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Disorders of the visual pathway

Last updated: July 26, 2021

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 of the visual pathways

The visual pathways transmit signals from the retina to the visual cortex (striate cortex, brodmann area 17).

Structure	Characteristics	Lesions	Causes
Retina	Cones and rods transform light into visual signals, which are projected to the brain via the optic nerve.	Central scotoma occurs in case of macula involvement Paracentral scotoma Occurs in case of macula involvement with foveal sparing (e.g., hydroxychloroquine/chloroquine maculopathy) Seen as concentric rings of hypopigmentation and hyperpigmentation on the macula (“bull's eye maculopathy”)	Diseases of the retina Retinal detachment Retinal vessel occlusion
Optic nerve	Transmits visual information from the ipsilateral retina to the brain Afferent limb of pupillary reflex and accommodation reflex	Ipsilateral blindness (anopia),scotoma Centrocecal scotoma: loss of vision in the fovea centralis region and a blind spot Pupillary light reflex: loss of afferent limb → absent direct pupillary light reflex	Optic neuritis (MS) Optic atrophy Retinal vessel occlusion Anterior ischemic optic neuropathy Papilledema
Optic chiasm	Fibers from nasal part of the retina cross to contralateral side Fibers from the temporal part of the retina do not cross to the contralateral side	Middle lesions (crossing fibers) → bitemporal heteronymous hemianopsia Bilateral lesions (non-crossing fibers) → binasal hemianopsia	Pituitary adenoma Craniopharyngioma Parasellar aneurysm of the internal carotid artery Meningioma
Optic tract	Transmits information of the ipsilateral, nasal visual field contralateral, temporal visual field Projects to lateral geniculate nucleus, pretectal area, superior colliculi, suprachiasmatic nuclei	Contralateral homonymous hemianopsia	Middle cerebral artery (MCA) infarction
Lateral geniculate nucleus (LGN)	Transmits information of the ipsilateral, nasal visual field contralateral, temporal visual field Projects to primary visual cortex via optic radiations	Contralateral homonymous hemianopsia	Infarction of either the MCA or PCA ^[1] Sometimes MCA → anterior choroidal artery Posterior cerebral artery → lateral choroidal artery
Optic radiations	Anterior/lateral bundle in Meyer loop Passes through the temporal lobe in close proximity to the inferior horn of the lateral ventricle Transmits information of the superior visual field from the lower retina Projects to the lingual gyrus Posterior/medial bundle Located in the parietal lobe, passes through the internal capsule Transmits information of the inferior visual field from the upper retina Projects to the cuneus gyrus	More common than optic tract or LGN lesions Anterior/lateral/inferior bundle (Meyer loop) Contralateral upper homonymous quadrantanopsia (“pie in the sky”) Posterior/medial/superior bundle Contralateral lower homonymous quadrantanopsia (“pie on the floor”)	MCA infarction Upper quadrantanopsia indicates temporal lobe lesion Lower quadrantanopsia indicates parietal lobe lesion
Visual cortex	Located in the calcarine sulcus of the occipital lobe	Contralateral homonymous hemianopsia with macular sparing	Posterior cerebral artery (PCA) infarction

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.

Optic nerve and visual pathway Overview of visual field defects Bitemporal hemianopsia Right homonymous hemianopsia Homonymous hemianopia with macular sparing

References:^[2]^[3]

Scotoma and anopia

Scotoma

An area within an otherwise normal visual field where vision is temporarily or permanently reduced or absent

Blind spot: a physiologic scotoma in the visual field formed by axons leaving the eye to form the optic nerve (optic papilla) temporal to the center of the visual field
Central scotoma: scotoma in the center of an eye's visual field
Paracentral scotoma: scotoma near the center of an eye's visual field
Centrocecal scotoma: scotoma running from the center to the blind spot of an eye's visual field
Arcuate scotoma: an arc-shaped scotoma that starts at the blind spot and courses over the center of an eye's visual field
Scintillating scotoma: an arch-shaped scotoma that starts centrally and shifts peripherally, that is typically experienced during an migraine aura (especially in retinal migraines)
- Perception of an arch-shaped area of decreased vision
- Moves from paracentral to peripheral vision
- Flickering lights appearing in zigzag patterns
- Usually bilateral
- Typically lasts for 15–30 min ^[4]
- May be followed by headache or, less commonly, occur concomitantly with headache.
- See “Migraine” for more information about diagnostics and treatment.

Types of scotomas Perimetry

Anopia

A larger visual field defect that affects a quarter, half, or the entire vision of an eye

Unilateral anopia: vision loss in one eye
Hemianopia: vision loss in one half of the visual field separated by the vertical midline
- Bitemporal heteronymous hemianopia: vision loss at the outer (temporal) half of the visual field of both eyes
- Binasal hemianopia: vision loss at the inner (nasal) half of the visual field of both eyes
- Homonymous hemianopia: vision loss of one half of the visual field on the same side in both eyes
- Macular sparing: macular vision is preserved despite adjacent visual field loss
Quadrantanopia: vision loss in a quarter of the visual field of both eyes

Unilateral vision field loss indicates a disorder of a structure anterior to the optic chiasm. Bilateral visual field loss indicates a pathology at or posterior to the optic chiasm.

