Annulus of Zinn

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). 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. The arteries surrounding the optic nerve are sometimes called the 'circle of Zinn-Haller' ('CZH'). This vascular structure is also sometimes called 'circle of Zinn'.