RAPD

Question 1

What causes an RAPD? [1]
Give two specific causes [2]

Answer 1

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
- retina: detachment
- optic nerve: optic neuritis e.g. multiple sclerosis

Question 2

Describe the pathway of the pupillary light reflex [2]

Answer 2

Pathway of pupillary light reflex
afferent: retina → optic nerve → lateral geniculate body → midbrain

efferent: Edinger-Westphal nucleus (midbrain) → oculomotor nerve

Question 3

Describe the results seen in swinging light reflex in an afferent lesion in RAPD [1]
Why [1]

Answer 3

If there is damage to the afferent pathway (retina or optic nerve) of one eye, the pupil of that affected eye will abnormally dilate when a light is shone into it.
- This is because the consensual pupillary relaxation response from the healthy eye will dominate.