During a relative afferent pupillary defect (RAPD) examination using the swinging flashlight test, when the light is moved from the normal left eye to the abnormal right eye, which of the following is the CORRECT description of the pupillary response?

• A Both pupils constrict when light shines in the right eye
• B Right pupil constricts but left pupil dilates when light moves to the right eye
• C Both pupils dilate when light shines in the right eye (paradoxical dilatation) ✓
• D Right pupil dilates and left pupil remains unchanged when light moves to the right eye

Explanation

In RAPD, the afferent limb of the pupillary light reflex is reduced on the affected side. When the swinging flashlight moves from the normal eye to the affected eye, the pupillomotor stimulus entering the pretectal nuclei is weaker — both pupils DILATE compared to their constricted state (since the reflex is consensual and bilateral). This appears as 'paradoxical dilatation' of BOTH pupils. The efferent limb (CN III) is intact bilaterally, so both pupils respond symmetrically — RAPD is an afferent defect, not an efferent defect.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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