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Chapter 9. Vision

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A visual exam in an 80-year-old man shows he has loss of vision in the temporal visual field of the left eye and the nasal visual field of the right eye but some vision remains in the central area of the visual field. The diagnosis is

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A. central scotoma.

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B. heteronymous hemianopia with macular sparing.

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C. lesion of the optic chiasm.

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D. homonymous hemianopia with macular sparing.

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E. retinopathy.

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The correct answer is D. Blindness in the left half of both visual fields (temporal field in the left eye and nasal field in the right eye) is classified as a homonymous hemianopia; maintained vision within the central portion of the visual field indicates that there has been macular sparing. All other options can be ruled out for the following reasons. Central scotoma is impaired vision in the center of the visual field. A heteronymous hemianopia is the loss of the temporal visual field in both eyes and is caused by a lesion of the optic chiasm. Retinopathy would cause loss of vision only in the eye with the pathology.

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A visual exam in a 70-year-old woman shows blindness in the temporal visual field of the right eye and the nasal visual field of the left eye. This visual defect could result from a lesion of the

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A. the left optic nerve.

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B. right optic tract.

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C. left lateral geniculate nucleus.

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D. optic chiasm.

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E. right occipital cortex.

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The correct answer is C. The left lateral geniculate nucleus receives information from the nasal field of the left eye and the temporal field of the right eye. All other options can be ruled out for the following reasons. A lesion of the left optic nerve would cause blindness in the left eye. A lesion of the right optic tract would cause blindness in the nasal field of the right eye and the temporal field of the left eye. A lesion of the optic chiasm causes blindness in the nasal field of both eyes. A lesion of the right occipital cortex is likely to cause visual defects in portions of the nasal field of the right eye and portions of the temporal field of the left eye with maintained vision in the central visual field because of the fibers from the foveal (central) region are spread over a large region of the primary sensory cortex.

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