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The circle of Zinn is an arterial anastomotic ring surrounding the optic nerve head in the sclera formed by branches of the short posterior ciliary arteries. Multiple small branches from the circle of Zinn supply the anterior pia of the optic nerve, the optic disc and contribute to the blood supply of the posterior choroid.[1]

Schematic diagram: Blood Supply of the Border Tissue. Short posterior ciliary arteries form the circle of Zinn-Haller which supply the LC and border tissue of Elschnig. The central retinal artery is destined for the retina and does not contribute to the border tissue.[9]

What is the Circle of Zinn Haller?

The circle of Haller and Zinn comprises complete or incomplete anastomoses around the optic nerve between the medial and lateral short posterior ciliary arteries (SPCAs), which form a dense capillary plexus around the optic nerve.[2]

What is the function of the Circle of Zinn?

The para-optic branches have divided on each side to form the 'circle' of Haller and Zinn which provides pial branches to the retrolaminar optic nerve and recurrent choroidal branches to the peri-papillary choroid and peripheral vertical meridional choroid.[3]

What is The Circle of Zinn and Haller?

The circle of Zinn–Haller (CZH) is known to be an intrascleral arteriolar anastomosis derived from medial and lateral paraoptic short posterior ciliary arteries (SPCAs). The significance of this arterial circle in supplying the anterior optic nerve and peripapillary region has been the subject of controversy.[4] eResearch by Navid Ajamin -- autumn 2024

What is the circle of Zinn formed by?

The peripapillary arterial circle of Zinn-Haller (ZHAC) is an intrascleral arterial anastomosis derived from the paraoptic medial and lateral short posterior ciliary arteries. Arterial circle of Zinn-Haller provides the main vascular supply for the optic nerve head at the level of the lamina cribrosa.[5]

The ciliary arteries are divisible into three groups, the long posterior, short posterior, and the anterior.

• The short posterior ciliary arteries from six to twelve in number, arise from the ophthalmic artery as it crosses the optic nerve.
• The long posterior ciliary arteries, two for each eye, pierce the posterior part of the sclera at some little distance from the optic nerve.
• The anterior ciliary arteries are derived from the muscular branches of the ophthalmic artery. [7]

Short posterior ciliary arteries

The short posterior ciliary arteries are a number of branches of the ophthalmic artery. They pass forward with the optic nerve to reach the eyeball, piercing the sclera around the entry of the optic nerve into the eyeball.

The number of short posterior ciliary arteries varies between individuals; one or more short posterior ciliary arteries initially branch off the ophthalmic artery, subsequently dividing to form up to 20 short posterior ciliary arteries.

The short posterior ciliary arteries branch off the ophthalmic artery as it crosses the optic nerve medially.

About 7 short posterior ciliary arteries accompany the optic nerve, passing anterior-ward to reach the posterior part of the eyeball, where they divide into 15-20 branches and pierce the sclera around the entrance of the optic nerve.

The short posterior ciliary arteries contribute arterial supply to the choroid, ciliary processes, optic disc, the outer retina, and Bruch's membrane.

Some branches of the short posterior ciliary arteries supply the optic disc by means of an anastomotic ring - the circle of Zinn-Haller or circle of Zinn - which is associated with the fibrous extension of the ocular tendons (common tendinous ring (also annulus of Zinn)).[6]

The peripapillary artery, also known as the circle of Haller and Zinn, is the vessel that provides most of the blood supply to the lamina cribrosa (LC) region of the optic nerve.[8]

Reference:

1. radiopaedia.org/articles/circle-of-zinn
2. pmc.ncbi.nlm.nih.gov/articles/PMC3308474
3. nature.com/articles/eye199038.pdf
4. bjo.bmj.com/content/83/7/862
5. journals.lww.com/retinajournal/abstract/2017/02000/peripapillary_arterial_ring_of_zinn_haller_in.10.aspx
6. en.wikipedia.org/wiki/Short_posterior_ciliary_arteries
7. en.wikipedia.org/wiki/Ciliary_arteries
8. pmc.ncbi.nlm.nih.gov/articles/PMC3308474
9. researchgate.net/figure/Schematic-diagram-Blood-Supply-of-the-Border-Tissue-Short-posterior-ciliary-arteries_fig5_338955428
10. link.springer.com/chapter/10.1007/978-1-4419-6724-4_7

See also:

• Circle of Zinn vs annulus of Zinn