Certified Paraoptometric (CPO) Practice Exam 2026 – All-in-One Study Guide to Ensure Exam Success!

The opening to the inner eye is known as the pupil. The pupil is the circular hole located in the center of the iris, which is the colored part of the eye. Its primary function is to regulate the amount of light that enters the eye by adjusting its size: it dilates to allow more light in when the surrounding environment is dark and constricts in bright conditions to reduce light exposure. This adaptability is crucial for optimal vision under varying lighting conditions.

The other options refer to different parts of the eye: the iris is responsible for controlling the size of the pupil, the cornea is the transparent layer that covers the front of the eye and helps focus light, and the lens is responsible for further focusing light onto the retina. Each of these components plays vital roles, but when it comes to the opening that allows light to enter the inner eye, the pupil is the correct term.