Which instrument is used to measure the curvature of the central part of the cornea?

The correct answer is a keratometer. This instrument is specifically designed to measure the curvature of the cornea, particularly in its central area. Understanding corneal curvature is essential in fields like optometry and ophthalmology, as it has a significant impact on a person's vision, especially in determining the proper fit for contact lenses or assessing conditions such as astigmatism.

A keratometer works by projecting a series of illuminated rings onto the cornea and measuring the reflection patterns. The device provides precise readings that help practitioners determine the shape and steepness of the cornea, which aids in creating corrective lenses or planning surgical procedures.

Other options listed serve different purposes: an ophthalmoscope is used for examining the interior of the eye, a keratonometer is often confused with a keratometer but is an older term that may not reflect the latest technology, and a lensmeter measures the power of lenses, not corneal curvature.