Certified Ophthalmic Assistant Practice Exam

A lens consisting of two cylinders of equal but opposite powers is referred to as a cross cylinder. This type of lens is commonly used in ophthalmic practice to refine the axis of astigmatism correction. A cross cylinder helps the ophthalmic assistant to determine the exact axis of astigmatism and fine-tune the prescription for the patient.

The other options can be explained as follows:

B. A bifocal lens is a lens with two distinct optical powers to correct both near and distance vision.

C. A converging lens is a lens that converges light rays to a focal point, used in cases of hyperopia or farsightedness.

D. A dispersion lens is a lens that separates light into its component colors, commonly used in prism correction.