The submacular choroidal vascular pattern was investigated by experimental occlusion of either one of the temporal short posterior ciliary arteries (SPCAs) or 1, 2, 3 or all of the vortex veins in 87 rhesus monkey eyes and evaluation of their filling defects and anastomoses by fluorescein fundus angiography (FFA). No special artery supplying the submacular choroid was seen. All the temporal SPCAs entered the eyeball in the macular region and each artery supplied a segment of the choroid, with no anastomoses between the adjacent segments. Most of the segments of the choroid supplied by the temporal SPCAs and their watershed zones met in the macular region. Similarly the four quadrants of the uveal tract drained by the four vortex veins and their watershed zones met in the macular region. Since an area where numerous watershed zones meet is most vulnerable to ischaemic disorders, the macular region is likely to show special vulnerability to any generalized chronic ischaemic disorder of the choroid. This, however, would not hold good in occlusion of a single SPCA, because the latter supplies only a small segment of the macular region. It is postulated that senile macular degeneration, senile disciform macular degeneration and allied macular disorders are most probably due to this unusual pattern of the submacular choroid and its special vulnerability to suffer in generalized chronic choroidal ischaemia as compared to the rest of the choroid.