ABO (American Board of Opticianry) Practice Test

A lens with a front curve of +6.50 requires a back curve of -7.50 in order to have a corrective power of -1.00. This is because the front curve is positive, indicating that the lens is convex, while the back curve is negative, indicating that the lens is concave. This combination balances out to create the desired corrective power of -1.00. The other options, -6.50, -2.00, and -1.00, do not match the required back curve for this specific front curve. -6.50 is the same as the front curve, making the total power 0, while -2.00 and -1.00 would result in a lens power that is too weak or too strong, respectively. It is important to pay attention to the signs of the front and back curves when determining the correct lens power.