Which drug is used for applanation tonometry?

Proparacaine is the correct choice for use in applanation tonometry because it is a local anesthetic that numbs the surface of the eye, making the procedure comfortable for the patient. Applanation tonometry is a technique used to measure intraocular pressure, and to perform this procedure, the cornea must be anesthetized to prevent discomfort and reflex tearing during the measurement process. Proparacaine effectively decreases sensitivity in the eye without affecting intraocular pressure readings, allowing for accurate measurement while ensuring patient comfort.

The other drugs listed serve different purposes in ophthalmic practice. Tropicamide is primarily used as a cycloplegic agent to dilate the pupil for examinations but does not provide anesthesia. Phenylephrine is also used to dilate the pupil and does not have anesthetic properties. Timolol is a beta-blocker used to lower intraocular pressure in conditions like glaucoma, but it is not an anesthetic and is not suitable for use in procedures involving direct measurement of intraocular pressure.