The Distometer is used to measure the distance between the apex of the cornea to the back surface of the lens.

What is Distometer used for?

The Distometer or Vertex Distance gauge is designed to accurately measure the vertex distance between the apex of the cornea and rear surface of a trial lens, cornea, and or the rear surface of the spectacle Rx lens. Instructions for use with Trial Frame: Normally a trial lens is placed 5mm to 20mm from the cornea.

Why is back vertex distance important?

“For prescriptions greater than a magnitude of 4 D, the accuracy of the vertex distance is extremely important in determining the necessary power because there is a significant difference between a glasses prescription and the equivalent power at the corneal plane or phakic IOL plane,” Dr.