Annulus of Zinn

Orbit – Anterior view – showing Annulus of zinn, intraocular muscles and nerves
Click on Image for an enlarged view
Image by Patrick J. Lynch

• Annulus of zinn is a fibrous ring located in the posterior part of the orbit
• It is located around the optic canal and encloses a part of the superior orbital fissure
• It is the common fibrous origin of the 4 recti muscles
• It is named after Johann Gottfried Zinn

Parts:

• According to some workers, the annulus of zinn has 2 parts:
  • upper part – superior tendon of Lockwood – gives origin to superior rectus, part of medial rectus, and upper head of lateral rectus
  • lower part – ligament / tendon of Zinn – gives origin to inferior rectus, part of medial rectus and lower head of lateral rectus

Structures passing through the ring:

• Through optic canal
  • Optic nerve
  • Ophthalmic artery
• Through superior orbital fissure
  • Superior and inferior divisions of oculomotor nerve
  • Abducens nerve
  • Nasociliary branch of ophthalmic nerve

Structures attached to the ring:

• The 4 recti muscles
• The origins of levator palpebrae superioris and superior oblique are partly attached to the ring even though they lie outside it

Alternate names :

• Annular tendon
• Common tendinous ring
• annulus tendineus communis

Other structures with similar names:

• Zonule of Zinn
• Circle of Zinn