The Visual System Flashcards
The left brain receives visual information from ___, and the right brain receives visual informaton from ___.
The left brain receives visual information from the right visual fields of both eyes, and the right brain receives visual informaton from the left visual fields of both eyes.
Movement of visual information through the optic tract (diagram)
Lateral geniculate nucleus
Region of the thalamus that receives information from a visual field.
One on each side, carrying contralateral visual field information.
Monocular visual deficit
Due to either ocular pathology or optic nerve (pre-chiasm) pathology
Homonymous visual deficit
ie, one visual field in both eyes
Posterior to the optic chiasm, in the optic tract, LGN, optic radiation(s), or occipital lobe (on the side contralateral to the homonymous deficit
Quadrantanopia
A visual deficit in one quadrant in both eyes
Caused by lesions affecting an individual optic radiation or individual bank of the calcarine cortex on the contralateral side
A superior quadrantanopia localizes to the contralateral inferior radiation and/or inferior bank of the calcarine cortex.
An inferior quadrantanopia localizes to the contralateral superior radiation and/or superior bank of the calcarine cortex.
Homonymous hemianopia
Incongruous visual field deficits that are on the same side in each eye (homonymous) but of different shapes in each eye
Caused by a contralateral optic tract lesion, contralateral LGN lesion, or lesion in the contralateral occipital lobe
Isolated lesions in the optic tract or lateral geniculate nucleus are rare in practice.
Homonymous hemianopia with macular sparing
Due to infarction of one occipital lobe from stroke in the posterior cerebral artery territory
May be due to the macula receiving some blood supply from the middle cerebral artery and/or the macula being bilaterally represented since it is at the center of vision and, therefore, does not fall into one “field.”
Bitemporal hemianopia
Loss of both lateral visual fields.
This is the result of damage to the optic chiasm, causing loss of peripheral vision on both sides.
Ipsilateral central scotoma and contralateral superior temporal quadrantanopia
This combination is called a “junctional scotoma,” and it occurs when the optic nerve is affected at its junction with the chiasm
This produces an ipsilateral central scotoma (from optic neuropathy) and contralateral superior temporal quadrantanopia because the inferior nasal fibers (representing the superior temporal quadrant) loop anteriorly into the most distal portion of the contralateral optic nerve after crossing before proceeding posteriorly.
In general, monocular vision loss is classified as . . .
In general, monocular vision loss is classified as acute or nonacute, and painful or painless.
Sudden and painless monocular visual loss is generally ___ in etiology
Sudden and painless monocular visual loss is generally vascular in etiology
Painful monocular visual loss often occurs with. . .
. . . acute angle closure glaucoma and optic neuritis.
Signs of optic neuropathy
Blurred vision centrally (central scotoma or cecocentral scotoma if it extends to the blind spot), decreased color vision, decreased visual acuity, and an afferent pupillary defect.
Optic neuritis sign
Usually on top of optic neuropathy signs
Optic nerve swelling may be visible on fundoscopy (unless the inflammation is more posterior in the optic nerve (retrobulbar), in which case the optic nerve may appear normal).