Opticians Handbook

An original device for measuring vertex distance is called a Distometer. While unavailable for awhile, it's been remanufactured and sold through Western Ophthalmics (click on the image for the link...

 When wearing glasses, the distance from the front of the cornea to the back surface of a lens is called the Vertex Distance. Why is this measurement important?

This method sometimes works if the pupillometer can get close enough to the eye so the image is not too blurred. To help, pull back the forehead bar.

Set the distance dial to infinity. Move the thumb slides to the temporal most direction, look at the value in mm (will be about 38.5mm).