Simply stated, the cornea is the front, clear, curved window of the eye.  It protects the inside of the eye, supports a healthy tear film and focuses light (along with the lens on the inside of the eye) for clear, sharp vision.

If the cornea is damaged or injured, vision will be distorted.  Many refractive surgeries like LASIK and PRK work by changing the shape of the cornea and how light focuses on the retina