Tonopen

Tonopen is a handheld electronic tonometer used to measure intraocular pressure (IOP). It employs a small, disposable-tipped probe that briefly contacts the cornea; a built-in sensor determines the force required to flatten a portion of the corneal surface, and the device displays the intraocular pressure in millimeters of mercury (mmHg). A topical anesthetic and a sterile disposable cover are typically used to enable contact with the cornea.

Operation involves light, brief contact of the probe with the cornea. The measurement is rapid, usually completed in a few seconds, and several readings are often taken to obtain an average. Tonopen readings can be performed with the patient seated or lying down, and the device is useful when a slit lamp is unavailable or when patient cooperation is limited.

Clinical use and interpretation: Tonopen is widely used in ophthalmology and optometry for glaucoma screening and management, post-surgical care, pediatric examinations, and in field or bedside settings due to its portability. It generally correlates with other tonometers but readings can be influenced by corneal thickness, curvature, or pathology; central corneal thickness can bias results. Clinicians typically take multiple measurements and follow calibration and technique guidelines to improve accuracy.

Safety and maintenance: The device uses disposable tips to reduce infection risk, and the sensor and electronics require periodic calibration according to the manufacturer’s instructions. Tonopen offers a convenient alternative to bench-top applanation tonometry, providing rapid IOP assessment across diverse clinical contexts.