If a lens is decentered by 5mm, how much prism is induced with the RX -3.50 -1.00 x090?

To determine the amount of prism induced by a decentered lens, we apply the formula for calculating prism in diopters, which is given by:

Prism (in diopters) = Decentration (in mm) x Refractive Power (in diopters) / 1000.

In this case, the refractive power of the lens can be determined by analyzing the prescription, which is given as -3.50 -1.00 x 090. When considering decentration, the relevant power is the spherical equivalent.

The spherical equivalent is calculated as:

-3.50 + (–1.00 / 2) = -3.50 - 0.50 = -4.00 D.

Now, we have a decentration of 5 mm. Plugging the values into the prism formula:

Prism (in diopters) = 5 mm x -4.00 D / 1000 = -0.02 D.

To convert this to prism diopters, we recognize that 1 diopter equals 1 prism diopter at 1 meter, and convert -0.02 D to prism using the equivalency that 1 degree of prism is caused by 1 diopter at