What color is the light filter used in applanation tonometry?

In applanation tonometry, a blue light filter is used to help in the accurate measurement of intraocular pressure. The blue filter is essential because it enhances the visibility of the corneal surface during the procedure, allowing for better assessment and precision when the tonometer makes contact with the eye. This visibility is crucial since the primary principle of applanation tonometry is based on the relationship between the pressure inside the eye and the amount of force required to flatten a specific area of the cornea. Without the blue filter, it would be more challenging to achieve the necessary contrast needed to take precise readings.

Other color options may not provide the same level of contrast or visibility that the blue filter offers, making it less effective for this specific application in ocular measurements.