How does anisometropia affect stereoacuity?

• A. It improves stereoacuity
• B. It often reduces stereoacuity due to suppression of the worse eye or avoidance of fusion
• C. It only affects accommodation but not stereo
• D. It has no effect on fusion

Answer: (B)

Anisometropia creates unequal image quality between the two eyes, so the brain tends to suppress the image from the more ametropic eye to avoid diplopia. That suppression reduces or eliminates the binocular input needed to compute depth from small disparities, which is what stereoacuity depends on. So stereoacuity is often reduced when anisometropia is present, especially if suppression has led to amblyopia. If the anisometropia is properly corrected (ideally with contact lenses to minimize blur differences), stereoacuity can improve, though long-standing suppression may limit recovery in some individuals. It does not improve stereoacuity on its own, it does affect fusion, and it does have an impact on binocular fusion.