The annulus of Zinn, also known as the annular tendon or common tendinous ring, is a ring of fibrous tissue surrounding the optic nerve

Optic nerve

The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...

 at its entrance at the apex of the orbit

Orbit (anatomy)

In anatomy, the orbit is the cavity or socket of the skull in which the eye and its appendages are situated. "Orbit" can refer to the bony socket, or it can also be used to imply the contents...

. It is the origin for five of the six extraocular muscles

Extraocular muscles

The extraocular muscles are the six muscles that control the movements of the eye . The actions of the extraocular muscles depend on the position of the eye at the time of muscle contraction.-List of muscles:-Importance:...

. (Some sources only include four.)

It can be used to divide the regions of the superior orbital fissure.

The arteries surrounding the optic nerve

Optic nerve

The optic nerve, also called cranial nerve 2, transmits visual information from the retina to the brain. Derived from the embryonic retinal ganglion cell, a diverticulum located in the diencephalon, the optic nerve doesn't regenerate after transection.-Anatomy:The optic nerve is the second of...

 are sometimes called the "circle of Zinn-Haller" ("CZH"). This vascular structure is also sometimes called "circle of Zinn".

Parts

Some sources distinguish between these terms more precisely, with the annulus tendineus communis being the parent structure, divided into two parts:

• 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

Johann Gottfried Zinn

Johann Gottfried Zinn was a German anatomist and botanist member of the Berlin Academy.- Biography :Johann Gottfried Zinn was born in Schwabach....

. It should not be confused with the Zonule of Zinn

Zonule of Zinn

The zonule of Zinn is a ring of fibrous strands connecting the ciliary body with the crystalline lens of the eye....

, though it is named after the same person.