ABO NOCE Basic Opticianry Ophthalmic Optics Questions and Answers 5 — Questions and Answers
Question 1: The optical cross is a diagram used to represent:
- The prismatic effect of a lens
- The power in two principal meridians of a spherocylindrical lens (Correct answer)
- The base curve and sag of a lens
- The vertex distance correction
Correct answer: The power in two principal meridians of a spherocylindrical lens
An optical cross shows the power in each of the two principal meridians (90° apart) of a spherocylindrical lens.
Question 2: When comparing two lenses of equal power, the lens with a higher refractive index will be:
- Thicker and heavier
- Thinner and lighter (Correct answer)
- The same thickness but lighter
- Thinner but heavier
Correct answer: Thinner and lighter
Higher refractive index materials bend light more per unit of surface curvature, allowing flatter, thinner lens designs.
Question 3: The lensometer (focimeter) measures a lens by finding the position where:
- The lens reflects the maximum amount of light
- The target image is focused at a fixed reference point corresponding to a specific vergence (Correct answer)
- The lens produces no prismatic displacement
- The chromatic aberration is eliminated
Correct answer: The target image is focused at a fixed reference point corresponding to a specific vergence
The lensometer neutralizes the lens power by finding the position where the target appears clear, corresponding to the vergence added by the lens.
Question 4: Oblique astigmatism as a lens aberration is different from astigmatism in a prescription because it:
- Only affects the horizontal meridian
- Is introduced by the lens itself when viewing off-axis, not from the eye's refractive error (Correct answer)
- Cannot be corrected with spectacle lenses
- Only occurs in minus lenses
Correct answer: Is introduced by the lens itself when viewing off-axis, not from the eye's refractive error
Oblique (marginal) astigmatism is a lens aberration occurring when light passes through the peripheral zone at an angle, unrelated to the wearer's astigmatism.
Question 5: The reduced eye model simplifies the eye to a single refracting surface with a refractive index of approximately:
- 1.336 (Correct answer)
- 1.000
- 1.523
- 1.760
Correct answer: 1.336
The reduced eye model uses a single refracting surface with the refractive index of the ocular media, approximately 1.336.
Question 6: When solving for the cross-cylinder power used to refine cylinder axis and power, the examiner adds a lens whose:
- Spherical power equals the working distance correction
- Principal meridians are at 45° to the correcting cylinder axis (Correct answer)
- Axis aligns exactly with the suspected cylinder axis
- Power equals half the estimated cylinder error
Correct answer: Principal meridians are at 45° to the correcting cylinder axis
A Jackson Cross Cylinder (JCC) is placed with its principal meridians at 45° to the trial cylinder axis to test axis, then straddling it to test power.
Question 7: Which of the following describes a plano-convex lens?
- Both surfaces are convex
- One surface is flat and the other is convex (Correct answer)
- Both surfaces are concave
- One surface is convex and the other is concave
Correct answer: One surface is flat and the other is convex
A plano-convex lens has one flat (plano) surface with zero curvature and one convex surface, giving it positive (converging) power.
ABO NOCE Basic Opticianry Ophthalmic Optics Questions and Answers 5
The optical cross is a diagram used to represent: