Prescription Transposition Flashcards
7 cards from real ABO NOCE Basic Opticianry practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Prescription Transposition flashcards as text
What does the power cross represent in ophthalmic optics?
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.
Convert the power cross (+1.00 @ 090 / -0.50 @ 180) to a spectacle prescription in minus cylinder form.
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.
Transpose +2.50 -3.00 x 180. What is the result?
Answer: -0.50 +3.00 x 090
New sphere = +2.50 - 3.00 = -0.50; new cyl = +3.00; new axis = 180 - 90 = 090.
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:
Answer: +2.00
In plus cylinder form, cylinder = more positive meridian minus more negative meridian = -2.00 - (-4.00) = +2.00.
Which prescription is equivalent to -1.00 +2.00 x 060?
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.
When a prescription is written in plus cylinder form, the cylinder axis is aligned with:
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.
Transpose plano +1.75 x 045 into minus cylinder form.
Answer: +1.75 -1.75 x 135
New sphere = 0.00 + 1.75 = +1.75; new cyl = -1.75; new axis = 045 + 90 = 135.