Illinois Vision Certification Practice Test

What is the primary function of the iris in the eye?

1. To protect the eye from damage

2. To control the amount of light entering the eye

3. To stabilize the eye’s shape

4. To transmit visual signals to the brain

The correct answer is: To control the amount of light entering the eye

The primary function of the iris is to control the amount of light entering the eye. It accomplishes this through the adjustment of its muscles, which can constrict or dilate the pupil – the opening in the center of the iris. When the light levels are high, the iris constricts the pupil to reduce the amount of light that enters, thereby protecting the sensitive retina from excessive brightness and enhancing visual acuity. Conversely, in low-light conditions, the iris dilates the pupil to allow more light to enter and improve visibility. Understanding this function is important for comprehending how the eye adapts to different environmental lighting conditions and plays a critical role in vision. Other options address functions that are not directly related to the iris. For instance, while the eye does have protective mechanisms, such as eyelids and tears, those are not functions of the iris itself. Similarly, stabilization of the eye's shape is primarily the role of the sclera and cornea, not the iris. The transmission of visual signals to the brain involves the retina and the optic nerve, which operate independently of the iris's role in light filtration.