What would be the true power change if a lens with a -2.00D power receives a -1.00D cylinder?

To understand the true power change when a lens with a -2.00D spherical power receives a -1.00D cylindrical power, it's essential to first clarify how spherical and cylindrical powers work together to form the total power of a lens.

The spherical power indicates the overall power of a lens used to correct for myopia or hyperopia. On the other hand, cylindrical power corrects for astigmatism and is considered a separate component. When a cylinder is introduced to a lens, it adds to the total power of the lens in a way that the cylindrical power is effectively considered additive to the spherical power.

In this case, the starting power is -2.00D (the spherical component). Adding the -1.00D from the cylinder involves simply summing these values because they both have the same refractive effect, albeit in different orientations. Hence, we combine them as follows:

-2.00D (spherical) + (-1.00D) (cylinder) results in a total power of -3.00D.

This calculation demonstrates that when you introduce a -1.00D cylinder to a -2.00D lens, the true power change indeed results in a total of -3.00