Convex lens: A convex lens is thicker in the center and thinner at the edges. For patients with myopia, a convex lens can cause the light to diverge outward after passing through the lens, causing the focus of the light entering the eye to move backward, thereby focusing on nearby objects.

Concave lens: A concave lens is thinner in the center and thicker at the edges. For patients with hyperopia, a concave lens can make the light converge inward after passing through the lens, so that the focus of the light entering the eye moves forward, thereby focusing on distant objects.

Selection of glasses power: Power is a unit used to describe the ability of glasses lenses to refract light. The required power for myopic patients is a negative value, and the required power for a hyperopic patient is a positive value. The choice of spectacle power should be determined based on the doctor's advice and eye examination results to ensure accurate vision correction.