It's important for your prescription sunglasses to have a base curve Measurement.

According to optical theory, the base curve is the curve from which all other curves are measured.

The curves that create the actual lens power are placed on the back of the lens and have a different shape.

Matching a base curve to a prescription is part of the surface.The curves needed to match a prescription are created by grinding away at the plastic on the lens.The day-to-day work of an eye doctor is no longer done at the store but at a lab.

You will learn about free-form lens design in an upcoming lesson.The base curve on a lens can only be determined by a computer.Most labs will not allow you to change or request a base curve.

I want you to know that Younger has a series of progressive lenses with variable base curve designs.The nominal lens formula or simple base curve calculations are completely ignored.

Attempting to change the lens base curve would be against the law.You can ignore them and have the job done at a good lab with a high-end edger if you smile and nod your head.Many poor frame and Rx matching problems can be overcome by a good edger.In course 3, all about frames, how to match lens and frame curves is covered.

You will need to know about base curve theory if you want to take any practical exams.

The methods below work on the spherical equivalent of the prescription.The spherical equivalent of any Rx is determined using a formula.

The cylinder power was added to the Rx sphere power.You work with the -2.50 if the Rx is a sphere.Spherical equivalents are used in contact lens work.

The most basic rule is that you always want the base curve to be as close to +6.00 as you can get.The best possible combination of curves should always be given by +6.00.

You can study the chart.The base curve will become higher if the power is higher.The base curve will become lower if the power is less than power.A base curve of + 0.25 is possible for a high minus Rx.

The spherical equivalent of the Rx is +4.00, which is the correct base curve.

The spherical equivalent of that Rx is -2.50, which is 1/2 of the base curve.

A base curve chart is a common method.Make sure you read it correctly.You must be careful when selecting a curve because the charts have overlaps and you need to be sure you are choosing the curve that is closest to that.