Double masked study of progressive addition lenses.

Fifty-four patients, selected to encompass the full range of bifocal additions were involved in a double masked study of Varilux II and Ultravue progressive addition lenses in which neither patient in or examiner knew the type of lens prescribed at a given trial. Measurements of width of near field were taken with each type prior to and following wearing periods of one month each. Subjects had complete freedom to select or substitute a form of bifocal of their own choice without extra costs. The paper indicates the selections made, and considers the variables influencing these choices. The final results imply that acceptance of variable focus lenses may rest more with the bias of the practitioner than the readiness of the patient.