Sense organs (eye and ear)
Iris
Iris
- Origin
- Anterior part of the vascular tunic, suspended between cornea and lens; separates the anterior from the posterior chamber
- Insertion
- Attached to the ciliary body at the iris root; its free inner margin forms the pupillary border
- Function
- Regulates how much light reaches the retina through the sphincter and dilator pupillae muscles (diaphragm of the eye)
- Innervation
- Sphincter pupillae parasympathetic via the oculomotor nerve (III, ciliary ganglion); dilator pupillae sympathetic via the carotid plexus
- Movement & chain
- Miosis on light and convergence, mydriasis in the dark and on sympathetic activation
- Palpation
- Pupillary reaction to light (direct and consensual) and to near vision; a colour difference between the irides is obvious on inspection
- Clinical
- Anisocoria, Horner syndrome (miosis, ptosis, anhidrosis), Adie pupil, anterior uveitis, rubeosis iridis in diabetes
- Segmental innervation
- Parasympathetic III (midbrain, Edinger-Westphal nucleus); sympathetic T1-T2 via the sympathetic chain
- In clinical practice
- Pupil checks belong to every neurological observation: size, symmetry and light response
- Region in the model
- Sense organs (eye and ear)