Illinois Vision Certification Practice Test

What is a minus lens commonly referred to?

1. Concave lens

2. Convex lens

3. Flat lens

4. Prismatic lens

The correct answer is: Concave lens

A minus lens is commonly referred to as a concave lens. Concave lenses are thinner in the center than at the edges and are used to diverge light rays that are entering the lens. These lenses are effective for correcting myopia (nearsightedness), as they help to spread light rays outward so that they can properly focus on the retina. In contrast, a convex lens, which is thicker in the center, converges light rays and is primarily used for correcting hyperopia (farsightedness). Flat lenses do not alter the direction of light significantly and typically serve a different purpose, such as in optical glasses that do not require corrective power. Prismatic lenses do not refer to the minus lens capability but instead alter the direction of light to address issues such as binocular vision. The definition and function of each type of lens highlight why the concave lens accurately fits the description of a minus lens.