# 31 - Optic nerve CN II

# Optic nerve CN II

© SPMM Course 
11. 
Cranial nerves 
Olfactory nerve CN I 
 Only sensory nerve to have no thalamic relay 
 Unilateral anosmia should raise the suspicion of a lesion affecting the olfactory nerve filaments, 
bulb, tract, or stria. 
 Because the cortical representation for the smell in the piriform cortex is bilateral, a unilateral 
lesion distal to the decussation of the olfactory fibers (i.e. temporal/ uncinate) causes no olfactory 
impairment. 
 Frontal meningiomas can cause unilateral anosmia. 
 Head injury is probably the most common cause of disruption of the olfactory fibers Hyposmia is 
an early feature of Parkinson’s disease and Alzheimer’s dementia and may precede motor and 
cognitive signs respectively. 
 Impaired sense of smell is seen in some patients at 50% risk of Parkinsonism. 
Optic nerve CN II 
Syndrome 
Lesion 
Unilateral one eye blindness 
Lesion anterior to optic chiasm e.g. optic nerve itself or retina 
Bitemporal hemianopia 
Optic chiasmatic lesion e.g. cranipharyngioma, pineal tumors 
Homonymous hemianopia – left 
Lesions of the right sided optic tract, lateral geniculate body, optic 
radiations and striate cortex (any retro chiasmatic structure) 
Homonymous hemianopia – right 
Lesions of the left retro chiasmatic structures 
Enlargement of the blind spot 
Any process causing disc swelling 
Superior quadrantanopia 
Optic irradiation lesion at temporal lobes of contralateral side 
Inferior quadrantanopia 
Optic irradiation lesion at parietal lobes of contralateral side 
Cortical blindness 
Occipital cortex lesions 
 Hemianopia is a field defect covering roughly half of the field. Vertical hemianopia can be nasal or 
temporal. Horizontal or altitudinal hemianopia can be superior or inferior. If only one-fourth of 
the field is affected, this is called quadrantanopia. 
 Bilateral field defects are homonymous when they affect the identical portion of vision in both 
visual fields 
 Funnel vision: In patients with organic visual system defect, the visual field projected at 2 metre 
distance is larger than the field at 1 m. This is seen in glaucoma, retinitis pigmentosa, post 
papilledema optic atrophy, bilateral occipital infarcts with macular sparing. 
 Tunnel vision refers to the absence of disparity between 2m and 1m fields on confrontation test. 
The presence of patchy spirals of field loss is seen in hysteria or malingering. 
 Cortical blindness often results from simultaneous bilateral posterior cerebral artery occlusion. 
Patients often have a bilateral homonymous hemianopia with the small central field around the 
point of fixation (macular sparing or keyhole vision) or complete blindness. Occasionally, patients 
with cortical blindness deny their visual defect (Anton's syndrome). 
 The following testing is appropriate for optic nerve: