Certified Paraoptometric Practice Test 2025 – 400 Free Practice Questions to Pass the Exam

Question: 1 / 400

Why may a contact lens prescription differ from a spectacle prescription?

For visual field testing

To use perimetry

Because of the vertex distance between contact lens and spectacle lens

Contact lenses sit directly on the eye's cornea, while eyeglasses are positioned about 12 mm in front of the eyes. This distance is called the vertex distance. The prescription for contact lenses needs to account for this difference in vertex distance, as it affects the power of the lens needed to correct the vision properly. This is why a contact lens prescription may differ from a spectacle prescription.

Options A, B, and D are incorrect because they do not directly relate to the reason why a contact lens prescription may differ from a spectacle prescription.

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The area of the space visible to the eye

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