ABO NOCE Basic Opticianry Ophthalmic Optics Questions and Answers 3 — Questions and Answers
Question 1: A prism displaces light toward its:
- Apex
- Base (Correct answer)
- Optical center
- Edge
Correct answer: Base
Light bends toward the base of a prism, while the image appears displaced toward the apex.
Question 2: In the spectacle magnification formula, which factor relates to the power of the lens?
- Shape factor
- Power factor (Correct answer)
- Vertex distance factor
- Prism factor
Correct answer: Power factor
The power factor component of spectacle magnification accounts for the vergence-changing effect of the lens power.
Question 3: Which of the following best describes the term 'vergence' as used in ophthalmic optics?
- The bending of light at a lens surface
- The curvature of a wavefront of light (Correct answer)
- The angle of incidence of a light ray
- The thickness of a lens at its edge
Correct answer: The curvature of a wavefront of light
Vergence describes the degree of convergence or divergence of a wavefront and is measured in diopters.
Question 4: The nominal power of a lens is calculated using which formula?
- F = n/r
- F = (n₂ - n₁)/r (Correct answer)
- F = 1/f
- F = F₁ + F₂ - (t/n)F₁F₂
Correct answer: F = (n₂ - n₁)/r
Surface power is calculated as F = (n₂ - n₁)/r, where n values are the refractive indices and r is the radius of curvature in meters.
Question 5: When a convex lens is placed in contact with a concave lens of equal but opposite power, the result is:
- A stronger convex lens
- A plano (zero power) lens (Correct answer)
- A prismatic lens
- A bifocal lens
Correct answer: A plano (zero power) lens
Equal and opposite powers cancel each other out, resulting in a lens system with zero net power (plano).
Question 6: The critical angle for total internal reflection depends primarily on:
- The wavelength of the incident light only
- The refractive indices of both media at the interface (Correct answer)
- The thickness of the denser medium
- The angle of incidence only
Correct answer: The refractive indices of both media at the interface
The critical angle is calculated using sin(θc) = n₂/n₁, depending on the refractive indices of both materials at the interface.
Question 7: Which lens form produces the least oblique astigmatic error for a given prescription?
- Flat form (plano front)
- Corrected curve (best form) (Correct answer)
- Meniscus with steep back curve
- Equiconvex form
Correct answer: Corrected curve (best form)
Best-form (corrected curve) lenses are designed with base curves that minimize oblique astigmatic error for each prescription power.
ABO NOCE Basic Opticianry Ophthalmic Optics Questions and Answers 3
A prism displaces light toward its: