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ABO Numbers, Math, and Formulas Exam Practice Questions and Verified Answers – Comprehensive Opticianry Mathematics Study Guide

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This document provides a focused study guide for the ABO (American Board of Opticianry) Exam, featuring practice questions and verified answers covering the numerical, mathematical, and formula-based concepts used in opticianry. It covers optical calculations, lens power, prism, transposition, vertex distance, magnification, focal length, diopters, measurements, and other essential ophthalmic formulas. The material is designed to strengthen calculation skills and support preparation for the mathematics and optics portions of the ABO certification examination.

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1. Prentice's Rule: P = f ẋ c P =
amount of prism correction
f = lens power (in diopters)
c = decentration (the distance between the pupil centre and the lens's optical centre, in millimeters)
2. Cornea IOR: 1.37
3. Tear Film, Vitreous IOR: 1.33
4. Crystalline lens IOR: 1.42
5. Optical Standard indeẋ of refraction: 1.53
6. Crown Glass indeẋ of refraction: 1.523
7. High indeẋ IOR: 1.74
8. CR-39 IOR: 1.49 - 1.50
9. Poly indeẋ of refraction: 1.586
10. Air IOR: 1.00
11. How fast does light travel through air: 186,000 mi/sec
12. Minimum Blank Size (MBS) formula: (GCD - PD) + ED A +
DBL + ED - PD
Frame PD - PD + ED Dec.
+ ED
GCD = geometric center distance or A + DBL PD =
Pt. PD
ED = ettective diameter
Dec. = Decentration
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, 13. Focal length formula, diopters known: 1/Dioptic Power
14. Dioptic Power formula, foci known: 1/Focal Length (m)
15. Anisometropia: Ditterence of 2 diopters between OD & OS
16. What is the Radius of a 1 diopter curve?: 530mm
17. Radius formula: 530/Power = R
18. Power formula: 530/Radius = Diop.
19. Vertical Decentration formula: Seg.ht. - B/2 OC
height - (B measurement / 2)




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