Certified Paraoptometric (CPO) Exam – Practice Test & Study Guide 2025

The cornea is the primary structure responsible for focusing light as it enters the eye. It is a transparent layer that covers the front of the eye and has a curved shape, allowing it to bend (refract) incoming light rays. This refraction is crucial for the formation of a clear image on the retina, which is located at the back of the eye.

While the pupil does control the amount of light that enters the eye, it does not participate in focusing that light. The retina, on the other hand, is the light-sensitive tissue that detects the focused image created by the cornea and the lens, but its role is more about image reception and processing rather than focusing. The sclera is the white outer layer of the eye that provides protection and shape but does not play a role in focusing light. Thus, the cornea's unique properties and position make it essential for the initial refraction of light, enabling clearer vision.