What is the spherical equivalence of the Rx -2.75 -1.00 x 180?

To determine the spherical equivalence of a refractive error expressed in prescription format, one must understand how to convert the given prescription into its spherical equivalent.

In the prescription -2.75 -1.00 x 180, the first part, -2.75, refers to the sphere power, which is the main refractive error. The second part, -1.00, is the cylinder power, and x 180 indicates the axis of the cylinder.

The formula for calculating the spherical equivalent is as follows:

Spherical Equivalent = Sphere + (Cylinder / 2)

For this specific prescription:

• Sphere = -2.75

• Cylinder = -1.00

Now, by substituting the values into the formula:

Spherical Equivalent = -2.75 + (-1.00 / 2)

= -2.75 + (-0.50)

= -3.25

This calculation shows that the spherical equivalent of the prescription is -3.25. Therefore, the correct choice aligns with this computed value, confirming that the spherical equivalent accurately reflects the combined refractive error presented in the prescription format.