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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 ...
Homonymous denotes a condition which affects the same portion of the visual field of each eye. [4]Homonymous inferior quadrantanopia is a loss of vision in the same lower quadrant of visual field in both eyes whereas a homonymous superior quadrantanopia is a loss of vision in the same upper quadrant of visual field in both eyes.
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.
According to Pollock et al. (2010) stroke is the main cause of specific visual impairment, most frequently visual field loss (homonymous hemianopia, a visual field defect). Nevertheless, evidence for the efficacy of cost-effective interventions aimed at these visual field defects is still inconsistent. [53]
In bitemporal hemianopsia, vision is missing in the outer (temporal or lateral) half of both the right and left visual fields. Information from the temporal visual field falls on the nasal (medial) retina. The nasal retina is responsible for carrying the information along the optic nerve, and crosses to the other side at the optic chiasm. When ...
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.