ABO NOCE Basic Opticianry Ophthalmic Optics Questions and Answers 2 — Questions and Answers
Question 1: A lens with a power of +2.00 D has a focal length of:
- 25 cm
- 50 cm (Correct answer)
- 100 cm
- 200 cm
Correct answer: 50 cm
Focal length (in meters) equals 1 divided by power in diopters; 1/2.00 = 0.50 m = 50 cm.
Question 2: Chromatic aberration in ophthalmic lenses is caused by:
- Incorrect base curve selection
- Dispersion of light into its spectral components by the lens material (Correct answer)
- Excessive center thickness
- Prism induced by decentration
Correct answer: Dispersion of light into its spectral components by the lens material
Different wavelengths of light refract at slightly different angles through a lens, causing chromatic aberration due to material dispersion.
Question 3: The Abbe value (V-number) of a lens material is used to measure its:
- Refractive index
- Resistance to chromatic aberration (Correct answer)
- Impact resistance
- UV absorption
Correct answer: Resistance to chromatic aberration
A higher Abbe value indicates less chromatic aberration; it measures how well a material keeps colors together.
Question 4: Which type of lens surface eliminates the tangential and sagittal focus errors simultaneously?
- Spherical
- Toric
- Atoric (Correct answer)
- Lenticular
Correct answer: Atoric
Atoric surfaces are designed to correct both tangential and sagittal oblique astigmatic errors simultaneously.
Question 5: The refractive index of standard CR-39 plastic lens material is approximately:
- 1.40
- 1.50 (Correct answer)
- 1.60
- 1.74
Correct answer: 1.50
CR-39 (allyl diglycol carbonate) has a refractive index of approximately 1.499, commonly cited as 1.50.
Question 6: When light travels from a denser medium into a less dense medium at an angle exceeding the critical angle, what occurs?
- Refraction
- Total internal reflection (Correct answer)
- Diffraction
- Absorption
Correct answer: Total internal reflection
Total internal reflection occurs when light hits the interface at or beyond the critical angle, with no light passing through.
Question 7: The sagittal depth (sag) of a lens surface is defined as:
- The distance from the optical center to the lens edge
- The perpendicular distance from the chord to the surface apex (Correct answer)
- The thickness at the geometric center
- The radius of curvature of the surface
Correct answer: The perpendicular distance from the chord to the surface apex
Sag is the depth of the curve — the perpendicular distance from a flat chord across the lens to the curved surface.
ABO NOCE Basic Opticianry Ophthalmic Optics Questions and Answers 2
A lens with a power of +2.00 D has a focal length of: