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INTRODUCTION

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The retinas and anterior visual pathways (optic nerves, optic chiasm, and optic tracts) (Figures 14–1 and 14–2) are an integral part of the brain, providing a substantial proportion of its total sensory input. The pattern of visual field loss indicates the site of damage in the visual pathway (Figures 14–3 to 14–5). Eye movement disorders may be due to disease of cranial nerves III, IV, or VI, or a more central lesion. Cranial nerves V and VII are also intimately associated with ocular function.

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Figure 14–1.

Magnetic resonance imaging of normal brain in sagittal section (upper left), coronal section (upper right), and axial section (lower left). The white arrows indicate the chiasm.

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Figure 14–2.

The optic pathway. The dotted lines represent nerve fibers that carry visual and pupillary afferent impulses from the left half of the visual field.

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Figure 14–3.

Visual field defects due to various lesions of the optic pathways.

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Figure 14–4.

Occipital lobe abscess. Top: Automated perimetry and tangent screen examination showing homonymous, congruous, paracentral scotoma in right upper visual fields. Bottom: Parasagittal magnetic resonance imaging showing lesion involving left inferior calcarine cortex. (Reproduced, with permission, from Horton JC, Hoyt WF: The representation of the visual field in human striate cortex. A revision of the classic Holmes map. Arch Ophthalmol 1991;109:816. Copyright © 1991. American Medical Association. All rights reserved.)

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Figure 14–5.

Bilateral occipital infarcts with bilateral macular sparing. Top: Tangent screen and superimposed Goldmann visual fields of both eyes showing bilateral homonymous hemianopia with macular sparing, greater in the right hemi-field. Bottom: Axial magnetic resonance imaging showing sparing of occipital poles. (Reproduced, with permission, from Horton JC, Hoyt WF: The representation of the visual field in human striate cortex. A revision of the classic Holmes map. Arch Ophthalmol 1991;109:816. Copyright © 1991. American Medical Association. All rights reserved.)

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THE OPTIC NERVE

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A wide variety of diseases affect the optic nerve (Table 14–1). Clinical features indicative of optic nerve disease are reduction of visual acuity and field, afferent pupillary defect, poor color vision, and optic disk changes.

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Table 14–1.Etiologic Classification of Diseases of the Optic Nerve

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