**Core Concept**
The thickness of the cornea is a crucial parameter in ophthalmology, as it affects the refractive power of the eye and can be involved in various ocular diseases. Measuring corneal thickness is essential for diagnosing and managing conditions such as glaucoma, keratoconus, and corneal edema.

**Why the Correct Answer is Right**
A pachymeter is a specialized device used to measure the thickness of the cornea, typically in micrometers. It works by emitting a low-energy ultrasound wave that penetrates the cornea and is reflected back, allowing the device to calculate the corneal thickness. This measurement is essential for ophthalmic surgeries, such as LASIK, and for monitoring corneal health in patients with glaucoma or other ocular conditions.

**Why Each Wrong Option is Incorrect**
**Option A:** The Schiotz tonometer is used to measure intraocular pressure (IOP) by indenting the cornea with a known weight, which causes a change in the corneal curvature. While it provides valuable information about IOP, it does not measure corneal thickness.

**Option B:** A keratometer is an instrument used to measure the curvature of the cornea, which is essential for calculating the power of the cornea. However, it does not measure the thickness of the cornea.

**Option D:** An aesthesiometer is a device used to assess the sensitivity of the cornea by applying a gentle touch or a small amount of air to the cornea. It is not designed to measure corneal thickness.

**Clinical Pearl / High-Yield Fact**
When performing a comprehensive ophthalmic examination, it's essential to measure corneal thickness using a pachymeter, especially in patients with a history of glaucoma or other ocular conditions that may affect corneal health.

**✓ Correct Answer: C. Pachymeter**