Relative afferent pupillary defect (Marcus-Gunn pupil)

Also known as the Marcus-Gunn pupil, a relative afferent pupillary defect is found by the 'swinging light test'.
It is caused by a lesion anterior to the optic chiasm i.e. optic nerve or retina.

Causes:
 Retina: detachment
 Optic nerve: Optic Atrophy, Optic neuritis (e.g. multiple sclerosis)


Pathway of pupillary light reflex:
 Afferent: retina → optic nerve → lateral geniculate body → midbrain
 Efferent: Edinger-Westphal nucleus (midbrain) → oculomotor nerve.

Examination: 'swinging light test'

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