[pbhjpbhj]

I'd guess pain receptors == ability to locate and limit damage.

With leprosy, sufferers lack the ability to feel when they've injured themselves, they end up tearing the flesh off their limbs and breaking the feet down to a pulp through accidents as they can't tell they've injured themselves.

If you don't feel the piece of sand in your eye, then you're going to carry on damaging the eye until you do feel it. At which point, with minimal pain receptors the eye is likely damaged beyond recovery.

I had a scratched cornea recently, the scratch enabled an infection to take hold very rapidly.