Before revision: Summary correction power is measured in diopters by convention, an axis of 90° is vertical, 0° or 180° are horizontal if the cylinder power is positive, the lens is most convergent 90° from the axis if the cylinder power is negative, the lens is most divergent 90° from the axis if the cylinder power is zero, the lens is spherical and has the same power in every meridian Sample prescription A prescription of −1.00 +0.25 x 180 describes a lens that has a horizontal power of −1.00 D and a vertical power of −0.75 D. Only ophthalmologist write prescriptions in + cylinder.
After revision: Summary correction power is measured in diopters by convention, an axis of 90° is vertical, 0° or 180° are horizontal if the cylinder power is positive, the lens is most convergent 90° from the axis if the cylinder power is negative, the lens is most divergent 90° from the axis if the cylinder power is zero, the lens is spherical and has the same power in every meridian Sample prescription A prescription of −1.00 +0.25 x 180 describes a lens that has a horizontal power of −1.00 D and a vertical power of −0.75 D. Only ophthalmologists write prescriptions in + cylinder.