Visual Pathway Flashcards
Parts of optic nerve (& lengths)
47-50 mm in length
1. Intraocular = 1mm
2. Intra orbital = 25-30 mm
3. Intracanalicular = 6-9 mm
4. Intracranial = 10-16 mm
Features of distal optic nerve lesions
- Marked loss of vision & complete blindness (on affected side)
- Direct (ipsilateral) & consensual (contralateral) light reflex -ve
- Near accommodation reflex +ve
Causes of distal optic nerve lesions
- optic atrophy
- traumatic avulsion of optic nerve
- indirect optic neuropathy
- ischemic optic neuropathy
- acute optic neuritis
Features of proximal optic nerve lesions
- Ipsilateral blindness
- Contralateral hemianopia
- Direct (affected) & consensual (contralateral) light reflex -ve
- Near reflex +ve
Causes of intrinsic (thickening of chiasma) chiasmal lesion
- Gliomas
- Multiple sclerosis
Causes of extrinsic (compressive lesion) chiasmal lesion
- Pituitary adenoma
- Craniopharyngiomas
- Meningioma
Other causes of chiasmal lesion
- metabolic
- toxin
- traumatic
- inflammatory condition
Affected parts in anterior chiasmal syndrome
- Ipsilateral optic nerve fiber
- Contralateral inferonasal fiber
Affected parts in middle chiasmal syndrome
Decussating fibers in body of chiasma
Affected parts in posterior chiasmal syndrome
Caudal fibre
Anterior chiasmal syndrome leads to
Junction scotoma
Middle chiasmal syndrome leads to
Bitemporal hemianopia
Posterior chiasmal syndrome leads to
- Paracentral bitemporal field defects
- Homonymous hemianopia on contralateral side
Features of lateral chiasmal lesion
Binasal hemianopia
Causes of lateral chiasmal lesion
- Distension of 3rd ventricle
- Atheroma of carotid/post communicating arteries
Intrinsic causes of optic tract lesion
- demyelinating disease
- infarction
Extrinsic causes of optic tract lesion
- pituitary adenomas
- craniopharyngiomas
- tumours of optic thalamus
- large aneurysm of sup cerebellar/post cerebral arteries
Features of optic tract lesion
- Incongruous homonymous hemianopia
- Contralateral hemianopia pupillary response – Wernicke’s reaction
- Optic disc changes: temporal pallor on lesion side & bowtie atrophy on other side
- Ipsilateral third nerve palsy
- hemiplegia
Features of lateral geniculate nucleus lesions
- Homonymous hemianopia
- Normal pupillary reflex
- Optic disc pallor
Causes of optic radiation lesion
- vascular occlusion
- tumors
- trauma
- temporal lobectomy for seizures
Superior quadrantic hemianopia
(pie in the sky)
Inferior fibres are involved in temporal lobe lesion
Inferior quadrantic hemianopia (pie on the floor)
Superior fibres are involved in parietal lobe lesion
Features of visual cortex lesions
- Congruous homonymous hemianopia
- Congruous homonymous macular defect
- Bilateral homonymous hemianopia
- Bilateral homonymous macular defect
