line extending to meet fixation at infinity. For a given eye height and inter-ocular distance, the optimal shear angle places the horopter in the ground plane. Due to Listing’s Law, the horopter remains in the ground when the eyes fixate the ground in the sagittal plane.