The Distometer (or Vertex Distance) gauge is designed to accurately measure the vertex distance between the apex of the cornea and real surface of the trial lens or the inside surface of the spectacle Rx lens. A change in vertex distance results in a change in the effective power of the lens. This becomes especially sensitive above plus or minus five diopters. A conversion scale is supplied with each distometer instrument, which allows you to quickly and accurately calculate the new correction necessary in the spectacle lens, to obtain the same visual acuity as was achieved with the trial lens.
Patients have been demanding greater Rx accuracy due in part to the increasing popularity of custom progressive addition lenses, many of which require a vertex distance for accurate prescription calculation. This is especially true for the higher power lenses required by Low Vision patients. Further, the increasing use of Prisms for Orthoptic exercises or Vision Therapy require accurate assessment of the vertex distance.
The Metal Distometer and Vextexometer conversion dial are designed for durability and years of reliable use.