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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