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It is frequently expedient to demonstrate the nature of bifocal lenses to a patient who is considering them for the first time. I have found a convenient method in the form of flat bifocal lenses made up to fit the standard trial case rims. The distance base is a plano lens, and the lower segment is a Kryptok circular addition; this type of segment lends itself readily to a flat base. The segment is so placed in the rim that when the handle is upright the reading center is displaced nasally 1.5 mm. The lenses are slipped into the trial frames behind the distance correction, and the patient is instructed to read Jaeger's test type and then to glance around the room. For correction of near vision, additions consisting of a pair of + 0.75, + 1.25 or + 1.75 spheres seem to answer the ordinary requirements. Patients needing additions of more than
Friedman B. DEMONSTRATION BIFOCAL LENSES FOR TRIAL CASE. Arch Ophthalmol. 1939;22(2):288. doi:10.1001/archopht.1939.00860080132012
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