Ophthalmic Optics and Principles 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.
Read the first 7 Ophthalmic Optics and Principles flashcards as text
Which lens form has the same power on both surfaces but with one surface convex and the other concave?
Answer: Meniscus
A meniscus lens has one convex and one concave surface, giving it a crescent-like cross-section.
What is the term for the bending of light as it passes from one medium to another of different optical density?
Answer: Refraction
Refraction is the change in direction of light as it crosses the boundary between two media with different indices of refraction.
If a lens has a back vertex power of +3.00 D and a front vertex power of +2.75 D, which power is used when verifying the prescription with a lensometer?
Answer: Back vertex power
The back vertex power is the standard used for lensometer verification because it represents the effective power at the back surface closest to the eye.
What happens to the critical angle when light travels from glass (n=1.5) into air (n=1.0)?
Answer: It is approximately 41.8°
Using sin(c) = n2/n1 = 1.0/1.5, the critical angle for glass-to-air is approximately 41.8°.
A prism with apex angle 10° and refractive index 1.5 produces approximately how much deviation in diopters (prism diopters)?
Answer: 10Δ
Prentice's approximation: P = a(n-1) × 100, so 10 × 0.5 = 5°, but in prism diopters at thin prism approximation, deviation ≈ 10Δ for an apex of 10° with n=1.5.
What is the vergence of light rays that are parallel to the optical axis before entering a lens?
Answer: Zero vergence
Parallel rays have zero vergence because they neither converge nor diverge; they come from optical infinity.
In ophthalmic optics, the term 'base curve' most commonly refers to which lens surface?
Answer: The front convex surface
The base curve is the front (convex) surface curve of an ophthalmic lens, which determines the lens form.