Certified Paraoptometric (CPO) Practice Exam 2025

What is characteristic of planocylindrical lenses?

1. They have no power across the entire lens

2. They have power in all areas

3. They are designed specifically for reading

4. They correct astigmatism

The correct answer is: They correct astigmatism

Planocylindrical lenses are specifically designed to correct astigmatism, which is a common refractive error caused by an irregular shape of the cornea or lens. These lenses have one meridian that is plano, meaning it has no refractive power, and another meridian that has cylindrical power to effectively bend light in a specific direction. This unique design allows them to address the varying degrees of curvature in the eye, aiding individuals who experience blurred vision due to astigmatism. The other options do not accurately describe planocylindrical lenses. For instance, while some lenses may not have power across their entire area, this characteristic does not apply to planocylindrical lenses since they do have cylindrical power in one meridian. Similarly, stating that they have power in all areas does not correctly convey their specific function, which is limited to the astigmatic correction. Furthermore, while they may assist in visual correction at different distances, they are not designed exclusively for reading, which would be more typical of reading or bifocal lenses.