Collateral and recurrent branches of circle of Zinn
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Circle of Zinn-Haller — Collateral and Recurrent Branches
What is the Circle of Zinn-Haller?
The arterial circle of Zinn-Haller (also called the circle of Haller and Zinn, or vascular circle of the optic nerve) is an incomplete intrascleral arterial ring located in the peripapillary sclera, encircling the optic nerve at the level of the lamina cribrosa/choroid. It is not present in every eye (often incomplete or even absent).
Feeding Vessels (Afferent Supply to the Circle)
The circle receives blood from:
- Short posterior ciliary arteries (SPCAs) — the dominant source (4–8 paraoptic SPCAs contribute directly during their intrascleral course)
- Choroidal vessels — peripapillary choroidal branches
- Pial arterial network — contributions from the pia mater surrounding the optic nerve
(Kanski's Clinical Ophthalmology, 10th ed.; Adams & Victor's Neurology, 12th ed.)
Collateral Branches
Collateral branches arise from the ophthalmic artery itself and run along the pia mater of the optic nerve. They anastomose with:
- Recurrent pial branches of the circle of Zinn-Haller anteriorly
- Pial branches of the central retinal artery (CRA) — arising from its intravaginal segment — to form an anastomotic pial plexus on the optic nerve
These pial anastomoses are most commonly situated on the inferior aspect of the optic nerve. They can establish collateral circulation in the event of CRA occlusion at its site of penetration into the nerve. — Hayreh (via ScienceDirect)
Specific collateral branches described:
| Branch | Origin | Target |
|---|---|---|
| Collateral branches of ophthalmic artery (Col. Br.) | Ophthalmic artery | Pial plexus of retrobulbar optic nerve |
| Pial branches of CRA | CRA (intravaginal part) | Pial plexus; anastomose with recurrent pial branches of CZ |
| Intraseptal vessels | Retrolaminar region | Large precapillaries around axon bundles (lamina cribrosa → intraorbital nerve) |
Recurrent Branches
The circle of Zinn-Haller gives off recurrent branches that run posteriorly to supply:
- Recurrent pial branches → run posteriorly into the pial vascular plexus of the retrolaminar optic nerve, contributing to its centripetal blood supply
- Recurrent choroidal arteries → supply the peripapillary choroid anteriorly (centripetal branches to the prelaminar region)
- Direct branches to the laminar and retrolaminar ONH — though these are infrequent
Zones Supplied (Summary by Region)
| ONH Region | Primary Supply |
|---|---|
| Surface nerve fiber layer | Branches of central retinal artery |
| Prelaminar region | Peripapillary choroid (recurrent choroidal arteries from SPCA system) |
| Lamina cribrosa | Centripetal branches of SPCAs ± circle of Zinn-Haller directly |
| Retrolaminar region | Pial network (recurrent pial branches from CZ + collateral branches of OA); sometimes axial supply from CRA |
Clinical Significance
- Because the optic nerve head is an end-arterial system supplied largely by SPCAs and the circle of Zinn-Haller, sectoral disc edema is the hallmark of non-arteritic anterior ischemic optic neuropathy (NAION) — an infarct in one sector of this end-arterial territory.
- In ~⅓ of individuals, a cilioretinal artery may arise from the circle of Zinn-Haller (or peripapillary choroid) to supply the macula — clinically important in central retinal artery occlusion (CRAO), as the macula may be spared.
- The pial anastomotic network between collateral branches of the ophthalmic artery, recurrent pial branches of CZ, and CRA pial branches provides a route for partial collateral perfusion during CRA occlusion.
(Kanski's 10th ed.; Bradley & Daroff's Neurology; Adams & Victor's 12th ed.; McAllister et al., Cureus 2013)
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