What is the horopter?

What is the horopter?

• A. The corneal reflection surface used in alignment testing.
• B. The boundary where objects yield diplopia.
• C. The theoretical surface of points that stimulate corresponding retinal points; objects off this surface can produce diplopia or suppression unless fusion is achieved.
• D. The cortical map of binocular neurons.

Answer: (C)

The horopter is the imaginary surface in space that consists of all points that stimulate corresponding retinal points in the two eyes. When an object lies on this surface, the images fall on corresponding locations on the retinas and the brain can fuse them into a single percept. Objects off the horopter create retinal disparities; depending on how large the disparity is, they may be fused within Panum’s fusional area to still appear single, or fail to fuse and produce diplopia, sometimes leading to suppression to avoid double vision. This definition captures both the idea of corresponding retinal points and the fusion limits that determine whether vision is single or double. The other options describe peripheral ideas (like corneal reflections or cortical maps) that aren’t what the horopter represents.

The horopter is the imaginary surface in space that consists of all points that stimulate corresponding retinal points in the two eyes. When an object lies on this surface, the images fall on corresponding locations on the retinas and the brain can fuse them into a single percept. Objects off the horopter create retinal disparities; depending on how large the disparity is, they may be fused within Panum’s fusional area to still appear single, or fail to fuse and produce diplopia, sometimes leading to suppression to avoid double vision. This definition captures both the idea of corresponding retinal points and the fusion limits that determine whether vision is single or double. The other options describe peripheral ideas (like corneal reflections or cortical maps) that aren’t what the horopter represents.