Basic Human Neuroanatomy
A Clinically Oriented Atlas 
Case 47 Answers

1.  Where in the visual pathway would you localize the lesion in this case (optic nerve, optic chiasma, optic tract, optic radiations, or occipital cortex)?

Left optic nerve (II), near the optic disc

2.  What is an afferent pupillary defect (Marcus Gunn pupil), what is its anatomical basis, and what localizing significance does it have?

Paradoxical dilation of a pupil ipsilateral to an optic nerve lesion, when the light is shined back onto that pupil during the “swinging flashlight test”.  An APD is due to an impaired direct light reflex with an intact consensual light reflex.  It localizes the lesion to the ipsilateral optic nerve (or widespread retinal disease).

3.  What side of the nervous system is involved in this case?  What specific structure(s) is involved by the pathologic process?

Left optic nerve (II), near the optic disc

4.  In general, what type of pathologic process was involved in this case?

Vascular – Ischemic optic neuropathy (ION) involving the superior branch of the left central retinal artery (embolic vs inflammatory vs vasospasm)

5.  What diagnostic procedure(s) would you undertake at this point?

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