What is the SE CLs Rx value given a spectacle Rx of -7.00 -1.25 x 090?

What is the SE CLs Rx value given a spectacle Rx of -7.00 -1.25 x 090?

• A. -7.00
• B. -8.25
• C. -7.50
• D. -7.25

Answer: (C)

The SE CLs Rx value is found from the spherical equivalent, which represents the average power across principal meridians for a astigmatic prescription. To get it, take the sphere and add half of the cylinder: SE = Sphere + Cylinder/2. With a spectacle Rx of -7.00 sphere and -1.25 cylinder at 90 degrees, the two principal powers are: - 180-degree meridian: -7.00 + (-1.25) = -8.25 - 90-degree meridian: -7.00 The average of these is (-8.25 + -7.00) / 2 = -7.625 D. For a CLs (contact lens) prescription, this mean power is typically rounded to the nearest standard increment available, which in the given choices corresponds to -7.50 D. So the SE CLs Rx value is about -7.50 D. The other numbers reflect either just the sphere (-7.00), the power in one meridian (-8.25), or a different mean rounding (-7.25).

The SE CLs Rx value is found from the spherical equivalent, which represents the average power across principal meridians for a astigmatic prescription. To get it, take the sphere and add half of the cylinder: SE = Sphere + Cylinder/2.

With a spectacle Rx of -7.00 sphere and -1.25 cylinder at 90 degrees, the two principal powers are:

• 180-degree meridian: -7.00 + (-1.25) = -8.25

• 90-degree meridian: -7.00

The average of these is (-8.25 + -7.00) / 2 = -7.625 D. For a CLs (contact lens) prescription, this mean power is typically rounded to the nearest standard increment available, which in the given choices corresponds to -7.50 D.

So the SE CLs Rx value is about -7.50 D. The other numbers reflect either just the sphere (-7.00), the power in one meridian (-8.25), or a different mean rounding (-7.25).