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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:
The other major retino–cortical visual pathway is the ... areas of the visual field corresponding to a contralateral lesion in the primary visual cortex; however ...
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.
If a lesion only exists in one unilateral division of the optic radiation, the consequence is called quadrantanopia, which implies that only the respective superior or inferior quadrant of the visual field is affected. If both divisions on one side of the brain are affected, the result is a contralateral homonymous hemianopsia.
Visual agnosia occurs after damage to visual association cortex or to parts of the ventral stream of vision, known as the "what pathway" of vision for its role in object recognition. [6] This occurs even when no damage has been done to the eyes or optic tract that leads visual information into the brain; in fact, visual agnosia occurs when ...
Vascular and neoplastic (malignant or benign tumours) lesions from the optic tract, to visual cortex can cause a contralateral homonymous hemianopsia. Injury to the right side of the brain will affect the left visual fields of each eye. The more posterior the cerebral lesion, the more symmetric (congruous) the homonymous hemianopsia will be.
Visual pathway lesions From top to bottom: 1. Complete loss of vision, right eye 2. Bitemporal hemianopia 3. Homonymous hemianopsia 4. Quadrantanopia 5&6. Quadrantanopia with macular sparing. Proper function of the visual system is required for sensing, processing, and understanding the surrounding environment.
A lesion affecting one side of the temporal lobe may cause damage to the inferior optic radiations (known as the temporal pathway or Meyer's loop) which can lead to superior quadrantanopia on the contralateral side of both eyes (colloquially referred to as "pie in the sky"); if the superior optic radiations (parietal pathway) are lesioned, the ...