16 CFR Part 456 ; Agency Information Collection Activities: Review; Comment Request Ophthalmic Practice Rule (Eyeglass Rule): FTC Project No. R511996
In the past all spectacle lenses were made of the same index of refraction (density), same center, edge thickness and the same style. All of the patients facial anatomical measurements were taken with a millimeter ruler at the time of the eye examination. With the explosion of new frame designs, lens materials and technologies, the old measurement system is no longer remotely adequate. Proper placement of the appropriate aspect of the lens in front of the patients pupil is critically important for today's technologically more advanced spectacle lense and frame materials. Special instrumentation and devices are required to ensure the prescription lenses will function properly for the patient. The measurements must be made relative to the eyeglass frame selected. Therefore, the patient must be measured by the seller and/or the dispenser of the eyeglass frame. The optometrist cannot assume any responsibility for the proper prescription being misplaced in front of the pupil due to the configuration of the frame, the lens style or material chosen by the patient. Not all lenses are created equal and there are many technological differences. Pupillary distance, "PD", refers to the measured distance between the patients pupils, and is taken for at least far and near viewing distances. Today's lenses require precise horizontal and vertical placement of the lens selected by the patient. These measurements are effected by the lens and frame shape, size and use (driving, computer or reading) of the prescription. Therefore, the patient must be measured by the seller and/or dispenser of the eyeglass frame. Segment height, bifocal, trifocal or progressive lenses, refers to the height or placement of the near viewing (intermediate or reading portion) of the lens. Most lens manufacturers have a fitting guide to ensure the lens is positioned for maximum viewing efficiency with minimum of peripheral distortion. Therefore, the patient must be measured by the seller and the dispenser of the eyeglass frame.