Certified Paraoptometric (CPO) Practice Exam 2025

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What distinguishes High-Index lenses from other types?

They are thicker than average
They have a higher refractive index
They are made solely from plastic
They are the least scratch-resistant

The correct answer is: They have a higher refractive index

High-Index lenses are characterized by their higher refractive index compared to standard lenses. This higher refractive index allows for the bending of light more efficiently, which means that these lenses can be made thinner and lighter for the same prescription strength. This is particularly advantageous for individuals with stronger prescriptions, as it can reduce the overall thickness of the lenses, making them more cosmetically appealing and comfortable to wear. Considering the other options, High-Index lenses are not necessarily thicker than average; in fact, they are typically thinner due to their higher refractive index. They can be made from various materials, including plastic and glass, rather than being limited to plastic. Furthermore, while High-Index lenses can be scratch-resistant, they are not inherently the least scratch-resistant option available, as advancements in lens coatings have improved the durability of various types of lenses.