Vogel's Rule

[melcas]

My friends I try to use this formula but I can't undestand how work. Can you explain me?

Thanks you

[Darryl Meister]

It's just a rule-of-thumb for predicting base curves:

For plus powers:

Base = Sphere Power + 6.00

For minus powers:

Base = Sphere power / 2 + 6.00

If you have a -6.00 Rx, for instance, the Base curve would be:

Base = -6.00 / 2 + 6.00 = +3.00

You should probably use 5.00 instead of 6.00 though, since base curves are generally flatter. If the prescription has cylinder power, add half of it to the sphere power first. Keep in mind that this is just a rule-of-thumb, and you should generally the manufacturer's recommended base curves.