Bifocals Facts- incomplete go over ppt

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Last updated 8:27 PM on 7/9/26
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5 Terms

1
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Describe today’s Bifocals

Downforce solid plastic bifocals with segment on front surface, back powered for prescription

2
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What are fused bifocals?

  • The depression curve is cut into the lens, high index glass button heated until fused.

  • No step

  • Addition is created by: segment having higher refractive index (more +ve), thickness (more +ve), Fcon (interface between depression curve and segment button

3
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What are Solid bifocals?

  • Made from one material

  • Addition is achieved by diff surface powers

  • Has a step

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What are the fitting rules for bifocals?

The segment extreme point should align with the lower limbus (higher if mainly for reading and vice versa)

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How do you calculate geometric inset?

E.g.

D PD = 66

N PD = 62

Inset is 2mm in each eye