Annulus of Zinn

Annulus of Zinn
Rectus muscles: 2 = superior, 3 = inferior, 4 = medial, 5 = lateral Oblique muscles: 6 = superior, 8 = inferior Other muscle: 9 = levator palpebrae superioris Other structures: 1 = Annulus of Zinn, 7 = Trochlea, 10 = Superior tarsus, 11 = Sclera, 12 = Optic nerve
Anterior view
Details
Identifiers
Latin	Anulus tendineus communis
Dorlands /Elsevier	a_50/12143789
TA	A15.2.07.015
FMA	49071
Anatomical terminology

The annulus of Zinn, also known as the annular tendon or common tendinous ring, is a ring of fibrous tissue surrounding the optic nerve at its entrance at the apex of the orbit. It is the common origin of the four rectus muscles (extraocular muscles).

It can be used to divide the regions of the superior orbital fissure.^[1]

The arteries surrounding the optic nerve are sometimes called the "circle of Zinn-Haller" ("CZH").^[2] This vascular structure is also sometimes called "circle of Zinn".

The following structures pass through the tendinous ring (superior to inferior):

• Superior division of the oculomotor nerve (CNIII)
• Nasociliary nerve (branch of ophthalmic nerve)
• Inferior division of the oculomotor nerve (CNIII)
• Abducens nerve (CNVI)

Parts

Some sources distinguish between these terms more precisely, with the anulus tendineus communis being the parent structure, divided into two parts:^[3]

• a lower, the ligament or tendon of Zinn, which gives origin to the Rectus inferior, part of the Rectus internus, and the lower head of origin of the Rectus lateralis.
• an upper, which gives origin to the Rectus superior, the rest of the Rectus medialis, and the upper head of the Rectus lateralis. This upper band is sometimes termed the superior tendon of Lockwood.

Eponym

It is named for Johann Gottfried Zinn.^[4][5] It should not be confused with the Zonule of Zinn, though it is named after the same person.

References

Anatomy of the globe of the eye
Fibrous tunic (outer)	Sclera Episcleral layer Schlemm's canal Trabecular meshwork Cornea Limbus layers Epithelium Bowman's Stroma Dua's layer Descemet's Endothelium
Uvea/vascular tunic (middle)	Choroid Capillary lamina of choroid Bruch's membrane Sattler's layer Ciliary body Ciliary processes Ciliary muscle Pars plicata Pars plana Iris Stroma Pupil Iris dilator muscle Iris sphincter muscle
Retina (inner)	Layers Inner limiting membrane Nerve fiber layer Ganglion cell layer Inner plexiform layer Inner nuclear layer Outer plexiform layer Outer nuclear layer External limiting membrane Layer of rods and cones Retinal pigment epithelium Cells Photoreceptor cells (Cone cell, Rod cell) → (Horizontal cell) → Bipolar cell → (Amacrine cell) → Retina ganglion cell (Midget cell, Parasol cell, Bistratified cell, Giant retina ganglion cells, Photosensitive ganglion cell) → Diencephalon: P cell, M cell, K cell, Muller glia Other Macula Perifoveal area Parafoveal area Fovea Foveal avascular zone Foveola Optic disc Optic cup Ora serrata
Anatomical regions of the eye	Anterior segment Adnexa Fibrous tunic Anterior chamber Aqueous humour Iris Posterior chamber Ciliary body Lens Capsule of lens Zonule of Zinn Posterior segment Vitreous chamber Vitreous body Retina Choroid
Other	Keratocytes Ocular immune system Tapetum lucidum Eye care professional Eye disease Refractive error Accommodation Physiological Optics Visual perception