**Core Concept**
The corneal curvature is a crucial parameter in ophthalmology, measured to determine the refractive power of the cornea. It is an essential aspect of corneal topography and is used to assess corneal diseases such as keratoconus.

**Why the Correct Answer is Right**
The correct answer is based on the principle that the corneal curvature is measured using a device called an ophthalmometer or a keratometer. These devices utilize the principle of reflection to measure the curvature of the cornea. The keratometer emits a light beam that reflects off the cornea, and the angle of reflection is used to calculate the corneal curvature. This is based on the principles of geometry and optics.

**Why Each Wrong Option is Incorrect**
**Option A:** The autorefractor measures the refractive error of the eye but does not directly measure corneal curvature.
**Option B:** The slit lamp is a diagnostic tool used for anterior segment examination but does not measure corneal curvature.
**Option C:** The ultrasound biomicroscopy (UBM) is a high-frequency ultrasound imaging modality used to visualize the anterior segment but does not measure corneal curvature.

**Clinical Pearl / High-Yield Fact**
A normal corneal curvature is essential for clear vision, and any significant deviation from this can lead to corneal diseases such as keratoconus. It is essential to assess and monitor corneal curvature regularly in patients with corneal diseases.

**Correct Answer: A. Ophthalmometer**