A nurse is assessing a patient who reports changes in eye color and discomfort. Understanding that the colored part of the eye plays a critical role in regulating light entry, which anatomical structure is the nurse evaluating?

A. Retina is incorrect because the retina is a thin layer of nerve tissue lining the back of the eye. Its primary function is to detect light and convert it into electrical signals that are transmitted to the brain via the optic nerve. While essential for vision, it does not affect eye color or control light entry. Conditions affecting the retina, such as retinal detachment or diabetic retinopathy, usually present with visual disturbances rather than changes in eye color. B. Sclera is incorrect because the sclera is the tough, white outer layer of the eye that maintains the shape of the eyeball and protects internal structures. Although changes in the sclera (e.g., yellowing in jaundice or redness in conjunctivitis) can indicate systemic or local conditions, it does not influence the amount of light entering the eye or determine eye color. C. Cornea is incorrect because the cornea is the transparent, dome-shaped surface that covers the front of the eye. It plays a critical role in focusing light onto the retina, contributing approximately two-thirds of the eye’s total refractive power. While corneal problems can cause pain, blurred vision, or light sensitivity, the cornea itself is not colored and does not regulate light entry through the pupil. D. Iris is correct because the iris is the pigmented, circular structure surrounding the pupil. The color of the iris gives each individual their eye color. Its muscles—the sphincter and dilator pupillae—control pupil size, regulating the amount of light that enters the eye. In bright light, the sphincter muscles contract to constrict the pupil, reducing light entry and protecting the retina. In dim light, the dilator muscles expand the pupil to allow more light in. Changes in iris color or appearance, combined with discomfort, may indicate inflammation of the iris (iritis), infection, trauma, or other ocular pathologies. Assessing the iris is essential for detecting both structural and functional eye problems.