In the notation +2.00 -0.50 X180, what does the 180 represent?

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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

In the notation +2.00 -0.50 X180, what does the 180 represent?

Explanation:
The number after the X is the axis orientation of the cylindrical correction. It tells you the meridian along which there is no cylinder power. In this case, 180 means the axis is horizontal. The cylinder power of -0.50 is applied in the meridians perpendicular to that axis (the 90-degree meridian), so the power along 180° is +2.00 (sphere only), while the power along 90° becomes +2.00 plus the cylinder: +1.50. So the 180 is describing the orientation of astigmatism correction, not the amount of power itself.

The number after the X is the axis orientation of the cylindrical correction. It tells you the meridian along which there is no cylinder power. In this case, 180 means the axis is horizontal. The cylinder power of -0.50 is applied in the meridians perpendicular to that axis (the 90-degree meridian), so the power along 180° is +2.00 (sphere only), while the power along 90° becomes +2.00 plus the cylinder: +1.50. So the 180 is describing the orientation of astigmatism correction, not the amount of power itself.

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