**Core Concept**
The intraocular pressure (IOP) in a normal population is a critical factor in maintaining the health of the eye. A normal IOP is essential to prevent conditions such as glaucoma, which can lead to vision loss. The average IOP in a normal population is typically between 10-21 mmHg.

**Why the Correct Answer is Right**
The correct answer is within the range of 10-21 mmHg, as this range is considered normal for the general population. This range is determined by the Goldman applanation tonometer, which is a commonly used device for measuring IOP. The Schiotz tonometer, another device used to measure IOP, also supports this range. A normal IOP is crucial for maintaining the health of the optic nerve and preventing damage.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because IOP values below 10 mmHg may indicate ocular hypotension, which can lead to vision problems.
* **Option B:** This option is incorrect because IOP values above 21 mmHg may indicate ocular hypertension, which can increase the risk of glaucoma.
* **Option C:** This option is incorrect because IOP values in children and young adults may be lower than those in the general population.

**Clinical Pearl / High-Yield Fact**
A normal IOP is essential for maintaining the health of the optic nerve, and values outside the normal range can lead to vision problems.

**Correct Answer: C. 11-21 mmHg**