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The visual pathway consists of structures that carry visual information from the retina to the brain.Lesions in that pathway cause a variety of visual field defects. In the visual system of human eye, the visual information processed by retinal photoreceptor cells travel in the following way:
Lesions in the pathway cause a variety of visual field defects. The type of field defect can help localize where the lesion is located (see figure). A lesion in the optic nerve of one eye causes partial or complete loss of vision in the same eye, with an intact field of vision in other eye.
Hemianopsia, or hemianopia, is a visual field loss on the left or right side of the vertical midline. It can affect one eye but usually affects both eyes. Homonymous hemianopsia (or homonymous hemianopia) is hemianopic visual field loss on the same side of both eyes. Homonymous hemianopsia occurs because the right half of the brain has visual ...
Medical examination of the optic nerve with an ophthalmoscope may reveal a swollen optic nerve, but the nerve may also appear normal. Presence of an afferent pupillary defect, decreased color vision, and visual field loss (often central) are suggestive of optic neuritis. Recovery of visual function is expected within 10 weeks.
The function of the feedback from the visual cortex back to the LGN is unknown. The optic radiation is activated during working memory tasks. [3] The optic radiations are usually unilateral and commonly vascular in origin. Field defects, therefore, develop abruptly, in contrast to the slow progression of defects associated with tumors.
Macular sparing can be determined with visual field testing.The macula is defined as an area of approximately + 8 degrees around the center of the visual field. [3] During examination, vision in an area of greater than 3 degrees must be preserved for a patient to be considered to have macular sparing because there is involuntary eye movement within 1 to 2 degrees.
The visual field defects can vary, and while some patients may experience immediate maximal vision loss, others may notice a gradual worsening. The optic disc in these cases can appear swollen, sometimes accompanied by hemorrhages. [ 41 ]
Cortical blindness-Cortical blindness is the total or partial loss of vision in a normal-appearing eye caused by damage to the brain's occipital cortex. [7] Retrobulbar neuritis- Retrobulbar neuritis cause of visual loss with normal fundus but there will be relative afferent pupillary defect (RAPD) and abnormal visually evoked responses. [8]