When converting a plus cylinder Rx to a minus cylinder Rx, by how many degrees should the axis be adjusted?

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Prepare for the Shopko Optician Certification Test. Study with flashcards and multiple choice questions. Enhance your knowledge with detailed explanations and get ready to excel in your exam!

Multiple Choice

When converting a plus cylinder Rx to a minus cylinder Rx, by how many degrees should the axis be adjusted?

Explanation:
In astigmatism prescriptions, the axis designates the meridian with no cylindrical power, while the cylinder adds power to the perpendicular meridian (90 degrees away). To keep the same overall correction when switching from plus cylinder to minus cylinder, you rotate the axis by 90 degrees, so the cylinder’s effect remains aligned with the same meridians. Practically, you take the original axis and add 90 degrees (wrapping around at 180 if needed). This means the axis should be adjusted by 90 degrees.

In astigmatism prescriptions, the axis designates the meridian with no cylindrical power, while the cylinder adds power to the perpendicular meridian (90 degrees away). To keep the same overall correction when switching from plus cylinder to minus cylinder, you rotate the axis by 90 degrees, so the cylinder’s effect remains aligned with the same meridians. Practically, you take the original axis and add 90 degrees (wrapping around at 180 if needed). This means the axis should be adjusted by 90 degrees.

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