If a patient is prescribed a -12.00D spherical lens and the lens is moved closer to their eyes, what will happen to the effective power?

When a -12.00D spherical lens is moved closer to a patient's eyes, the effective power of the lens increases in terms of its minus power. This occurs due to the optics of lenses and how they function based on their position relative to the eye.

In simple terms, moving a concave lens (like the -12.00D lens) closer to the focal point of the eye increases the convergence of light rays that enter the eye, which effectively intensifies the lens's ability to diverge light. This results in a higher effective dioptric power because the shorter the distance from the lens to the eye, the greater the optical effect on the incoming light rays.

For a patient with a high degree of myopia, like -12.00D, this change can significantly enhance the lens's ability to correct their vision within the range of their prescription, leading to improved clarity when objects are viewed at various distances. Thus, the overall effective power is higher than initially prescribed due to the closer positioning of the lens to the eye.