Overview of visual field defects Bitemporal hemianopsia Right homonymous hemianopsia

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

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
Etiology
- Most common cause: multiple sclerosis
- Infections
- Toxic
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)
Diagnostics
- Swinging-flashlight test: relative afferent pupillary defect
- Ophthalmoscopy
  - Retrobulbar neuritis: normal ophthalmoscopic finding
  - Papillitis: poorly defined papilla, hyperemia, hemorrhage at the border of the papilla
- Visual evoked potential (VEP)
  - Assess conduction disorders of the optic nerve
  - In acute retrobulbar neuritis: mainly potential attenuation or deficit (by a conduction block)
  - After previous retrobulbar neuritis: possible delay in latency
- Cranial magnetic resonance imaging (cMRI)
- Neurological examination
Treatment
- High-dose treatment with glucocorticoids
- Corresponding treatment in the case of multiple sclerosis
Prognosis
- Visual improvement usually starts after 2 weeks.
- Visual acuity is usually good after 1 year.
- Frequent persistence of deficits in color vision and contrast sensitivity.
- Further prognosis depends on the potential existence of an underlying disease.

Multiple sclerosis is the most common cause of optic neuritis!

Fundus in optic neuritis

Optic atrophy

Definition: irreversible loss of axons in the optic nerve
Forms: morphological differentiation
- Primary/simple optic atrophy: the optic disc is pale or chalky white and sharply demarcated.
- Secondary/complex optic atrophy: the optic disc is pale or grey, poorly defined, and prominent.
- Glaucomatous optic atrophy (see glaucoma)
Etiology
- Most common causes: optic neuritis, glaucoma
- Vascular
- Hydrocephalus, orbital/intracranial lesion
- Hereditary: Leber optic atrophy, Krabbe disease, autosomal-dominant optic atrophy
Clinical features:
- Vision impairment: blurry vision, color blindness, visual field defects (e.g., central scotoma)
Diagnostics
- Fundoscopy
  - Primary form: pale devitalized papilla, sharply demarcated
  - Secondary form: pale devitalized papilla, prominent with a blurry margin
- Perimetry

Anterior ischemic optic neuropathy (AION)

Definition: segmental or generalized infarction of the anterior part of the optic nerve
Etiology
- Nonarteritic form due to atherosclerosis (NAION)
- Arteritic form due to giant cell arteritis (AAION)
Epidemiology
- NAION: peak incidence between 50 and 70 years of age, but also observed in younger patients
- AAION: almost always after 60 years of age
Clinical features
- Sudden unilateral loss of vision
- Wedge-shaped and altitudinal visual field defects
- AAION: other symptoms of giant cell arteritis
Diagnostics
- Fundoscopy
  - Acute: edematous, poorly defined optic disc, usually sectoral; pale or hyperemic; radial hemorrhage around the disc margin
  - Late course of the disease: optic atrophy
- Laboratory findings
  - AAION: ↑ ESR and CRP
  - NAION: normal ESR and CRP
- AAION: temporal artery biopsy
Treatment
- AAION: immediate high-dose systemic glucocorticoids
- NAION: trial of hemodilution and systemic glucocorticoid therapy
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! Arteritic anterior ischemic optic neuropathy

Papilledema

Definition: swelling of optic disc due to elevated intracranial pressure
Etiology:
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
Diagnostics
- Fundoscopy
  - 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
- Cranial CT or MRI to detect cause of increased intracranial pressure

Papilledema in intracranial hypertension Bilateral papilledema

Neovascularization of retina and uvea

Damage in the region of the optic chiasm

Etiology
- Most commonly: compression by pituitary adenoma (prolactinoma), craniopharyngioma, meningioma, aneurysms of the internal carotid artery
- Demyelination, multiple sclerosis
- Trauma
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
Clinical features
- Visual field defects/impaired vision: most commonly bitemporal heteronymous hemianopsia
- Sometimes chiasmal syndrome: triad of bitemporal visual field defects, unilateral or bilateral reduction in visual acuity, and optic atrophy
Treatment
- Depending on the cause
  - Neurosurgical
  - Pharmacological
Prognosis
- Complete regression of impaired vision/visual field defects is possible with timely treatment.

Bitemporal hemianopsia

Retrochiasmal visual pathway damage

Definition: damage in the region of the optic tract, lateral geniculate nucleus, optic radiation, or visual cortex
Etiology
- Cerebral ischemia/hemorrhage
- Tumors
- Trauma
- Other causes
Clinical features
- Visual field defects/impaired vision: most commonly homonymous hemianopsia and homonymous quadrantanopsia
- Optic atrophy in cases with a CN III lesion
Diagnostics
- Perimetry
- Imaging: CT, MRI
Prognosis
- Usually no regression of visual field defects

Right homonymous hemianopsia

References

JD Trobe. Neuro-ophthalmology. Elsevier ; 2008
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Wallace DJ. Antimalarial Drugs in the Treatment of Rheumatic Disease. In: Post TW, ed. UpToDate. Waltham, MA: UpToDate. https://www.uptodate.com/contents/antimalarial-drugs-in-the-treatment-of-rheumatic-disease.Last updated: October 23, 2017. Accessed: November 8, 2018.
Luco C, Hoppe A, Schweitzer M, Vicuña X, Fantin A. Visual field defects in vascular lesions of the lateral geniculate body. J Neurol Neurosurg Psychiatry. 1992; 55 (1): p.12-5.