Optical Segment:
focuses light on the retina using the refractive powers of the cornea and lens
Retinocortical Segment:
transduces light into neural signals that travel through the retina, optic nerve, optic chiasm, optic tracts, lateral geniculate bodies, and optic radiations to primary visual cortex
Perceptual Segment:
the dorsal perceptual stream carries the signal to parietal vision-associated cerebral cortex for visuospatial and attentional vision; the ventral perceptual stream carries the signal to temporal vision-associated cerebral cortex to allow recognition of viewed material
Optical segment:
uncorrected refractive errors and media opacities or irregularities produce unclear vision (but never scotomas!)
Retinocortical segment:
lesions anywhere from the retina to the visual cortex produce visual field defects whose shape often allows localization of the lesion within this segment
Perceptual segment:
lesions of the occipito-parietal stream produce deficits in visuospatial and attentional function; lesions of the occipito-temporal stream produce deficits in visual recognition
