What is the most accurate tool for measuring vertex distance?

The most accurate tool for measuring vertex distance is the distometer. This instrument is specifically designed to measure the distance from the back surface of the lens to the front surface of the eye or the cornea, which is essential for proper lens fitting and for ensuring the best optical performance of the eyewear.

In contrast, a lens clock typically measures the curvature of the lens surfaces but does not provide a direct measurement of vertex distance. A vertometer, while useful for measuring the power and alignment of the lenses, is not specifically designed for vertex distance measurement. The box-o-graph is mainly used for fitting and measuring frames rather than directly measuring the vertex distance of lenses. Each of these tools serves a different purpose in the process of dispensing ophthalmic lenses, but the distometer is key for accurately determining how far the lens is positioned from the wearer's eye, which can significantly impact vision quality.