The cornea is the clear, round, "window" of tissue that allows light to enter the front of the eye. If the cornea becomes severely diseased or damaged, it can distort or even block the normal path of light into the eye. When this happens, light does not focus normally on the retina, the layer at the back of the eye that is responsible for sight. As a result, there can be a significant loss of vision in the affected eye.
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