Goldmannapplanation

Goldmann applanation tonometry is a method for measuring intraocular pressure (IOP) by determining the force required to flatten a defined area of the cornea. It is widely used in ophthalmology and is often regarded as the reference standard for IOP assessment when performed with a slit-lamp biomicroscope.

The technique relies on applanation tonometry, based on a practical adaptation of the Imbert-Fick principle for the eye. The Goldmann instrument uses a flat prism that contacts the cornea after topical anesthesia and fluorescein dye. The examiner adjusts the position until a predefined corneal area—approximately 3.06 millimeters in diameter—is flattened. The force needed to achieve this applanation is translated into an IOP value and read in millimeters of mercury (mmHg).

During the procedure, the patient is seated at a slit lamp. A topical anesthetic and fluorescein are applied, and the prism gently contacts the cornea. The tear film forms a meniscus around the flattened area; when the inner edges of the fluorescein pool align, applanation is achieved and the reading is obtained. To improve accuracy, multiple readings are often taken and averaged.

Readings are influenced by corneal properties, including central thickness, curvature, and rigidity, as well as tear film quality. Thicker corneas tend to yield higher readings, while thinner corneas yield lower ones; edema, scarring, contact lens wear, and other corneal pathologies can also affect results. Proper technique and regular calibration enhance reliability.

Developed by Hans Goldmann in the 1950s, Goldmann applanation tonometry remains the standard reference method for IOP measurement in many clinics, typically mounted on a slit lamp and requiring anesthesia and a disposable prism or sterilizable head. Safety considerations include minor corneal abrasion and infection risk, mitigated by sterile technique.