What is the spherical equivalent of -2.00+3.00x90?

To find the spherical equivalent of a prescription given in the form of cylinder notation, such as -2.00 + 3.00 x 90, the formula used involves converting the cylindrical portion into a spherical equivalent.

The spherical equivalent is calculated by taking the sphere value and adding half of the cylinder value. In this case, the sphere component is -2.00 D and the cylinder component is +3.00 D (at an axis of 90 degrees).

Calculating the spherical equivalent involves the following steps:

1. Start with the sphere component: -2.00 D.

2. Take half of the cylinder component: +3.00 D / 2 = +1.50 D.

3. Add this to the sphere value: -2.00 D + 1.50 D = -0.50 D.

Thus, the spherical equivalent for the given prescription is -0.50 sphere. This value indicates the average power needed to correct the refractive error and helps in comparing different prescriptions or in selecting appropriate lenses.