Iris

Definition

The iris is the colored part of the eye surrounding the pupil that controls the amount of light entering the retina. It adjusts the size of the pupil based on light intensity through muscle contractions.

5 Must Know Facts For Your Next Test

1. The iris contains two sets of smooth muscles: the dilator pupillae and sphincter pupillae.
2. It plays a crucial role in regulating light exposure to photoreceptors in the retina.
3. Eye color is determined by the pigmentation within the iris, primarily melanin.
4. The autonomic nervous system controls its function, with sympathetic nerves causing dilation and parasympathetic nerves causing constriction.
5. Damage or disease affecting the iris can lead to conditions like anisocoria (unequal pupil sizes) or iritis (inflammation).

Review Questions

• What are the two types of muscles found in the iris?
• How does the iris regulate light entering the eye?
• Which part of the nervous system controls pupil dilation and constriction?

Related terms

pupil: The central opening in the iris that allows light to enter the eye.

retina:

The layer at the back of the eyeball containing cells that are sensitive to light.

photoreceptors: Specialized cells in the retina that convert light into electrical signals for vision.