The covering of our eyes called the cornea is an incredible example of complex design. The material of which the cornea is made has to be perfectly clear to allow light to pass through it so that we can see. It is exposed to the air with all of the bad things air contains--pollen, dust, chemicals, etc. It has to be able to withstand blows and fit to a curving surface full of a fluid which maintains the pressure of the eye.
Recently we received a note from Marty Gilliam, a mechanical engineer from Athens, Alabama, about how the cornea is designed so that, if it gets scratched, it can heal without obstructing our vision. A quote from his letter:
If you cut your skin, the cut heals from the bottom up, thereby scar tissue is formed. Not so with the eye. When the cornea experiences a scratch, the cells of the separated walls move toward one another, and close the scratch or cut, therefore no scar tissue is formed. If scar tissue formed every time we scratched our corneas, by the time we were middle-aged we would be looking through many cloudy lines. Another dandy design from the Designer!