In a minus cylinder prescription with axis at 90 degrees, the cylinder power is applied to which meridian?

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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 a minus cylinder prescription with axis at 90 degrees, the cylinder power is applied to which meridian?

Explanation:
The cylinder power sits on the meridian perpendicular to the axis. The axis is the meridian with zero cylinder power, so the cylinder effect shows up 90 degrees away. If the axis is at 90 degrees, the cylinder power is applied to the 180-degree meridian (the horizontal line). That’s why the 180-degree meridian carries the cylinder term, while the 90-degree meridian has only the sphere power. For example, with a minus cylinder at axis 90, the power along 180 degrees is the combination of sphere plus cylinder, while along 90 degrees it remains the base sphere.

The cylinder power sits on the meridian perpendicular to the axis. The axis is the meridian with zero cylinder power, so the cylinder effect shows up 90 degrees away.

If the axis is at 90 degrees, the cylinder power is applied to the 180-degree meridian (the horizontal line). That’s why the 180-degree meridian carries the cylinder term, while the 90-degree meridian has only the sphere power. For example, with a minus cylinder at axis 90, the power along 180 degrees is the combination of sphere plus cylinder, while along 90 degrees it remains the base sphere.

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