editor: Adler’s physiology of the eye, ed 9, St Louis, 1992, Mosby.)

248 Clinical Anatomy of the Visual System

A B C

FIGURE 13-23

A, CT scan showing pituitary adenoma causing a bitemporal visual field loss. B, CT scan showing aneurysm of left internal carotid artery as it passes through cavernous sinus, resulting in binasal visual field loss, and affecting CN III and CN IV. C, MRI showing lesion of left temporal lobe secondary to CVA resulting in right homonymous superior quadrantanopia. (A-C courtesy Weon Jun, O.D., Portland VA Medical Center, Portland, Ore.)

FIGURE 13-24

Automated visual fields showing right congruent homonymous field loss; absolute defect inferior quadrant, relative defect superior quadrant, caused by arteriovenous malformation (AVM in left occipital cortex). AVM successfully obliterated by embolization, visual field loss remained. (Courtesy Edward B. Mallett, O.D., Tillamooh Optometric Clinic, Tillamook, Ore.)

CHAPTER 13  t  Visual Pathway 249

FIGURE 13-25

Schematic representation of architecture of geniculocalcarine pathway with projection of striate cortex and nerve fiber bundles of optic radiation onto visual field. A, Right homonymous half field divided into sectors and concentric zones representing projection of various bundles of optic radiations in temporal and parietal lobes and in striate cortex in occipital lobe. B, C, and D, Coronal sections (seen from in front) through temporal, parietal, and parietooccipital lobes of left cerebral hemisphere showing planes of section, relationship of optic radiations to lateral ventricle, and division of visual fiber bundles in optic radiations into sectors and concentric zones corresponding to their projection onto visual field. Note in plane of section through temporal loop of Meyer (B) that only lower half of radiations are represented; in planes B and C, that section anterior radiations, macular fibers (1 to 6) are laminated on lateral surface of radiations; and in plane D, that section’s posterior radiations, macular fibers are interposed between and completely separate upper and lower peripheral fibers. E, Medial view of left cerebral hemisphere showing striate cortex divided according to its projection on right homonymous half field. F, View from behind striate cortex at posterior tip of left occipital pole showing projection of macular portion of right homonymous defect. (From Harrington DO, Drake MV: The visual fields; text and atlas of clinical perimetry, ed 6, St Louis, 1990, Mosby.)

250 Clinical Anatomy of the Visual System

FIGURE 13-26

Revised map of the visual field in the human striate cortex. It is important to emphasize that considerable variation occurs among individuals in the exact size and location of striate cortex. This new map provides the best fit for our data. A, View of left occipital lobe with the calcarine fissure opened, exposing the striate cortex. Dashed lines indicate the coordinates of the visual field map. The representation of the horizontal meridian runs approximately along the base of the calcarine fissure. The vertical lines mark the isoeccentricity contours from 2.5 to 40 degrees. The striate cortex wraps around the occipital pole to extend approximately 1cm onto the lateral convexity, where the fovea is represented. B, View of the left occipital lobe, showing the striate cortex, which is mostly hidden within the calcarine fissure (running between arrows). The boundary (dashed line) between the striate cortex (V1) and extrastriate cortex (V2) contains the representation of the vertical meridian, which usually is located along the exposed medial surface of the occipital lobe, as shown, but variation occurs in specimens. C, Projection of the right visual hemifield (D) on the left visual cortex, depicted by transposing the map illustrated in the top left onto a flat surface. The striate cortex is an ellipse measuring approximately 80 × 40 mm, measuring roughly 2500 square millimeters. The row of dots indicates where the striate cortex folds around the occipital pole: the small region between the dots and the foveal representation is situated on the exposed lateral convexity of the occipital lobe. The black oval marks the region of the striate cortex corresponding to the visual field coordinates of the contralateral eye’s blind spot. This region of cortex receives visual input from only the ipislateral eye (HM = horizontal meridian). D, Right visual hemifield shows the V4e isopter plotted with a Goldmann perimeter. The stippled region corresponds to the monocular temporal crescent that is mapped within the most anterior 8 to 10% of the striate cortex (see stippled region of map in C). (Reprinted with permission from Horton JC, Hoyt WF: The representation of the visual field in human striate cortex, Arch Ophthalmol 109:816, 1991)