What is the total optical power in the vertical meridian?

• A. -1.00
• B. -2.00
• C. -1.25
• D. -1.50

Answer: (A)

The key idea is how cylinder power works in different meridians. In a sph/cyl prescription, the cylinder adds power only in meridians perpendicular to the axis; the meridian along the axis itself has no cylinder power.

So, to get the vertical meridian power, you need to know whether the vertical direction is the axis or perpendicular to it. If the axis is vertical, the vertical meridian is the axis meridian and has no cylinder effect, so its total power equals the sphere value. If the axis were horizontal, the vertical meridian would be 90 degrees from the axis, and its power would be sphere plus cylinder.

In this case, the vertical meridian power being -1.00 means the vertical direction is the axis direction, so the vertical meridian carries only the sphere value, -1.00. The other options would require the cylinder power to contribute in the vertical meridian, which would occur if the axis were not vertical.