Iris
Sensory (eye & ear)OrgansHeadLeft and right
View left in 3D View right in 3D
- What it is
- The coloured, contractile diaphragm in front of the lens, part of the uveal tract. Its front surface shows radial fibres, pit-like crypts and a zig-zag collarette; its back is lined by dark pigment epithelium.
- Function
- Controls how much light enters the eye: the sphincter pupillae (parasympathetic) narrows the pupil, the dilator pupillae (sympathetic) widens it.
- Size
- 12 mm in diameter, 0.3-0.6 mm thick; pupil 2-8 mm.
- Clinical note
- Eye colour depends only on the amount of melanin in the front layers - blue irises have little, brown have much; the crypt pattern is unique enough for biometric iris scans.