American Board of Opticianry (ABO) Practice Test 2025 - Free ABO Practice Questions and Study Guide

To determine the total power of the prescription +2.00 -2.00 x 090, we need to analyze it as a combination of a spherical and a cylindrical component. The prescription includes a sphere of +2.00 diopters and a cylinder of -2.00 diopters with an axis of 090 degrees.

The spherical component provides the primary refractive power of +2.00 diopters, while the cylindrical component represents a correction for astigmatism, which is -2.00 diopters. The total power in a cylindrical prescription is calculated using the formula:

Total Power = Sphere + Cylinder

In this case, we can look at the impact of the cylinder. Since cylindrical power is also affected by the axis where it is placed, when aligned in a specific orientation (like at 90 degrees in this case), the -2.00 diopter cylindrical power serves to neutralize some of the spherical power when viewed along its axis.

However, for the total power when the cylinder and sphere are combined, it's crucial to remember that the spherical power remains +2.00 diopters when evaluating along its own axis. The cylinder does not add power directly in all meridians; instead, it modifies how the light is