Which type of lens has the same power and curvature in every direction?

A lens with the same power and curvature in every direction is referred to as a spherical lens. Spherical lenses have a uniform curvature across their surface, which results in equal optical power regardless of the direction of the light entering the lens. This characteristic allows them to correct for simple vision problems like nearsightedness or farsightedness.

In contrast, cylindrical lenses have different curvatures in different meridians, meaning their power varies based on the orientation. This design is specifically used to correct astigmatism, where the eye's curvature is irregular. Bifocal lenses are designed with two distinct optical powers to accommodate both near and distance vision, and prisms are utilized for altering the direction of light for conditions like strabismus. Each of these alternatives serves specialized functions and does not possess the uniform properties that define a spherical lens.