What is the purpose of a lensmeter?

The purpose of a lensmeter is to measure the prescription of lenses. This instrument is essential in optical practices as it provides a way to accurately assess the power and characteristics of various lenses, including single vision, bifocal, and even progressive lenses. By measuring the diopter value, axis, and other refractive properties, optical professionals can ensure that the lenses prescribed to patients match their visual needs.

The other options do not reflect the primary function of a lensmeter. Adjusting the frame fit involves physical alterations to the eyeglass frame rather than measuring lens power. Testing lens durability pertains to the lens' resistance to scratches and impacts, which is not a function of a lensmeter. Calculating the base curve of a lens relates to the curvature where light enters and exits the lens but is not directly measured by a lensmeter; this is typically determined during the lens manufacturing process or with specific curvature measuring tools.