ABO Ophthalmology Complete Practice Exam 2025

The lens of the eye is a transparent structure located behind the iris and the pupil, and it plays a critical role in vision by focusing light onto the retina. The ability of the lens to change shape—becoming thicker or thinner—is essential for accommodation, which is the process that allows us to focus on objects at varying distances. When we look at something close, the ciliary muscles contract, causing the lens to become more rounded. Conversely, when we focus on distant objects, the ciliary muscles relax, and the lens flattens. This dynamic adjustment is key to maintaining clear vision across a range of distances.

In contrast, other structures, such as the cornea, also contribute to light refraction but do not change shape significantly to focus light. The iris controls the amount of light entering the eye by adjusting the size of the pupil and does not alter shape for focusing. The sclera, the tough outer layer of the eye, provides structural support and does not play a role in focusing light at all. Understanding these functions clarifies why the lens is specifically responsible for changing shape to focus light.