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Recurrent and collateral branches of circle of Zinn

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Here is a comprehensive account of the recurrent and collateral branches of the circle of Zinn (circle of Haller and Zinn / Zinn-Haller arterial circle):

Circle of Zinn-Haller — Overview

The circle of Zinn-Haller (CZ) is an incomplete, intrascleral arterial ring encircling the optic nerve head (ONH) at the level of the peripapillary sclera/choroid. It is formed primarily by 4–8 short posterior ciliary arteries (SPCAs), specifically the paraoptic SPCAs, and is often partial or substituted by small branches of the paraoptic SPCAs directly from the sclera.

Recurrent Branches of the Circle of Zinn

The circle gives off several recurrent branches — vessels that run posteriorly (away from the globe) after arising from the circle:

1. Recurrent Pial Branches (most important)

  • Arise from the circle of Zinn-Haller and run posteriorly along the optic nerve within the pia mater
  • Join the pial vascular plexus on the retrolaminar optic nerve
  • They anastomose with pial branches of the central retinal artery (CRA) (arising from the CRA's intravaginal segment) anteriorly, and with collateral branches of the ophthalmic artery posteriorly
  • These anastomoses are typically largest on the inferior aspect of the optic nerve
  • This recurrent pial network forms an extensive plexus supplying the retrolaminar optic nerve centripetally

2. Recurrent Choroidal Branches

  • Recurrent choroidal arteries arising from the circle run back toward and contribute to the pial network
  • They form part of the complex peripapillary choroidal supply to the prelaminar region of the ONH

Collateral Branches of the Circle of Zinn

These are branches that arise directly from the circle to supply adjacent structures:

1. Direct Branches to Lamina Cribrosa

  • The circle provides centripetal perforating branches directly into the lamina cribrosa — the primary source of blood supply to this region
  • These are short, penetrating arterioles passing inward from the scleral circle

2. Branches to Prelaminar Region

  • Along with the peripapillary choroid, centripetal branches from the CZ contribute to the prelaminar region of the ONH

3. Branches to Peripapillary Choroid

  • The circle gives branches to the prechoriocapillaris peripapillary choroid surrounding the optic disc

4. Collateral Branches of the Ophthalmic Artery (Hayreh's "Col. Br.")

  • The ophthalmic artery itself gives off collateral branches that run along the pial surface of the optic nerve
  • These are situated most commonly on the inferior aspect of the optic nerve
  • They anastomose posteriorly with the pial branches of the CRA and anteriorly with the recurrent pial branches from the CZ
  • In Hayreh's classic work, these collateral branches from the ophthalmic artery were demonstrated to establish variable collateral circulation in central retinal artery occlusion (CRAO)

Summary Table

Branch TypeOriginDirectionSupplies
Recurrent pial branchesCircle of ZinnPosteriorly along optic nerveRetrolaminar pial plexus; anastomose with CRA pial branches
Recurrent choroidal branchesCircle of ZinnPosteriorly / pial networkPial plexus, retrolaminar nerve
Direct laminar branchesCircle of ZinnCentripetally (inward)Lamina cribrosa
Prelaminar branchesCircle of ZinnCentripetallyPrelaminar ONH
Peripapillary choroidal branchesCircle of ZinnChoroidPrechoriocapillaris peripapillary choroid
Collateral branches (OA)Ophthalmic arteryAlong pial surfaceAnastomose with CRA pial branches + CZ recurrent branches

Clinical Significance

  • The recurrent pial branch anastomoses between the CZ and CRA are large enough to establish partial collateral circulation in CRAO, explaining why some visual function may be preserved
  • Because the optic nerve head is an end-arterial system, the circle of Zinn is inconsistent (absent in some eyes), making NAION produce sectoral disc edema — it leaves watershed zones unperfused when ciliary pressure drops
  • A cilioretinal artery may arise from the circle of Zinn-Haller (in addition to choroidal origin), providing macular sparing in CRAO
Sources: Kanski's Clinical Ophthalmology 10th ed.; ScienceDirect – Ophthalmic Artery (Hayreh data); Cureus review McAllister et al.; Entokey – Posterior Ciliary Artery (Hayreh)
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