Base Curve

[majucalicut]

I have a sunglass and a lens clock with me. I want to measure the base curve of the sunglass with the lens clock in order order a rx lens from the lab in that base curve. Now my question is where should I place the lens clock? On the front surface or on the back surface of the sunglass ?

[Chris Ryser]

I have a sunglass and a lens clock with me. I want to measure the base curve of the sunglass with the lens clock in order order a rx lens from the lab in that base curve. Now my question is where should I place the lens clock? On the front surface or on the back surface of the sunglass ?

The base curve is always the front or plus surface.

[Diane]

On the front. If the sunglasses are plano, you will have the same power on each surface, however the front will be plus and the back will be minus.

Diane

[MikeAurelius]

Also, rotate the lens clock 90 degrees to ensure that you do not have a bi-toric lens front. Some manufacturers of sunglass lenses use a bi-toric design. Of course, you aren't going to get a bi-toric from your lab...

[finefocus]

A bi-toric eyeglass lens? No. If it's a plano, and it's "bi-toric", then it's really "warped".

[MikeAurelius]

Try again. Gargoyles (are they still in business?) for one, used a toric design on their sunwear. The lens was actually plano (flat) on the vertical axis with all the curve through the horizontal axis.

Perhaps bi-toric was an incorrect phrase, but it is still accurate, the Gargoyle lenses had a toric front and back surface (therefore: bi-toric).

[finefocus]

So, a flat sheet formed into a wrap-around configuration? I guess that makes a toric surface.