What is the diameter of the contact area of the applanation tonometer?

The diameter of the contact area of the applanation tonometer is specifically set at 3.06 mm. This measurement is critical as it relates to the basic principle of tonometry, which is based on the Imbert-Federmann principle. According to this principle, the pressure inside a sphere (the eye in this case) can be measured by applying a known force over a defined area.

In the case of the applanation tonometer, a fixed diameter of 3.06 mm is used to standardize the measurement of intraocular pressure. This ensures consistent and reliable results across different measurements and patients, as the area of contact directly influences readings of intraocular pressure. Hence, the standardized diameter helps clinicians determine the pressure accurately by providing a uniform surface area for applanation against the cornea.

Knowing this diameter is essential for ocular health assessments and provides the basis for understanding how intraocular pressure readings are influenced by the size of the contact area.