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  This Lightweight Plastic Distometer is offered for lighter duty compared to Richmond's Metal Distometer. Includes Plastic Lightweight Distometer (aka Vertexometer), Conversion Dial and instructions. Many practitioners see the vertex distance as increasingly important when correction is greater than 4.00 diopters.
  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. The Conversion Disc is then used to convert the vertex distance into an equivalent lens power for the estimated distance from the eye to the final Rx.
  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. Further, the increasing use of prisms for Orthoptic exercises, Vision Therapy, and Low Vision require accurate assessment of the vertex distance. 6755R Measures vertex distance between Cornea and trial lens to compare with lens mounted in patient's frame. Having the patient close the eye and one end of the instrument or caliper resting against the upper eyelid and the other pressing against the back of surface of the spectacle lens. The scale of the gauge automatically compensates for the lid thickness. The conversion scale permits recalculating the effect of any difference in vertex distance between the trial lenses and the resultant spectacle Rx which can produce an error in the effective power of the correction.
  See' 'Product Instructions and Support Material' tag to download Technical Bulletin or Product Instructions.