Chapter contents
Overview
Sensory transduction
Central course
Primary visual cortex
Retinal deficits
Optic nerve damage
Chiasm damage
Damage posterior to chiasm
| Cranial Nerve II - Optic Nerve | Page 11 of 11 |
Clinical Correlation -
Damage Posterior to the Optic Chiasm, cont'd
Damage to the optic radiation
Fibers of the optic radiation are considerably more spread out than those of the optic tract. As a result, damage normally only occurs to a portion of the geniculocalcarine tracts.
Figure 2-11a. Damage to the optic radiation.
Damage to the fibers of Meyer's loop and/or damage to the temporal lobe portion of the optic radiation results in loss of input from the inferior half (superior visual field) of both contralateral hemiretinas (superior quadrantanopia).
Damage to the fibers of the parietal lobe portion of the geniculocalcarine tract results in a loss of input from the superior half (inferior visual field) of both contralateral hemiretinas (inferior quadrantanopia).
Macular sparing
Often lesions in the optic radiation or primary visual cortex do not produce a complete loss of vision from the appropriate visual field but leave some central vision intact. This is due to the fact that input from the center of the retina (the macula) is spread over a large portion of the optic radiation and primary visual cortex.
For example, damage to one side of the primary visual cortex below the calcarine fissure will often produce loss of vision from the inferior half (superior visual field) of both contralateral hemiretinas with macular sparing (superior quadrantanopia with macular sparing).
Figure 2-11b. Macular sparing.
