Name the two types of cover testing.

• A. Alternate
• B. Alternate and unilateral
• C. Unilateral
• D. Binocular

Answer: (B)

Cover testing checks how the eyes align when fusion between them is disrupted. There are two main approaches you’ll use. The unilateral cover test involves covering one eye at a time and watching the other eye for movement as the cover is applied and removed; a movement of the eye that is uncovered indicates a tropia, a constant misalignment. The alternate cover test switches the occluder between the two eyes rapidly, breaking fusion without letting either eye settle on a target; any drift observed during these alternations reveals a phoria, a latent misalignment that only appears when fusion is disrupted. In short, unilateral cover testing detects tropias, while alternating cover testing detects phorias.