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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.
Visual fields tests will delineate chiasmal syndromes because the missing fields will not cross the midline. Junctional scotomas classically show ipsilateral optic disc neuropathy with contralateral superotemporal defects. Bitemporal hemianopia with or without central scotoma is present if the lesions have affected the body of the chiasm. A ...
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 ...
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.
Binasal (either inferior or superior) quadrantanopia, also known as Nerurkarian field defects affects either the upper or lower inner visual quadrants closer to the nasal cavity in both eyes. Bitemporal (either inferior or superior) quadrantanopia affects either the upper or lower outer visual quadrants in both eyes. [citation needed]
It creates a bottom-up saliency map of the visual field to guide attention or eye gaze to salient visual locations. [35] [clarification needed] Hence selection of visual input information by attention starts at V1 [36] along the visual pathway. Visual information then flows through a cortical hierarchy. These areas include V2, V3, V4 and area ...
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.
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