Three-dimensional representation of the multilevel collateral circulation in the primate anterior uvea in both surface and cutaway views. To the left, in cross section, perforating branches of the anterior ciliary artery are shown as they pass through the sclera to supply the intramuscular circle and major arterial circle. ACA = anterior ciliary artery; EC = episcleral circle; IMC = intramuscular circle; LPCA = long posterior ciliary artery; MAC = major arterial circle; PACA = posterior perforating anterior ciliary artery; RCA = recurrent ciliary artery.