What is the diameter of the plastic prism within the applanation tonometer?

The diameter of the plastic prism within the applanation tonometer is typically 7mm. This specific size is important for ensuring accurate pressure measurements in the eye. The principle of applanation tonometry relies on flattening a small, known area of the cornea, and the 7mm diameter allows for a proper balance between minimizing the area of corneal contact and obtaining a reliable measurement of intraocular pressure (IOP).

Using a prism of the correct size helps create a consistent applanation level and reduces variability in readings that may occur with different diameters. If the prism were larger or smaller, it could lead to discrepancies in the measurements due to larger or insufficient contact areas affecting the fluid dynamics at the corneal surface.

In the context of this question, understanding the appropriate dimensions of the various components of an applanation tonometer is crucial for accurate intraocular pressure assessment and proper eye care practices.