ABO NOCE Basic Opticianry Ophthalmic Lenses and Materials Questions and Answers 5

Question 1

Which lens form is said to be in 'best form' (corrected curve) configuration?

Accepted Answer

A lens where the base curve is chosen to minimize oblique astigmatism for the given power

Answer

Best form (corrected curve) lenses use a specific base curve for each power to minimize peripheral aberrations such as oblique astigmatism.

Question 2

In a toric lens, the two principal meridians are always:

Accepted Answer

Perpendicular to each other

Answer

A toric surface has two principal meridians of maximum and minimum curvature that are always 90° apart.

Question 3

What is the purpose of an 'edging allowance' when ordering a lens blank?

Accepted Answer

Additional blank diameter to ensure the prescription can be cut to fit the frame shape

Answer

The edging allowance ensures the blank is large enough so the prescription area extends fully to all edges of the traced frame shape.

Question 4

Minus lenses are thicker at the:

Accepted Answer

Edge (periphery)

Answer

Minus (concave) lenses are thinnest at the center and increase in thickness toward the edges.

Question 5

What is 'lens clock' (lens measure) used to measure?

Accepted Answer

The surface curvature (base curve) of a lens surface

Answer

A lens clock (lens measure) measures the surface power/curvature of a lens by sensing the sagittal depth across a fixed chord.

ABO NOCE Basic Opticianry Practice Test