Patients with amblyopia will often experience the ___________ phenomenon with a Snellen acuity chart.

• A. Crowding phenomenon
• B. Diplopia
• C. Perceptual filling-in
• D. Ocular misalignment

Answer: (A)

When testing with a Snellen chart, the main issue in amblyopia is the crowding effect. The affected eye has trouble recognizing a letter when it’s flanked by other letters, because the visual system’s ability to isolate fine spatial details is reduced. This makes acuity appear worse in crowded conditions than when letters are isolated, which is a hallmark finding in amblyopic eyes. Diplopia isn’t typical here because suppression usually prevents two distinct images from being seen at once. Perceptual filling-in involves completing missing parts of a scene, not the interference from neighboring letters, and ocular misalignment is a separate issue that may accompany amblyopia but doesn’t explain the crowding-driven acuity drop.