**Core Concept**
The normal pH of tears is an essential aspect of ophthalmology and optometry, as it helps maintain the health of the ocular surface. The pH of tears is critical in preventing irritation and inflammation of the eyes. A narrow pH range is necessary for the proper functioning of the ocular surface and the health of the cornea.

**Why the Correct Answer is Right**
The pH of tears is tightly regulated by the lacrimal gland and the accessory lacrimal glands. The normal pH of tears is slightly alkaline, ranging from 6.5 to 7.5. This alkaline environment helps to neutralize acidic substances that may come into contact with the eyes, such as acidic pollutants or bacteria. The pH of tears is also essential for the proper functioning of the corneal epithelium, which is the outermost layer of the cornea. A pH outside the normal range can lead to corneal irritation, inflammation, and even ulcers.

**Why Each Wrong Option is Incorrect**
**Option A:** A pH of 5.5 is too acidic, which can lead to corneal irritation and inflammation. It is not within the normal range for tears.
**Option B:** A pH of 8.5 is too alkaline, which can also lead to corneal irritation and inflammation. It is not within the normal range for tears.
**Option C:** A pH of 7.0 is within the normal range, but it is not the most accurate answer. The normal pH of tears is slightly alkaline, ranging from 6.5 to 7.5.

**Clinical Pearl / High-Yield Fact**
The pH of tears is a critical factor in maintaining the health of the ocular surface. A pH outside the normal range can lead to corneal irritation, inflammation, and even ulcers.

**Correct Answer:** C. 7.0