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
Transpose the following prescription into plus cylinder form: +1.50 -2.00 x 090
Answer: -0.50 +2.00 x 180
To transpose, first combine the sphere and cylinder powers to get the new sphere (+1.50 + -2.00 = -0.50). Second, change the sign of the cylinder (-2.00 becomes +2.00). Third, change the axis by 90 degrees (90 + 90 = 180).
Transpose the following prescription into minus cylinder form: -3.00 +1.25 x 170
Answer: -1.75 -1.25 x 080
To transpose to minus cylinder, first find the new sphere by adding the sphere and cylinder (-3.00 + +1.25 = -1.75). Next, change the cylinder sign (+1.25 becomes -1.25). Finally, change the axis by 90 degrees (170 - 90 = 080).
What is the spherical equivalent of the prescription +2.25 -1.50 x 120?
Answer: +1.50 D
The spherical equivalent is calculated by adding half of the cylinder power to the sphere power. In this case: +2.25 + (-1.50 / 2) = +2.25 + (-0.75) = +1.50 D.
Transpose the prescription Plano +2.50 x 030 into minus cylinder form.
Answer: +2.50 -2.50 x 120
Start with the sphere (0.00) and add the cylinder (+2.50) to get the new sphere: +2.50. Change the cylinder sign to minus: -2.50. Change the axis by 90 degrees: 30 + 90 = 120. The result is +2.50 -2.50 x 120.
Which of the following prescriptions is optically identical to -1.00 -1.00 x 045?
Answer: -2.00 +1.00 x 135
To find the optically identical prescription, you must transpose the original. New sphere: -1.00 + (-1.00) = -2.00. New cylinder: +1.00. New axis: 45 + 90 = 135. The transposed prescription is -2.00 +1.00 x 135.
Transpose the prescription +4.75 +0.75 x 110 into minus cylinder form.
Answer: +5.50 -0.75 x 020
Combine the sphere and cylinder for the new sphere: +4.75 + 0.75 = +5.50. Change the cylinder sign: -0.75. Change the axis by 90 degrees: 110 - 90 = 020. The result is +5.50 -0.75 x 020.
When transposing a prescription from minus to plus cylinder form, the new sphere power will always be:
Answer: More minus (or less plus) than the original sphere
The new sphere is calculated by algebraically adding the original sphere and cylinder. Since you are starting with a minus cylinder, you will be adding a negative number to the sphere, which will always result in a new sphere power that is more minus (or less plus) than the original.