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Induced Prism

Induced Prism. California State Society for Opticians February 12, 2017. What is Induced Prism?. If a pair of spectacles were received with the following: Incorrect PD Measurements Power of the Rx ANSI Standards We may have to remake the spectacles. Let’s Identify a Prism by Lenses Design.

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Induced Prism

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  1. Induced Prism California State Society for Opticians February 12, 2017

  2. What is Induced Prism? • If a pair of spectacles were received with the following: • Incorrect PD Measurements • Power of the Rx • ANSI Standards • We may have to remake the spectacles

  3. Let’s Identify a Prism by Lenses Design Apex Plus Lenses Base Base Base Apex Apex Apex Minus Lenses Thickness located at the Base Base

  4. dD 10    Prentice Rule Calculating Unwanted Prism Prentice Rule Formula Prism = Power x Decentration (cm) 10 P

  5. dD 10    P Short Cuts Notice: Multiply by .3, because when we divide 3/10 = .3 When taking the exam just move the decimal to the left. Example How much prism is created when a 4.50 D lens is moved 5 mm? Answer: 4.50 D x .5 cm = 2.25 of prism Example How much prism is created when a 2.50 D lens is moved 3 mm? Answer: 2.50 D x .3 cm = .75 of prism

  6. Direction of Prism Base IN; Base OUT; Base UP; Base Down When the Rx is written with Negative Sphere, example: -1.50, -2.50, -5.50 the Direction of Prism is OPPOSITE When the Rx is written with Positive Sphere, example: +2.50, +0.25, +6.50 the Direction of SAME Direction of Prism

  7. How much prism is induced with Rx -3.00 if moved OUT 3 mm? • Lenses with a -4.00 moved 5 mm IN, how much prism? • Lenses with a +3.50 moved 6 mm AWAY, how much prism is induced? • Lenses with a +6.50 moved 4 mm NASUALLY, how much prism is induced? • How much prism is induced with an Rx -1.50 that moved TEMPORALLY 4 mm?

  8. A pair of spectacles where made with PD of 66, but the patient PD is 62 how much prism is induced and in which direction?Rx: OD -3.50 OS: -2.50 • The lab cut lenses with an OC of 61, and the patient PD is 65 how much induced prism is created and in which direction?Rx: OD – 2.50 OS: +1.00 • Patient’s PD is 59 and lenses were cut to a frame PD of 66, how much prism is induced and in which direction? Rx: OD +0.25 OS: +1.50 • Lenses with a +6.00 were made 3 mm out, how much prism is induced and in which direction? • Lenses with a -3.00 moved 5 mm in, how much prism is induced and in which direction? • Lenses with a +7.50 moved 8 mm out, how much prism is induced and in which direction? • Lenses with a +1.50 moved 6 mm in, how much prism is induced and in which direction? For answers to the above contact the California State Society for Opticians at email: California.Society.Opticians@gmail.com

  9. A pair of spectacles where made with PD of 65, but the patient PD is 63 how much prism is induced and in which direction?Rx: OD -4.50 OS: -3.50 The lab cut lenses with an OC of 60, and the patient PD is 64 how much induced prism is created and in which direction?Rx: OD – 2.50 OS: +1.00 Patient’s PD is 59 and lenses were cut to a frame PD of 66, how much prism is induced and in which direction? Rx: OD +0.25 OS: +1.50 Lenses with a +3.00 were made 4 mm out, how much prism is induced and in which direction? Lenses with a -4.00 moved 6 mm in, how much prism is induced and in which direction? Lenses with a +8.50 moved 4 mm out, how much prism is induced and in which direction? Lenses with a +3.50 moved 3 mm in, how much prism is induced and in which direction? For answers to the above contact the California State Society for Opticians at email: California.Society.Opticians@gmail.com

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