Multifocal Designs
Fused & One Piece Designs and Practice Exercies

Fused			One Piece
Round Flat Top			Ultex Franklin (Executive) Progressive

Glass multifocal lenses may be either of a fused or one piece design. As the name suggests, one piece multifocals are manufactured from one piece of glass where the additional power through the reading zone is achieved through variations in the surface curvature. Fused multifocals are manufactured by fusing a higher index material such as barium glass (n= 1.60) to a lower index material such as crown glass (n= 1.523). The result is more plus power through the segment portion of the lens. The table above applies to any size bifocal or trifocal falling in the various categories. For example a fused flat top multifocal applies to any size bifocal, trifocal, or occupational lens previously mentioned.

Hard resin lenses are manufactured through a molding process and typically consist of only one material (CR-39). Therefore they may be considered one piece lenses. The one piece design of resin flat top segments account for the ledge along the transition line separating the carrier lens from the segment which is absent in a fused glass lens of the same style.

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Practice Exercies
Determine the power through the reading portion of the following bifocal prescriptions.

1.)		+2.00 - 0.50 x 030 +1.75 - 0.25 x 010 Add: +1.50 O.U.	2.)		+0.50 - 0.75 x 045 +0.25 - 0.25 x 180 Add: +1.25 O.U.
3.)		-2.50 - 1.00 x 090 -2.75 - 1.50 x 110 Add: +2.50
The following prescriptions indicate the distance power and the full reading addition. In each instance you have been requested to make one pair of intermediate powered single vision vocational lenses utilizing 50% of the add power. What lens powers are needed to achieve this purpose?
4.)		+3.50 - 0.75 x 025 + 3.75 - 0.50 x 005 Add: +2.50
5.)		-5.00 - 1.75 x 175 -5.75 - 2.00 x 180 Add: +2.00	6.)		+7.50 + 2.75 x 090 +7.75 + 2.50 x 110 Add: +1.50

(answers on last page)