What are the three primary types of lenses used in eyewear?

The correct answer identifies the three primary types of lenses as convex, concave, and cylindrical. Each of these lens types serves a specific purpose in vision correction.

Convex lenses are thicker in the center and thinner at the edges. They are used to correct hyperopia, or farsightedness, by converging light rays to help the eye focus on near objects more effectively.

Concave lenses, on the other hand, are thinner in the center and thicker at the edges. They are utilized for correcting myopia, or nearsightedness, by diverging light rays so that the eye can focus on distant objects properly.

Cylindrical lenses correct astigmatism, which is caused by an irregularly shaped cornea. These lenses have different powers in different meridians, allowing for proper focus in varying planes.

This instrumental classification of lenses addresses the different optical needs people have based on their vision conditions, making the identification of convex, concave, and cylindrical lenses foundational in the field of optometry and eyewear dispensation. Other options provide different categorizations of lenses but not the three primary types commonly recognized in practice.