**Core Concept**
The measurement of corneal thickness is crucial in assessing corneal health, particularly in conditions such as keratoconus, glaucoma, and corneal edema. Corneal thickness can be measured using various methods, each with its own advantages and limitations.

**Why the Correct Answer is Right**
Corneal thickness is typically measured using the following methods:
- **Pachymetry**: This is the most common method, which uses ultrasound or optical coherence tomography (OCT) to measure the thickness of the cornea.
- **OCT**: This non-invasive imaging technique uses low-coherence interferometry to measure corneal thickness and provide high-resolution images of the cornea.
- **Ultrasonic Pachymetry**: This method uses high-frequency ultrasound waves to measure corneal thickness.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it is not a method used to measure corneal thickness.
**Option B:** This option is incorrect because it is a technique used to measure the curvature of the cornea, not its thickness.
**Option C:** This option is incorrect because it is a technique used to measure the shape of the cornea, not its thickness.

**Clinical Pearl / High-Yield Fact**
It is essential to note that corneal thickness measurements can be affected by various factors, including corneal edema, keratoconus, and post-laser surgery changes. Therefore, accurate measurements are crucial for diagnosing and managing corneal diseases.

**Correct Answer: D.**