11113 SCAN0149

CHAPTER 11 ▼ Orbital Blood Supply 203

FIGURĘ 11-4

Uveal blood vessels. Blood supply of the eye is derived from ophthalmic artery. Except for central retinal artery, which supplies inner retina, almost the entire blood supply of the eye comes from the uveal vessels. There are two long posterior ciliary arteries; one enters uvea nasally and one enters temporally along horizontal meridian of eye near optic nerve (A). These two arteries give off three to five branches (b) at the ora serrata, which pass directly back to form anterior choriocapillaris. These capillaries nourish retina from eąuator forward. Short posterior ciliary arteries enter choroid around optic nerve (C). They divide rather rapidly to form posterior choriocapillaris, which nourishes retina as far anteriorly as equator (choriocapillaris not shown). This system of capillaries is continuous with those derived from long posterior ciliary arteries. Anterior ciliary arteries (D) pass forward with rectus muscles, then pierce selera to enter ciliary body. Before joining major circle of iris, these arteries give off 8 to 12 branches (e) that pass back through ciliary muscle to join anterior choriocapillaris. Major circle of iris (f) lies in pars plicata and sends branches posteriorly into ciliary body as well as forward into iris (g). Circle of Zinn (h) is formed by piał branches (i) as well as branches from short posterior ciliary arteries. Circle of Zinn lies in selera and furnishes part of blood supply to optic nerve and disc. Vortex veins exit from eye through posterior selera (J) after forming an ampulla (k) near internal selera. Venous branches that join anterior and posterior part of vortex system are meridionally oriented and are fairly straight (I), whereas those joining vortices on medial and lateral sides are oriented circularly about the eye (m). Venous return from iris and ciliary body (n) is mainly posterior into vortex system, but some veins cross anterior selera and limbus (o) to enter episcleral system of veins. (From Hogan MJ, Alvarado JA, Weddell JE: Histology of the human eye, Philadelphia, 1971, Saunders.)

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