• Clinical science

Disorders of the visual pathway

Overview

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.
Optic nerve
  • Transmits visual information from the ipsilateral retina to the brain
  • Afferent limb of pupillary reflex and accomodation reflex
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
Optic tract

Lateral geniculate nucleus (LGN)

  • Transmits information of the
    • ipsilateral, nasal visual field
    • contralateral, temporal visual field
  • Projects to primary visual cortex via optic radiations
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 infromation from the upper retina
    • Projects to the cuneus gyrus
Visual cortex

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
  • Etiology
  • Clinical features
  • 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
  • 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!

Optic atrophy

Anterior ischemic optic neuropathy (AION)

  • Definition: segmental or generalized infarction of the anterior part of the optic nerve
  • Etiology
  • 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: temporal artery biopsy
  • Treatment
  • 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

Damage in the region of the optic chiasm

The triad of bitemporal visual field defects, unilateral or bilateral reduction in visual acuity, and optic atrophy is referred to as chiasmal syndrome!

Retrochiasmal visual pathway damage