What test primarily distinguishes a phoria from a tropia?

What test primarily distinguishes a phoria from a tropia?

• A. Alternating cover test
• B. Unilateral cover test
• C. Maddox rod testing
• D. NPC

Answer: (B)

The main idea is that a tropia is a visible, manifest misalignment, while a phoria is latent and only shows up when fusion is broken. The unilateral cover test is the test that best reveals this distinction by isolating one eye and checking for a realignment response of the other eye when the cover is placed and removed. If a constant deviation exists (a tropia), you'll see the eyes move to re-fixate or drift when the cover is applied or removed, indicating a misalignment that is present even with one eye occluded. If no such movement occurs during this test, the deviation is latent and would only appear when fusion is disrupted in a different way, such as with an alternating cover test. In contrast, the alternating cover test disrupts fusion repeatedly to reveal a phoria, and Maddox rod testing and the NPC test assess different aspects of binocular vision (angle of deviation under dissociation and convergence, respectively) rather than definitively distinguishing latent from manifest deviations.

The main idea is that a tropia is a visible, manifest misalignment, while a phoria is latent and only shows up when fusion is broken. The unilateral cover test is the test that best reveals this distinction by isolating one eye and checking for a realignment response of the other eye when the cover is placed and removed. If a constant deviation exists (a tropia), you'll see the eyes move to re-fixate or drift when the cover is applied or removed, indicating a misalignment that is present even with one eye occluded. If no such movement occurs during this test, the deviation is latent and would only appear when fusion is disrupted in a different way, such as with an alternating cover test.

In contrast, the alternating cover test disrupts fusion repeatedly to reveal a phoria, and Maddox rod testing and the NPC test assess different aspects of binocular vision (angle of deviation under dissociation and convergence, respectively) rather than definitively distinguishing latent from manifest deviations.