**Core Concept**
Accommodation is the process by which the eye changes optical power to maintain a clear image or focus on an object as its distance varies. This is achieved through the shape change of the lens in the eye.

**Why the Correct Answer is Right**
Accommodation occurs due to the contraction of the ciliary muscles, which relaxes the zonular fibers and allows the lens to become more spherical. This increases the refractive power of the lens, enabling the eye to focus on near objects. The maximum accommodation occurs when the ciliary muscles are maximally contracted, allowing the lens to become most spherical.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not specify the mechanism of accommodation.
**Option B:** This option is incorrect as it does not mention the role of the ciliary muscles in accommodation.
**Option C:** This option is incorrect as it does not provide a clear explanation of the accommodation process.

**Clinical Pearl / High-Yield Fact**
The maximum accommodation power of the human eye is achieved when the ciliary muscles are 50-60% contracted, allowing the lens to become 8-10% more spherical.

**Correct Answer: C. Ciliary muscles**