Which term describes the ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening?

Which term describes the ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening?

• A. Iris
• B. Pupil
• C. Retina
• D. Optic Nerve

Answer: (A)

The iris is the ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening. It does this with two layers of smooth muscle: the circular fibers (sphincter pupillae) constrict the pupil in bright light, while the radial fibers (dilator pupillae) widen it in dim light, adjusting how much light enters the eye. The pupil is simply the opening through which light passes; the retina sits at the back of the eye to detect light, and the optic nerve carries visual information from the retina to the brain.

The iris is the ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening. It does this with two layers of smooth muscle: the circular fibers (sphincter pupillae) constrict the pupil in bright light, while the radial fibers (dilator pupillae) widen it in dim light, adjusting how much light enters the eye. The pupil is simply the opening through which light passes; the retina sits at the back of the eye to detect light, and the optic nerve carries visual information from the retina to the brain.