Certified Ophthalmic Assistant Practice Exam

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Study for the Certified Ophthalmic Assistant Exam. Access multiple choice questions that reflect actual exam content and receive hints and explanations for each question. Prepare effectively and embark on your path to certification!

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A lens consisting of two cylinders of equal but opposite powers is known as what?

Cylindrical lens
Cross cylinder
Convex lens
Biconcave lens

The correct answer is: Cross cylinder

A lens that consists of two cylinders with equal but opposite powers is known as a cross cylinder. This type of lens is utilized primarily in refraction testing and astigmatism correction because it can help determine the astigmatic power needed by introducing a specific amount of cylindrical correction across two different meridians. The term "cross cylinder" accurately describes the two cylindrical components that meet at a right angle, allowing ophthalmologists to assess visual acuity and refine prescriptions effectively. This distinguishes it from cylindrical lenses that have just a single cylindrical power, and from convex or biconcave lenses, which are designed for other refractive purposes without the specific dual meridian focus characteristic of a cross cylinder.