History And Definitions

The afferent visual pathways encompass structures responsible for perceiving, relaying, and processing visual information: the eyes, optic nerves (cranial nerve II), chiasm, tracts, lateral geniculate nuclei, optic radiations, and striate cortex. In general, the visual abnormalities caused by lesions anterior to and including the chiasm cause acuity (clarity) loss, color deficits, and visual field defects (abnormal central or peripheral vision). From a neuro-ophthalmical standpoint, patients with unilateral retrochiasmal disturbances present primarily with visual field defects without acuity abnormalities. Higher order processing, which is instrumental for interpreting visual images, occurs in extrastriate association cortex. Abnormalities in these areas cause, for instance, deficits in object recognition, color perception, and visual attention (neglect of visual stimuli in left or right hemifields).

This chapter reviews the neuroanatomical features of these structures and provides a systematic approach to the evaluation of clinical syndromes involving cranial nerve II, other parts of the afferent visual pathway, and higher cortical visual areas.

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