Prism glasses compensate for eye misalignment by redirecting the light rays to make the two images align. Prism glasses are measured and prescribed in prism diopters. The axis must also be ...

His glass prisms not only let light pass through but also redirected it sideways into the room. ... ray II is converged by the prism refraction, and ray III is recycled by other prisms.

In other words, a prism seems only to bend (refract) light, leaving it otherwise unaltered. But it does so to different degrees (that is, at different angles) for different colors.