Outer zone of iris
Anulus major iridis
- Latin synonym: Zona ciliaris iridis
- Synonym: Ciliary zone of iris
- Related terms: Outer border of iris
Definition
The outer zone of iris (a.k.a. the greater ring or the ciliary zone of iris) is the peripheral region of the iris extending from the collarette to the ciliary margin of iris.
The outer zone is more irregular and coarser, but also thinner, than the inner zone. It houses the radially arranged muscle fibres of the dilator pupillae muscle, that is responsible for pupil dilatation (mydriasis).
References
Standring, S. (Ed.). (2015). Eye (Chapter 42). In Gray's anatomy: The anatomical basis of clinical practice (41st ed., pp. 686-706). Churchill Livingstone.
