The cornea's the transparent front part of the eye that covers the iris, pupil, and anterior chamber. Together with the lens, the cornea refracts light, accounting for approximately two-thirds of the eye's total optical power. In humans, the refractive power of the cornea's approximately 43 dioptres. While the cornea contributes most of the eye's focusing power, its focus's fixed. The curvature of the lens, on the other hand, can be adjusted to "tune" the focus depending upon the object's dista… (More on Cornea)