Which instrument is designed to measure intraocular pressure?

The instrument designed to measure intraocular pressure is the tonometer. This device plays a crucial role in diagnosing and managing conditions such as glaucoma, where elevated intraocular pressure can lead to optic nerve damage and vision loss. The tonometer measures the pressure inside the eye, which is essential for assessing the eye's overall health.

An ophthalmoscope is used to examine the interior structures of the eye, particularly the retina and optic nerve head, but it does not measure intraocular pressure. A retinoscope is utilized to determine the refractive error of the eye by evaluating the light reflex from the retina, and it also does not provide measurements of intraocular pressure. An autorefractor, on the other hand, automates the process of measuring how the eye focuses light and helps determine the prescription for glasses, but it does not assess intraocular pressure either. Thus, among the listed options, the tonometer definitively fulfills the requirement of measuring intraocular pressure.