visual pathway & field

• Visual pathway


  The anatomical pathway by which electrical signals generated by the retina are sent to the brain
• Components of the retina

  • Sensory retina
  • Neural retina
  • Retinal Pigmented Epithelium
  • Three ordered neurons
  • Phototransduction
  • Graded potential
  • Action potential
  • Nerve impulse
• Optic nerve


  • From axons of ganglion cells, gathered into a bundle of nerves
  • Myelinated and covered with fats
  • Around 50-60mm or not more than 6 cm long
  • Has four parts: intraocular, intraorbital, intracanalicular, intracranial
• Optic chiasm


  Nasal fibers of each eye cross the midline to join the temporal fibers of the contralateral eye
• Terminal points of optic tract axons

  • Lateral geniculate body (visual perception)
  • Suprachiasmatic (circadian rhythm)
  • Pretectum (pupillary light reflex)
  • Superior colliculus (eye movement)
• Lateral geniculate body


  • Small swelling under the pulvinar of the thalamus
  • Has 6 layers
• Optic radiations


  1. Carry fibers from superior retinal quadrants through parietal lobe (dorsal "where" pathway)

  2. Carry fibers from inferior retinal quadrants through temporal lobe via Meyers' loop (ventral "what" pathway)
• Visual cortex


  • Posterior portion of occipital lobe
  • Lies along calcarine fissure
  • Made up of six layers
  • Processing center for form, movement, and color
• Visual field refers to the area of space in which objects are visible during steady fixation in one direction
• Monocular visual field


  • Central visual field (30 degrees)
  • Peripheral visual field (100 degrees laterally, 60 degrees medially, 60 degrees upward, 75 degrees downward)
• Physiologic scotoma/blind spot is located 15 degrees temporally representing the optic nerve head
• Kinds of visual field tests

  • Kinetic perimetry (detection of moving targets)
  • Static perimetry (detection of stationary targets)
• Confrontation test


  Tests if the patient has functional temporal fibers and nasal retinal fibers
• Amsler grid test


  Assesses the macula and central visual field within 10 degrees of fixation
• Tangent screen test


  Measures the central 30 degrees fixation under well illumination
• Goldmann perimeter


  Self-illuminated projection perimeter that can control fixation, stimulus size/intensity, and background luminance
• Octopus perimeter


  Measures static and kinetic perimetry, including the G-program (30-degree field for glaucoma) and M-program (10-degree field for macula)
• Visual field charting detects loss of central and peripheral vision and provides a map of visual field loss
• Types of visual field defects

  • Anopia (loss of vision in one eye)
  • Hemianopsia/hemianopia (loss of one half of the vertical visual field)
  • Quadrantanopsia (loss of one fourth of the visual field)
  • Scotoma (abnormal blind spot)
• Types of scotomas


  • Central scotoma (blind spot in the line of sight)
  • Paracentral scotoma (loss of vision within 10 degrees of the focal point)
  • Centrocecal scotoma (scotoma running from the center to the blind spot)
• Types of scotomas by shape

  • Arcuate scotoma (arc-shaped)
  • Scintillating scotoma (arc-shaped, shifting peripherally, experienced during migraine aura)