ABO NOCE Basic Opticianry Prescription Transposition 3

Question 1

What does the power cross represent in ophthalmic optics?

Accepted Answer

The lens power in the two principal meridians

Answer

A power cross is a diagram showing the power in each of the two principal (90°-apart) meridians of a lens.

Question 2

Convert the power cross (+1.00 @ 090 / -0.50 @ 180) to a spectacle prescription in minus cylinder form.

Accepted Answer

+1.00 -1.50 x 090

Answer

The highest minus power meridian (180°) has -0.50, and the difference is -1.50 cyl; sphere = power at axis meridian (090) = +1.00.

Question 3

Transpose +2.50 -3.00 x 180. What is the result?

Accepted Answer

-0.50 +3.00 x 090

Answer

New sphere = +2.50 - 3.00 = -0.50; new cyl = +3.00; new axis = 180 - 90 = 090.

Question 4

A lens has -2.00 D power at 180° and -4.00 D power at 090°. Written in plus cylinder form, the cylinder power is:

Accepted Answer

+2.00

Answer

In plus cylinder form, cylinder = more positive meridian minus more negative meridian = -2.00 - (-4.00) = +2.00.

Question 5

Which prescription is equivalent to -1.00 +2.00 x 060?

Accepted Answer

+1.00 -2.00 x 150

Answer

Transpose: new sphere = -1.00 + 2.00 = +1.00; new cyl = -2.00; new axis = 060 + 90 = 150.

ABO NOCE Basic Opticianry Practice Test