The “best form” or "corrected curve" shape of a lens is one that provides as close to the the same vision at center and in the periphery as possible, as the eye moves normally behind the lens. For finished lenses, manufacturers choose both front and back curves; for semi-finished lenses, a recommended series of front curves are provided usually in a base curve chart.

When you order lenses from the lab, they already have these charts loaded in their computer lab management systems so the correct base curve is chosen for your order. For the best vision in a lens, it’s better to let the lab choose the base curve. In best form lenses, the front surface curve is spherical i.e., the same curve or radius in all directions from center.