**Core Concept**
Shirmer's test is a diagnostic tool used to assess the function of the lacrimal gland and the integrity of the tear ducts. It evaluates the ability of the eye to produce tears in response to irritation, providing valuable information about the ocular surface and potential tear disorders.

**Why the Correct Answer is Right**
Shirmer's test involves placing a small strip of filter paper in the lower eyelid to measure the amount of tears produced over a set period. The test is based on the principle that a healthy lacrimal gland produces a sufficient amount of tears to keep the eye moist and comfortable. The normal response is an increase in tear production in response to irritation, indicating a functioning lacrimal gland and tear ducts.

**Why Each Wrong Option is Incorrect**
* **Option A:** Shirmer's test is not primarily used to diagnose conjunctivitis, as it assesses tear production rather than inflammation.
* **Option B:** Shirmer's test is not a measure of corneal sensitivity, but rather a test of tear production and lacrimal gland function.
* **Option C:** Shirmer's test is not a diagnostic tool for glaucoma, as it does not measure intraocular pressure or assess the optic nerve.

**Clinical Pearl / High-Yield Fact**
A normal Shirmer's test result is essential for diagnosing dry eye syndrome, a common condition characterized by reduced tear production and ocular discomfort.

**Correct Answer:** D. To assess tear production and lacrimal gland function.