Certified Paraoptometric (CPO) Practice Exam 2025

Which lens type is inadequate for prescriptions that include cylinder?

1. Spherical lenses

2. Aspheric lenses

3. Multi-focal lenses

4. Spherocylindrical lenses

The correct answer is: Aspheric lenses

Aspheric lenses are designed to reduce distortion and improve visual acuity by providing a gradual change in curvature, which can be beneficial for individuals with certain refractive errors. However, when it comes to prescriptions that include cylinder (cylindrical power), which corrects for astigmatism, aspheric lenses may not adequately address the specific requirements of these prescriptions. Cylinder in a lens is necessary to correct for the uneven curvature of the cornea, and lenses specifically designed for such corrections, such as spherocylindrical lenses, are more appropriate because they can incorporate both spherical power and cylindrical power into the same lens, effectively addressing astigmatism. While spherical lenses and multifocal lenses can also serve various vision correction needs, their capability to handle cylindrical corrections may be limited compared to spherocylindrical lenses. This distinction highlights why aspheric lenses are seen as inadequate for prescriptions that include cylinder.