What is the spherical equivalent for -2.00 -1.00 X 100?

What is the spherical equivalent for -2.00 -1.00 X 100?

• A. -2.00
• B. -2.50
• C. -2.25
• D. -2.75

Answer: (B)

The spherical equivalent is found by averaging the powers in the two principal meridians of a sphero-cylindrical prescription. In this case, the power along the axis is the sphere value: -2.00. The power in the perpendicular meridian is the sphere plus the cylinder: -2.00 + (-1.00) = -3.00. Averaging these two gives (-2.00 + -3.00) / 2 = -2.50. The axis angle doesn’t affect this average, since SE summarizes the overall refractive power. So the spherical equivalent is -2.50.

The spherical equivalent is found by averaging the powers in the two principal meridians of a sphero-cylindrical prescription. In this case, the power along the axis is the sphere value: -2.00. The power in the perpendicular meridian is the sphere plus the cylinder: -2.00 + (-1.00) = -3.00. Averaging these two gives (-2.00 + -3.00) / 2 = -2.50. The axis angle doesn’t affect this average, since SE summarizes the overall refractive power. So the spherical equivalent is -2.50.