The cortical representation of shadows cast by retinal blood vessels.
OBJECTIVE
We inquired whether the representation of angioscotomas could be detected in the primary (striate) visual cortex.


METHODS
In 12 normal squirrel monkeys, the ocular fundi were photographed and retinal vascular landmarks were projected onto a tangent screen for calibration. Each animal then underwent monocular enucleation under general anesthesia. Animals were perfused after 8 to 10 days, and flat-mounted sections of striate cortex were processed for the metabolic enzyme cytochrome oxidase (CO).


RESULTS
In each animal, the cortical region corresponding to the blind spot appeared as a 3 x 2 mm oval in the CO staining pattern. It stood out because it received input from only 1 eye. In 9 of 12 animals, the representation of the major retinal vessels was also visible, for the same reason. In our best examples, CO sections showed about 10 thin lines radiating from the blind spot representation. Some could be traced for 15 mm, all the way to the vertical meridian. Vessels only 12 minutes of arc in diameter were represented in the cortex. Each angioscotoma representation in the cortex could be matched with its corresponding retinal vessel in the fundus.


CONCLUSIONS
Our findings show that (1) the visual field map in layer IVc is more precise than indicated by physiological studies, and (2) visual experience must refine the final pattern of geniculocortical projections, given that the retinal vessels can produce a shadow only after birth.
Horton
J C
JC
Beckman Vision Center, University of California, San Francisco, School of Medicine, USA.
Adams
D L
DL
D000818:Animals; D003576:Electron Transport Complex IV / Q000378:metabolism; D005654:Fundus Oculi; D009898:Optic Disk / Q000201:enzymology / Q000502:physiology; D012171:Retinal Vessels / Q000033:anatomy & histology / Q000502:physiology*; D012453:Saimiri; D013194:Staining and Labeling; D015349:Vision, Monocular / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*
D003576:Electron Transport Complex IV