Certified Paraoptometric (CPO) Practice Exam 2025

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Gear up for the Certified Paraoptometric (CPO) Exam 2025. Study with interactive quizzes and multiple-choice questions with comprehensive explanations. Excel in your exam with our tailored preparation tools!

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What is the purpose of the axis in a cylindrical lens?

To indicate the power of the lens
To determine the direction of the cylinder
To define the base curve of the lens
To measure the lens thickness

The correct answer is: To determine the direction of the cylinder

The purpose of the axis in a cylindrical lens is indeed to determine the direction of the cylinder. In optometry, cylindrical lenses are used to correct astigmatism, which is caused by an irregular curvature of the cornea or lens. The axis of the cylindrical lens indicates the orientation in degrees (ranging from 0° to 180°) that the cylindrical power is applied. This information is critical for the proper alignment of the lens to ensure that the corrective power addresses the specific meridian of vision that is impacted by astigmatism. Each cylindrical lens has a specific axis where its power is effective, and this axis must be accurately measured and aligned with the patient's visual axis to achieve optimal visual correction. The other options relate to different characteristics of lenses, but do not pertain directly to the primary function of the axis in a cylindrical lens.