Free ABO-NOCE Spectacle Lens Aberrations Questions and Answers

Question 1

A patient wearing high-plus spherical lenses complains that straight lines appear curved inwards, especially at the edges of the lens. This is a classic example of which aberration?

Accepted Answer

Pincushion Distortion

Answer

Pincushion distortion is caused by the magnification increasing from the center to the periphery of a plus lens. This makes straight lines viewed through the lens periphery appear to curve inwards towards the center. Barrel distortion, the opposite effect, is common in high-minus lenses.

Question 2

Which lens property is measured by the Abbe value, and what aberration does a low Abbe value indicate a higher amount of?

Accepted Answer

Abbe Value; Chromatic Aberration

Answer

The Abbe value is a measure of a lens material's chromatic dispersion. A lower Abbe value signifies more dispersion, which results in more prominent chromatic aberration, seen as color fringing around objects.

Question 3

Spherical aberration results in light rays passing through the periphery of a lens focusing at a different point than rays passing through the center. This aberration is most effectively minimized by using what type of lens design?

Accepted Answer

An aspheric lens

Answer

Aspheric lens designs gradually change in curvature from the center to the edge. This change is calculated to correct for spherical aberration, allowing parallel light rays to focus at a single point, resulting in sharper vision.

Question 4

When a wearer looks away from the optical center of a lens at an angle, they may experience blur. This is caused by light hitting the lens obliquely, creating two separate focal lines. What is this aberration called?

Accepted Answer

Marginal Astigmatism

Answer

Marginal astigmatism, also known as oblique astigmatism or radial astigmatism, occurs when viewing through the periphery of a lens. It is a significant off-axis aberration that corrected-curve lens designs aim to minimize.

Question 5

A comet-shaped blur or flare extending from a point of light, viewed off-axis, is characteristic of which monochromatic aberration?

Accepted Answer

Coma

Answer

Coma is an off-axis aberration that causes points of light to be imaged as a comet-like shape. The 'tail' of the comet points either away from or towards the optical axis, depending on whether it is positive or negative coma.

ABO NOCE Basic Opticianry Practice Test

ABO NOCE Basic Opticianry Practice Test

Free ABO-NOCE Spectacle Lens Aberrations Questions and Answers