Summary
The visual pathway transmits signals from the retina to the visual cortex. It consists of the retina, optic nerve, optic chiasm, optic tract, lateral geniculate nucleus, optic radiations, and visual cortex. Lesions of the visual pathway may lead to visual disturbances or visual loss, the pattern of which can assist in determining the exact location of the lesion. Unilateral visual field loss indicates a prechiasmal pathology, while bilateral visual field loss indicates a chiasmal or retrochiasmal pathology. Retinal diseases mostly cause central or paracentral scotomas. Prechiasmal damage to the visual pathway usually involves the optic nerve (e.g., optic neuritis, optic atrophy, AION, papilledema) and may manifest with anopia or a centrocecal scotoma. Damage in the region of the optic chiasm is most commonly due to compression by a pituitary adenoma or craniopharyngioma and manifests with bitemporal heteronymous hemianopsia (lesions of the crossing fibers) or binasal hemianopsia (lesions of noncrossing fibers). Retrochiasmal visual pathway damage occurs in the region of the optic tract, lateral geniculate nucleus, optic radiation, or visual cortex and is most commonly due to cerebral ischemia/hemorrhage, tumors, or trauma. It usually manifests with homonymous hemianopsia or homonymous quadrantanopsia.
Overview
The visual pathways transmit signals from the retina to the visual cortex (striate cortex, brodmann area 17).
Structure | Characteristics | Lesions | Causes |
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Retina |
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Optic nerve |
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Optic chiasm |
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Optic tract |
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Optic radiations |
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Visual cortex |
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Unilateral visual field loss → pathology mainly in front of the optic chiasm. Bilateral visual field loss → pathology mainly in or behind the optic chiasm
Remember that the Meyer Loop transmits the signal from the Lower retina, Looping around the inferior horn of the Lateral ventricle.
References:[1][2]
Prechiasmal visual pathway damage
Prechiasmal damage to the visual pathway mainly involves the optic nerve.For retinal diseases see table above.
Optic nerve
Optic neuritis
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Definition: inflammation of the optic nerve
- Retrobulbar neuritis: inflammation of the retrobulbar part of the optic nerve
- Papillitis: inflammation of the intrabulbar part of the optic nerve
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Etiology
- Most common cause: multiple sclerosis
- Infections
- Toxic
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Clinical features
- Vision impairment: blurry vision, sudden vision loss, color blindness, visual field defects (e.g., central scotoma)
- Retrobulbar pain (increased pain caused by eye movements)
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Diagnostics
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Ophthalmoscopy
- Retrobulbar neuritis: normal ophthalmoscopic finding
- Papillitis: poorly defined papilla, hyperemia, hemorrhage at the border of the papilla
- Visual evoked potential (VEP)
- Neurological examination
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Ophthalmoscopy
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Treatment
- High-dose treatment with glucocorticoids
- Corresponding treatment in the case of multiple sclerosis
Multiple sclerosis is the most common cause of optic neuritis!
Optic atrophy
- Definition: irreversible loss of axons in the optic nerve
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Etiology
- Most common causes: optic neuritis, glaucoma
- Vascular
- Hydrocephalus, orbital/intracranial lesion
- Hereditary: Leber optic atrophy, Krabbe disease, autosomal-dominant optic atrophy
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Clinical features:
- Vision impairment: blurry vision, color blindness, visual field defects (e.g., central scotoma)
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Diagnostics
- Fundoscopy
- Perimetry
Anterior ischemic optic neuropathy (AION)
- Definition: segmental or generalized infarction of the anterior part of the optic nerve
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Etiology
- Nonarteritic form due to atherosclerosis (NAION)
- Arteritic form due to giant cell arteritis (AAION)
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Clinical features
- Sudden unilateral loss of vision
- Wedge-shaped and altitudinal visual field defects
- AAION: other symptoms of giant cell arteritis
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Diagnostics
- Fundoscopy
- Laboratory findings
- AAION: temporal artery biopsy
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Treatment
- AAION: immediate high-dose systemic glucocorticoids
- NAION: trial of hemodilution and systemic glucocorticoid therapy
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Prognosis
- Typically poor: permanent loss of vision
- Involvement of the other eye is common during the course of the disease.
Immediate high-dose glucocorticoid treatment is essential in AAION!
Papilledema
- Definition: swelling of optic disc due to elevated intracranial pressure
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Etiology:
- Hypertensive emergency
- Idiopathic intracranial hypertension (pseduotumor cerebri)
- Intracranial tumors (e.g., medulloblastoma)
- Hydrocephalus
- Cerebral abscess
- Hypervitaminosis A
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Clinical features
- Acute: usually asymptomatic, can present with loss of visual acuity due to enlargement of blind spot
- Chronic (rare): impaired vision, can cause visual field defects and blindness
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Diagnostics
- Fundoscopy
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Acute:
- Edematous, poorly defined, prominent optic disc with blurry margins
- Widened blind spot
- Radial hemorrhage around the disc margin
- Later stages of disease: optic atrophy possible
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Acute:
- Cranial CT or MRI to detect cause of increased intracranial pressure
- Fundoscopy
Damage in the region of the optic chiasm
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Etiology
- Most commonly: compression by pituitary adenoma (prolactinoma), craniopharyngioma, meningioma, aneurysms of the internal carotid artery
- Demyelination, multiple sclerosis
- Trauma
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Pathophysiology
- Medial lesion (e.g., pituitary adenoma) → temporal visual field defects
- Lateral lesion (e.g., aneurysm of the internal carotid artery) → nasal visual field defects
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Clinical features
- Visual field defects/impaired vision: most commonly bitemporal heteronymous hemianopsia
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Treatment
- Depending on the cause
- Neurosurgical
- Pharmacological
- Depending on the cause
Retrochiasmal visual pathway damage
- Definition: damage in the region of the optic tract, lateral geniculate nucleus, optic radiation, or visual cortex
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Etiology
- Cerebral ischemia/hemorrhage
- Tumors
- Trauma
- Other causes
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Clinical features
- Visual field defects/impaired vision: most commonly homonymous hemianopsia and homonymous quadrantanopsia
- Diagnostics