Visual Pathway Lesions

Bitemporal hemianopia: This is a bitemporal hemianopia, a defect associated with chiasmal lesions. Note that the defects in the two eyes involve only the temporal fields and that their borders are aligned to the vertical meridian passing through fixation. The temporal fields are lost because the ganglion cell axons that originate in the nasal retina and cross in the optic chiasm are selectively vulnerable to compression by mass lesions in this neighborhood: pituitary tumor, craniopharnygioma, astrocytoma, sphenoid meningioma, and carotid artery aneurysm.

Incongruous homonymous hemianopia: You are looking at an incongruous homonymous hemianopia, a defect pattern associated with an optic tract lesion. As with any lesion affecting the visual pathway behind the optic chiasm, there is a temporal hemianopic defect in the field of the contralateral eye and a nasal hemianopic defect in the field of the ipsilateral eye. The combination of these defects is call a "homonymous hemianopia." If the retrochiasmal lesion does not destroy all the visual pathway axons, the homonymous hemianopia will be incomplete, as it is here. Incomplete homonymous hemianopias tend to be dissimilar in extent in the two eyes ("incongruous") when lesions are in the optic tract, but relatively similar in extent in the two eyes ("congruous") when lesions are in the lateral geniculate body, optic radiations, or visual cortex.

Congruous homonymous hemianopia: You are looking at a congruous homonymous hemianopia, a defect pattern associated with an optic radiation or visual cortex lesion. As with any lesion affecting the visual pathway behind the optic chiasm, there is a temporal hemianopic defect in the field of the contralateral eye and a nasal hemianopic defect in the field of the ipsilateral eye. The combination of these defects is called a "homonymous hemianopia." If the retrochiasmal lesion does not destroy all the visual pathway, the homonymous hemianopia will be incomplete, as it is here. Unlike incomplete homonymous hemianopic defects associated with optic tract lesions, those associated with lesions of the optic radiations and visual cortex are similar in extent, or "congruous."

Central scotoma: The visual field defect in the left eye is a central scotoma. It is generated by an optic nerve or foveal lesion. (The visual field of the right eye is normal.) The data are obtained from static perimetry. In the lower plot, the black squares indicate points in the field where the patient could only see very bright targets. The collection of these black squares makes up a visual field defect. In the upper plot, the area between the test points is interpolated to generate a gray scale; it allows you to appreciate the shape of the field defect more easily. Common causes of this defect shape are inflammatory, compressive, toxic, hereditary, nutritional, and mitochondrial disorders.

Cecocentral scotoma: The visual field defect in the left eye is a cecocentral scotoma. It is generated by an optic nerve lesion. (The visual field of the right eye is normal.) The defect extends from fixation toward the physiologic blind spot (the "ceco" means "blind" in Greek). Common causes of this defect pattern are toxic, hereditary, and nutritional optic nerve disorders.

Arcuate scotoma: The visual field defect in the left eye is an arcuate scotoma. It is generated by an optic nerve lesion. (The visual field of the right eye is normal.) Note that the defect fans out from the physiologic blind spot into the nasal field and abuts on the hortizontal meridian. Common causes of this defect pattern are glaucoma, ischemic optic neuropathy, and compression of the optic nerve by tumor.

Temporal wedge scotoma: The visual field defect in the left eye is a temporal wedge scotoma. It is a relatively rare defect generated by an optic nerve lesion. (The visual field of the right eye is normal.) The defect fans out radially from the physiologic spot into the temporal field. Common causes are congenital optic nerve dysplasia and glaucoma.