ABO NOCE Basic Opticianry Prescription Transposition 3 — Questions and Answers
Question 1: What does the power cross represent in ophthalmic optics?
- The lens power in the two principal meridians (Correct answer)
- The optical center of a lens
- The prism base direction
- The segment height of a bifocal
Correct answer: The lens power in the two principal meridians
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.
- +1.00 -1.50 x 090 (Correct answer)
- -0.50 +1.50 x 180
- +1.00 +1.50 x 180
- -0.50 -1.50 x 090
Correct answer: +1.00 -1.50 x 090
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?
- -0.50 +3.00 x 090 (Correct answer)
- +2.50 +3.00 x 090
- -0.50 -3.00 x 090
- +0.50 +3.00 x 090
Correct answer: -0.50 +3.00 x 090
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:
- +2.00 (Correct answer)
- -2.00
- +4.00
- -6.00
Correct answer: +2.00
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?
- +1.00 -2.00 x 150 (Correct answer)
- -1.00 -2.00 x 060
- +1.00 +2.00 x 150
- -1.00 +2.00 x 150
Correct answer: +1.00 -2.00 x 150
Transpose: new sphere = -1.00 + 2.00 = +1.00; new cyl = -2.00; new axis = 060 + 90 = 150.
Question 6: When a prescription is written in plus cylinder form, the cylinder axis is aligned with:
- The meridian of least power (most minus) (Correct answer)
- The meridian of greatest power (most plus)
- The optical center
- The prism reference point
Correct answer: The meridian of least power (most minus)
In plus cylinder notation, the axis indicates the meridian with the least (most minus) power; the cylinder adds power 90° away.
Question 7: Transpose plano +1.75 x 045 into minus cylinder form.
- +1.75 -1.75 x 135 (Correct answer)
- plano -1.75 x 135
- +1.75 +1.75 x 135
- -1.75 +1.75 x 045
Correct answer: +1.75 -1.75 x 135
New sphere = 0.00 + 1.75 = +1.75; new cyl = -1.75; new axis = 045 + 90 = 135.
ABO NOCE Basic Opticianry Prescription Transposition 3
What does the power cross represent in ophthalmic optics?