A rigid lens of 45.00D/-4.00 provides 20/20 vision. What power would be needed if the base curve is changed to 45.50D?

To determine the new power required when changing the base curve of a rigid contact lens, one must understand the relationship between the base curve, lens power, and the overall optical effect.

In this scenario, you started with a lens that has a base curve of 45.00D that provides 20/20 vision at a certain power of -4.00D. When the base curve is increased to 45.50D, the effective optical power of the lens changes. Generally, when the base curve is steeper, it leads to an increase in the lens's plus power or a decrease in the absolute value of the minus power needed to maintain the same effective optical correction.

The relationship can often be approximated by using the formula relating power changes to base curve changes, which indicates that for every increase of 0.50D in the base curve, the power requires adjustment. Specifically, a change of +0.50D in the base curve would mean you'd decrease the power by about 0.50D. Since the original power was -4.00D, an increase by 0.50D in the base curve leads to a new power of -4.50D; hence, the correct adjustment for maintaining equivalent