VISUAL SYSTEM 2

  1. Common Descriptive Terminology:
  • Visual field: The total area in which objects can be seen in the periphery of vision while the eye is focused on a central point.
  • Monocular: Relating to, affecting, or using only one eye.
  • Binocular: Involving the use of both eyes.
  • Scotoma: A partial loss of vision or a blind spot in an otherwise normal visual field.
  • Anopia: Total absence of vision, with specific types based on the region of visual field affected (e.g., hemianopia).
  • Hemianopia: Blindness over half the field of vision.
  • Quadrantanopia: Blindness in a quarter of the visual field.
  • Homonymous: Visual field defects that are the same in each eye (e.g., loss on the left side in both eyes).
  • Heteronymous: Visual field defects that affect opposite sides in the two eyes (e.g., bitemporal hemianopia).
  • Macular sparing: A condition where the central vision is preserved despite other areas of vision loss.
  1. Visual Pathway:
  • Retina to Optic Nerve: Light information is transformed into neural signals by the retina and transmitted through the optic nerve.
  • Optic Chiasm: Fibers from the nasal half of each retina cross to the opposite side, while those from the temporal half do not cross.
  • Optic Tract to Lateral Geniculate Nucleus (LGN): Signals are relayed to the LGN, which sorts them by eye of origin and type of information (motion vs. detail and color).
  • Optic Radiations: Fibers leave the LGN and pass through the posterior limb of the internal capsule to reach the primary visual cortex in the occipital lobe.
  • Visual Cortex to Association Areas: The primary visual cortex processes basic visual information which is then sent to association areas for further interpretation.
  1. Visual Field Deficits:
  • Central Scotoma: A blind spot in the center of the visual field, often linked to optic nerve damage or macular degeneration.
  • Monocular Visual Loss: Complete vision loss in one eye, possibly due to optic nerve or severe retinal damage.
  • Retinal Transient Ischemic Attack: Temporary vision loss in one eye, suggesting vascular issues like carotid artery stenosis.
  • Visual Auras and Fortification Scotomas: Seen in migraine, characterized by flickering lights or geometric patterns.
  • Bitemporal Hemianopia: Loss of the outer half of the visual field in both eyes, typically due to a pituitary tumor affecting the optic chiasm.
  • Nasal Hemianopia: Loss of the nasal field in one or both eyes, often due to damage at the optic chiasm.
  • Homonymous Hemianopia: Loss of the same half of the visual field in both eyes, indicating damage behind the optic chiasm.
  • Sectoranopia and Quadrantanopia: Partial field loss, indicating localized lesions in the optic tract or radiations.
  • Homonymous Hemianopia with Macular Sparing: Typical of cortical strokes affecting the visual cortex but sparing the macular region due to robust blood supply.