Certified Paraoptometric (CPO) Practice Exam 2025

Which muscle controls the focusing ability of the eye directly?

1. Retinal muscle

2. Ciliary muscle

3. Rectus muscle

4. Oblique muscle

The correct answer is: Ciliary muscle

The ciliary muscle plays a crucial role in controlling the focusing ability of the eye. It is a smooth muscle located in the eye's middle layer, specifically in the ciliary body, which is adjacent to the lens. When the ciliary muscle contracts, it allows the lens to become thicker, increasing its power to focus on near objects, a process known as accommodation. Conversely, when it relaxes, the lens flattens for distance vision. This muscle directly influences how well we can focus on objects at varying distances, making it essential for clear vision. Other muscles mentioned, such as the retinal muscles, rectus muscles, and oblique muscles, primarily contribute to the eye's movement and positioning rather than the focusing process itself. The retinal muscles are involved in processes related to light detection, while the rectus and oblique muscles control the movement of the eyeball rather than the adjustment of focus.