**Core Concept**
The lens derives its nutrition from the aqueous humor, which is a clear fluid produced by the ciliary body and flows through the pupil into the anterior chamber of the eye. This fluid provides essential nutrients and oxygen to the lens, allowing it to maintain its transparency and function.

**Why the Correct Answer is Right**
The lens is avascular, meaning it lacks blood vessels, and relies on the aqueous humor for its nutritional needs. The aqueous humor is secreted by the ciliary body and flows through the pupil into the anterior chamber, where it bathes the lens and cornea. The lens is able to absorb oxygen and nutrients from the aqueous humor, which is rich in glucose, amino acids, and other essential nutrients.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because the lens does not receive its nutrition from the vitreous humor, which is a gel-like substance that fills the posterior chamber of the eye.

**Option B:** This option is incorrect because the lens does not receive its nutrition from the blood vessels in the iris, which are not in direct contact with the lens.

**Option C:** This option is incorrect because the lens does not receive its nutrition from the optic nerve, which is a bundle of nerve fibers that transmits visual information from the eye to the brain.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the lens is avascular, and its nutritional needs are met by the aqueous humor. This is why lens injuries or conditions can lead to cataracts, which are characterized by the clouding of the lens due to a lack of nutrients and oxygen.

**Correct Answer: C. Vitreous humor.**