Kaplan Nursing Entrance Practice Exam

What effect does the iris have on vision?

1. Adjusts the cornea's curvature

2. Controls the size of the pupil

3. Regulates breathing

4. Powers reflex actions

The correct answer is: Controls the size of the pupil

The iris plays a crucial role in vision by controlling the size of the pupil, which directly influences the amount of light that enters the eye. By adjusting the diameter of the pupil, the iris helps to optimize vision under varying lighting conditions. In bright light, the iris constricts the pupil to reduce the amount of light entering, protecting the retina from damage and enhancing visual acuity. In low light, the iris dilates the pupil to allow more light to enter, enabling better night vision. The other options relate to functions that the iris does not perform. While the curvature of the cornea is important for focusing light onto the retina, that adjustment is managed by the cornea itself and the lens of the eye, not the iris. Breathing regulation is primarily controlled by the respiratory system and the brain. Reflex actions involve various neural pathways and are not powered by the iris. Thus, the ability of the iris to control pupil size is the correct and significant aspect relevant to vision.