What is the primary use of a tonometer?

The primary use of a tonometer is to measure intraocular pressure, which is crucial in the diagnosis and management of eye conditions such as glaucoma. This device works by applying a small amount of pressure to the eye to determine how much resistance the eye provides. By measuring the pressure inside the eye, healthcare professionals can assess the health of the optic nerve and overall eye health. This measurement is vital since elevated intraocular pressure can lead to damage to the optic nerve and potential vision loss, thus making tonometers an essential tool in ophthalmology.

The other options pertain to entirely different physiological assessments; for instance, assessing joint mobility pertains to musculoskeletal evaluations, monitoring blood sugar levels is related to diabetes management, and evaluating lung capacity involves respiratory assessments. Each of these requires different instruments and methodologies, highlighting the specialized function of the tonometer in eye care.