What is the difference between spherical and aspherical contact lenses?
Aspherical lenses are also used to improve the optical quality of an image by focusing the image at a single plane. With a spherical lens, light passing through the edge of the lens doesn’t share the same focal plane as the one for light passing through the center of the lens. This is because spherical lenses tend to reflect light more strongly at the edges than in the lens center, thus focusing light in different planes. The effect is more pronounced the more area of the lens that is used such as in low light conditions when the iris aperture is much larger. This focusing error is known as “spherical aberration”. Aspherical lenses correct this optical defect: by constructing the lens with different lens radii (a spherical lens has only one radius r or curvature) thus alleviating the stronger bending of light at the edges.
