Which tool is specifically used to measure vertex distance?

The disometer is the correct tool used to measure vertex distance. Vertex distance refers to the space between the back surface of a spectacle lens and the front of the eye, which can significantly affect the visual performance of the eyewear, especially in high prescription lenses. The disometer is specifically designed to accurately measure these distances, ensuring that lenses are positioned correctly in relation to the user's eyes for optimal vision correction.

The lensometer is used for measuring the prescription of finished lenses and does not focus on vertex distance. A caliper is a general measuring tool that can measure various dimensions but lacks the specificity and accuracy required for vertex distance measurements. The radiuscope is utilized to measure the curvature of lens surfaces, making it inappropriate for vertex distance measurement. Each of these tools has its own distinct functions in optics, but the disometer is uniquely suited to assess the vertex distance with precision.