# Lab2 - Vision Science III - Ocular Motility & Binocular...

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Vision Science III - Ocular Motility & Binocular Vision Lab 2 - The Apparent Fronto-Parallel Plane (AFPP) Horopter THE THEORETICAL HOROPTER A horopter is a set of points in space where an object must be placed if it is to stimulate exactly corresponding points on the two retinas. The horopter also represents a set of points that cause zero disparity on the retinas. If a visual line is projected out of one eye, and the corresponding visual line is projected out of the other eye, the intersection of these is a point on the horopter. In theory, the horopter is an arc that lies on a circle that goes through the fixation point and the nodal points of the two eyes. This theoretical horopter is known as the Vieth-Müller Circle ; each different fixation distance has its own its own Vieth-Müller Circle. The Vieth-Müller Circle (theoretical horopter) is based on certain geometric assumptions about the eyes. These are: Each retina may be represented by a perfect circle. Corresponding points are evenly space across the nasal and temporal retinas of each eye. Both retinas are the same size and corresponding points are perfectly matched for their locations in the two eyes. These are reasonable assumption for model eyes. Based on these assumptions, if you project corresponding visual lines out of the two eyes and plot their intersection points, they should form a circle—the Vieth-Müller Circle. This geometry has some interesting characteristics, as illustrated in Figure 1. Since all points on this circle are projections from a common chord (PD), the binocular convergence angle between the eyes to any point on the circle is always the same (Angle θ ). The alternate angles at Point O formed by the crossing of the visual axes are equal, and two similar triangles are created-—triangles FON 1 and PON 2 . Then Angle

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## This note was uploaded on 06/07/2011 for the course OPTO. 101 taught by Professor Bill during the Spring '08 term at Indiana East.

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Lab2 - Vision Science III - Ocular Motility & Binocular...

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