**Core Concept**
Corneal curvature refers to the shape of the cornea, which is a critical factor in determining the eye's refractive power and visual acuity. Corneal curvature is measured in terms of its radius of curvature, which can be calculated using the keratometry (K) readings obtained from a keratometer.

**Why the Correct Answer is Right**
The keratometer is a diagnostic instrument used to measure the corneal curvature by projecting a mire (a series of concentric rings) onto the cornea and then measuring the deviation of the reflected image. The keratometer calculates the corneal curvature based on the principle of refraction and the geometry of the cornea. The resulting keratometry readings are expressed in diopters (D) and are used to determine the power of the cornea.

**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect as it does not accurately describe a method for measuring corneal curvature.
**Option B:** This option is incorrect as it is not a specific instrument used to measure corneal curvature, although it is related to the field of ophthalmology.
**Option C:** This option is incorrect as it is a different method for measuring corneal thickness, not curvature.

**Clinical Pearl / High-Yield Fact**
High myopia is often associated with steep corneal curvature, which can lead to increased risk of retinal detachment and other vision-threatening complications. Therefore, accurate measurement of corneal curvature is crucial in the diagnosis and management of myopia.

**Correct Answer: D. Keratometer**