Determining the vertical and horizontal positioning of multifocal and progressive lenses.

The key to success with any ophthalmic spectacle prescription is not only the accurate determination of the refractive prescription, but the proper selection and fitting of the ophthalmic frame and lenses. Proper selection and fitting are especially important with bifocals, trifocals, or progressive lenses, which present many variables other than inaccurate interpupillary distance measurement that can lead to patient dissatisfaction. This article discusses fitting procedures for patients with new or existing multifocals. It reviews how to determine proper multifocal segment heights; and calculate distant decentration, inset, and total inset measurements; and it addresses issues involving variations in frame size and patient temperament.