Eyewear Base Curve Data

I have been doing some research into eye wear and came across the Base Curve specification. For those interested - the base curve corresponds to the degree of curvature of a pair of glasses or sunglasses.

Glasses with a lower base curve, say… 6.5 are relatively flat. Glasses with a high base curve 9+ are more of the “wrap-around” style.

I’m wondering if anyone knows of a source of data that specifically provides the dimensions / curvature associated with the most common base curves.

For a pretty good graphical explanation of base curves check out the image from the SpyOptic site below.

the base curve corresponds to the degree of curvature of a pair of glasses or sunglasses.

Optically, base curve actually pertains to the curvature of the lens, not the frames. It can, of course, apply to anything with a curvature to it, like the frames themselves.

The base curve on contact lens is applied to the inside surface of the lens; the spherical surface that touches the cornea; typical radius values range from 8-10mm. On spectacles, it is applied to the exterior surface of the lens.

With regard to the frames, these folks are apparently adapting this term to describe the cylindrical plane of the face. What it’s value might be is hard to say; inches appear to be too large (a radius of 6-9 inches would be too big). Millimeters are obviously too small. Centimeters, maybe; 6-9cm. (?)

The “diameter” / width of the human head, might be found in Humanscale 1/2/3: The Measure of Man, by Niels Diffrient/Henry Dreyfuss Associates. Out of print for some time now but there might be a copy in your university technical library. I have an ancient copy down at the shop I’ll check this afternoon and pass on anything I find.


Hi van_ID or Lmo,

Did you guys ever find out about the relations between base curves and specific dimensions?
I was trying to find out the relation for few days but I wasn’t successful.

Do you think base curve number came has some correlation to optical diopter unit, which is dio = 1/f. (f=focal length)
and 1/f = (n-1) (1/R) so… dio=(n-1)(1/r) (where n is refractive index of the lens)???