In a prior paper1 I advocated that the refractionist be conversant with the different types and makes of bifocal lenses and the individual optical attributes which qualify or disqualify any of them for a particular prescription.
This presentation supplements the preceding one. A few essentials will be reviewed.
REVIEW OF PREVIOUS ARTICLE
The eye is confronted by a prism not only when a prism is placed in front of it but also it must look through a lens at any eccentric point.The modern bifocal lens is synthetic. The distance lens enters into the structure of the bifocal lens, and in reading, the line of sight passes unavoidably through an infracentric point.In my previous work I assumed that the upper edge of a contemplated segment is 4 mm. below the optical center of the distance component and the reading level down an additional 4 mm., a natural reading
OLSHO SL. VERTICAL PRISM IMBALANCES IN BIFOCAL LENSES COEXISTENT WITH HYPERPHORIA. Arch Ophthalmol. 1939;21(3):515–521. doi:10.1001/archopht.1939.00860030123015
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