In the fast paced and thrilling world of optics, the base curve is one of the three fundamental measurements of a lens, the others being index of refraction and back curve.

The base curve is the curvature, in diopters, of the front of the lens. Take a look at your glasses. If you are severely myopic, the base curve is probably zero. If you have near-normal vision, and your glasses were made to industry standard, the base curve is probably six.

Rarely, in extreme cases, the base curve is a minus. These are used for biconcave lenses, typically only seen in prescriptions of -12 or higher.Higher, of course, being a higher number after the minus sign, which is actually a lower number. This is the difference between math and jargon.