A relative afferent pupillary defect (RAPD) indicates reduced afferent light input from one eye relative to the other. RAPD is detected by the swinging flashlight test. A positive RAPD is seen in all of the following EXCEPT:

• A Optic neuritis of the right eye
• B Complete, post-ganglionic Horner syndrome affecting the left eye ✓
• C Dense vitreous haemorrhage reducing VA to hand movements in one eye
• D Severe glaucomatous optic neuropathy with advanced field loss in one eye

Explanation

RAPD reflects asymmetric afferent (sensory) input — any optic nerve or significant retinal pathology causing reduced light signal from one eye will produce RAPD in that eye. Optic neuritis, dense vitreous haemorrhage (reducing retinal illumination), and severe glaucomatous optic neuropathy all reduce afferent input and cause RAPD. Horner syndrome is a postganglionic SYMPATHETIC lesion affecting pupil dilation (miosis) without affecting the parasympathetic-driven light reflex arc — so there is no RAPD. RAPD requires an asymmetric lesion in the afferent arc (retina to pretectal nucleus).

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.