What color is the light filter used in applanation tonometry?

The light filter used in applanation tonometry is blue. In applanation tonometry, a blue light filter is employed to enhance the visibility of the fluorescein dye during the measurement process. The blue filter specifically helps in detecting the fluorescein, allowing for accurate visualization of the tear film and corneal surface, which is critical for obtaining precise intraocular pressure readings.

Using blue light also improves contrast, making it easier for the practitioner to observe the applanation process on the corneal surface. This is important in ensuring that the measurements taken are reliable and consistent, as interference from ambient light can affect the accuracy of the readings if not adequately filtered.