The Pupil Reflex
- The iris controls the size of the pupil and therefore only lets a certain amount of light to enter the eye
- The iris contains two sets of smooth muscles- circular muscles and radial muscles.
- The circular muscles are arranged in concentric rings around the pupil, while the radial muscles run radially.
- These muscles are antagonistic
- The pupil reflex is the reflex contraction and relaxation of the antagonistic muscles of the iris in response to changes in light intensity. It causes a change in the pupil size.
- The pupil dilates at low light intensities, and constricts at high light intensities
- This allows sufficient light to enter the eye for vision in dim light, while screening off excess light at high light intensities to prevent damage to the retina
- The pupil in the human eye remains circular when contracted or dilated