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1 Prentice's Rule formula: 2 How to find decenteration per lens?
When the Seg Ht is below the Datum
3 Base Curve Rule of Thumb plus: 4
line the direction means:
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Prentice's Rule formula: P(diopter prism) = F (D) x d (cm)
P=FxDec (mm) / 10
Vogel's Rule formula:
, Plus Base Curve formula: BC=SE + 4.00
(If the biggest true power is a plus, +4.00 to that
number)
Spherical Equivalent formula: SE= Sph + 1/2 x Cyl
Base Curve Rule of Thumb plus: (Plus)
If the biggest (or only) true power is a plus, add +4.00
to that number.
Base Curve Rule of Thumb minus: (Minus)
•If the biggest (or only) true power is up to a -8.00,
combine the true power w/ a +8.00
•If the biggest (or only) true power is between -8.12
and -15.00, use a Plano base curve rule
•If the biggest (or only) true power is over -15.00, a
specialty lens is likely needed.
Plus lens moved away for the eye: Gains power
(Remember magnifying glass)
Plus lens moved close to the eye: Loses power
A minus lens moved away from the Loses power
eye:
A minus lens moved close from the Gains power
eye:
How to find FPD? (Frame PD) FPD= Frame A (width) + DBL
How to find Total decenteration? TTD= FPD - PT PD
How to find decenteration per lens? Per lens= FPD - PT PD / 2