Ophthalmic Optics and Principles Questions and Answers Flashcards
7 cards from real ABO NOCE Basic Opticianry practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
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Prentice's Rule states that prism power (Δ) equals lens power (D) multiplied by which factor?
Answer: The decentration in centimeters
Prentice's Rule: Δ = D × c, where c is the decentration in centimeters.
Which surface of a lens is defined as the back vertex power measurement used clinically to verify prescriptions?
Answer: Back vertex power
Back vertex power (BVP) is the standard clinical measurement taken from the back surface of a lens and used to verify prescriptions.
A lens with a base curve of +6.00 D and a back surface of −3.50 D has an approximate power of:
Answer: +2.50 D
Approximate lens power ≈ front surface + back surface = +6.00 + (−3.50) = +2.50 D.
Which optical principle explains why higher index lenses can be made thinner than lower index lenses for the same prescription?
Answer: Lensmaker's equation
The Lensmaker's equation shows that higher index materials refract more strongly, allowing less curvature (and thus thinner lenses) to achieve the same power.
What is the vergence of light rays that are parallel (coming from optical infinity)?
Answer: 0.00 D
Parallel rays from optical infinity have zero vergence (neither converging nor diverging).
In ophthalmic optics, what does the term 'transposition' refer to?
Answer: Converting plus cylinder form to minus cylinder form (or vice versa)
Transposition is the mathematical process of rewriting a prescription from plus cylinder form to minus cylinder form or vice versa without changing its optical effect.
A -4.00 D lens placed 12 mm from the eye. If moved to 0 mm (contact lens), the effective power at the cornea is approximately:
Answer: -3.82 D
Effective power = F / (1 − d×F) = −4.00 / (1 − 0.012 × (−4.00)) = −4.00 / 1.048 ≈ −3.82 D.