If axis 135 is transposed to minus cylinder, what is the new axis?

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Prepare for the Certified Paraoptometric Assistant (CPOA) Exam. Study with extensive flashcards and multiple choice questions with explanations. Enhance your skills and knowledge to succeed.

Multiple Choice

If axis 135 is transposed to minus cylinder, what is the new axis?

Explanation:
In ophthalmic lens notation, converting from plus cylinder to minus cylinder keeps the same optical effect but shifts the axis by 90 degrees. The axis marks the meridian with no cylindrical power, and switching to minus cylinder swaps which meridian carries the power, so the axis becomes perpendicular to the original. An axis of 135 degrees is perpendicular to 45 degrees (since 135 plus or minus 90 equals 45, and axes are modulo 180). Therefore, the new axis is 45 degrees.

In ophthalmic lens notation, converting from plus cylinder to minus cylinder keeps the same optical effect but shifts the axis by 90 degrees. The axis marks the meridian with no cylindrical power, and switching to minus cylinder swaps which meridian carries the power, so the axis becomes perpendicular to the original.

An axis of 135 degrees is perpendicular to 45 degrees (since 135 plus or minus 90 equals 45, and axes are modulo 180). Therefore, the new axis is 45 degrees.

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