A patient has a large-angle esotropia and fusing none at distance. The 3-prism-dioptre (3Δ) base-out test for microtropia shows a movement suggesting the existence of which sensory anomaly?

• A Diplopia with normal retinal correspondence
• B Suppression scotoma at the fovea of the deviating eye
• C Anomalous retinal correspondence (ARC) ✓
• D Amblyopia ex anopsia without any sensory adaptation

Explanation

The 3Δ base-out test is used to detect microtropia and anomalous retinal correspondence (ARC). In a normal eye, a 3 prism dioptre base-out prism induces a refixation movement (version followed by fusional vergence). In an eye with ARC where the non-foveal retinal point has taken up the corresponding point, the same 3Δ prism does not produce a refixation movement because the deviating eye's fovea is already used to receiving non-corresponding stimulation. This lack of refixation movement ('no reflex') indicates either a deep suppression scotoma or ARC. ARC allows binocular function despite manifest deviation in microtropia.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.