**Core Concept**
The grittiness in the eyes is a symptom of a condition known as conjunctivitis, an inflammation of the conjunctiva, a thin membrane covering the white part of the eye and the inside of the eyelids. This condition can be caused by various factors, including bacterial, viral, or allergic reactions.

**Why the Correct Answer is Right**
The correct answer is related to the presence of a foreign body or an allergen that causes irritation to the conjunctiva. In this case, the grittiness in the eyes suggests the presence of a foreign body or an allergen that has caused the conjunctiva to become inflamed. The everted eyelid will show the foreign body or allergen that is causing the irritation.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not directly relate to the presence of a foreign body or allergen that causes irritation to the conjunctiva.
* **Option B:** This option is incorrect because it is a condition that affects the cornea, not the conjunctiva.
* **Option C:** This option is incorrect because it is a condition that affects the eyelid margin, not the conjunctiva.

**Clinical Pearl / High-Yield Fact**
When examining a patient with conjunctivitis, it is essential to evert the eyelid to search for a foreign body or allergen that may be causing the irritation. This can be done by gently grasping the eyelid with a cotton swab and pulling it outward.

**Correct Answer: D. A small piece of dirt or a foreign body.**