What will be the result of decentering a plus lens upward?

Decentering a plus lens upward results in the creation of a base up prism effect. This phenomenon occurs due to the optical properties of convex lenses, which are used to converge light. When a plus lens is decentered upward, the optical center of the lens moves lower than the point where the light rays converge, causing the light to bend more in the upward direction at the periphery of the lens.

The effect can be visualized by realizing that as light passes through the lens, it is refracted towards the base of the prism formed by the lens due to the upward decentering. Consequently, the top portion of the lens acts as the base while the bottom part acts as the apex of the prism, leading to the perception of a base up prism. This principle is crucial in understanding adjustments needed in optical prescriptions, particularly in cases involving prism corrections for vision alignment issues.