The cornea is the transparent structure located in the front of the eye, covering the iris, pupil, and anterior chamber. About 40 of the eye’s 60 diopters are present in the cornea. The cornea is supplied with oxygen and nutrients through tear-fluid and not through blood vessels. That also explains why the cornea is so clear. Overusing contact lenses can lead to oxygen deficiency, ultimately causing blood vessels to appear in the cornea. If the blood vessels grow to close to the middle, it can cause partial vision loss. Refractive eye surgery to correct eye disorders such as Myopia, Hyperopia, and Astigmatism (known as refractive errors), usually involves surgically reshaping the cornea using laser technology (though lasers are not always used). Examples of FDA-approved procedures are LASIK, PRK, and Epi-LASIK.