The Cornea is an extremely sensitive transparent avascular tunic located at the anterior portion of the eyeball. The cornea refracts light before the crystalline lens do. Its curvature is secondarily essential to let the eyeball focus in one point. It is directly superficial and anterior to the iris, pupil and the aqueous humor.
If you don't believe that it's sensitive, touch it and you will know why. It is sensitive because it used as a defense mechanism. Just imagine dust landing on the cornea, and you close your eyelids, but it is still there. You will feel extremely excruciating pain in the cornea that the foreign body will stay there and might go deeper. Just consult the ophthalmologist if this happens.