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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:
In neuroanatomy, the optic radiation (also known as the geniculocalcarine tract, the geniculostriate pathway, and posterior thalamic radiation) are axons from the neurons in the lateral geniculate nucleus to the primary visual cortex. The optic radiation receives blood through deep branches of the middle cerebral artery and posterior cerebral ...
Lesions in the optic tract correspond to visual field loss on the left or right half of the vertical midline, also known as homonymous hemianopsia. A lesion in the left optic tract will cause right-sided homonymous hemianopsia, while a lesion in the right optic tract will cause left-sided homonymous hemianopsia.
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.
Unilateral lesions of the PPRF produce characteristic findings: Loss of horizontal saccades directed towards the side of the lesion, no matter the current position of gaze; Contralateral gaze deviation (acute lesions, such as early stroke, only) Gaze-evoked lateral nystagmus on looking away from the side of the lesion
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.
Middle lesions affecting the uncrossed temporal fibers are rare. These can result in a nasal or binasal hemianopia. Lesions in the body of the chiasm most commonly disrupt the crossing nasal retinal fibers. This leads to a bitemporal hemianopia. The field of vision may still be full when both eyes are open but stereovision will not be possible.
Abnormal blood vessels can form in the back of the eye of a person with diabetes. These new blood vessels are weaker and prone to breaking and causing hemorrhage. [2] Diabetic retinopathy accounts for 31.5–54% of all cases of vitreous hemorrhage in adults in the United States. [1]