OPTICAL MATH MADE EASY!

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9/4/2013Lens Power Compared toFocal LengthLens PowerFocal Length0.5 D 2 m (200 cm)1.0 D 1 m (100 cm)2.0 D 0.50 m (50 cm)3.0 D 0.33 m (33 cm)4.0 D 0.25 m (25 cm)5.0 D 0.20 m (20 cm)6.0 D 0.17 m (17 cm )7.0 D 0.14 m (14 cm)8.0 D 0.13 m (13 cm)9.0 D 0.11 m (11 cm)10.0 D 0.10 m (10 cm)The Optical Cross• A spherical lens has one power.• A spherocylindrical lens has one spherical and onecylindrical surface, giving it 2 radii of curve (unequalpower).• An optical cross is used to illustrate the powers of aspherocylindrical lens.Remember: The power of the cylinder is found 90degrees away from the placement of the axis.The Optical Cross+3.00 +1.00 +4.00+3.00 0 +3.00Rx: +3.00 +1.00 x 180No part of this document can be copied with out permission from EyeTrain4You, Inc. 8
9/4/2013The Optical Cross-4.00 0 -4.00-4.00 +1.00 -3.00Rx: -4.00 +1.00 x 090Now You Do It-1.00 +1.00-1.00 0What is the prescription?Prentice’s RuleIf the patient is not looking through theoptical center of a lens that has power, theyare looking through prism.Optical CenterInduced PrismNo part of this document can be copied with out permission from EyeTrain4You, Inc. 9
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