Advanced Binocular Vision (ABV) Exam 2 Practice 2026 - Free ABV Practice Questions and Study Guide

Aniseikonia is the mismatch in perceived image size between the two eyes. This size difference makes it hard for the brain to fuse the two images into a single view, which disrupts binocular fusion and reduces stereoacuity. It can arise from anisometropia (different refractive errors in the two eyes) or from optical magnification differences produced by corrective lenses. While diplopia can occur if fusion fails dramatically, the defining issue here is the interocular size disparity itself. Stereoacuity—the ability to perceive depth—suffers when fusion is imperfect due to aniseikonia. NPC is unrelated, as it refers to convergence distance.