A good supply of healthy blood is needed for healing. The cornea doesn’t have blood vessels as most other tissues. If they did, the cornea wouldn’t be clear. A good blood supply allows the bodies defense mechanisms to “attack” an invading bacteria or fungus, but since the cornea doesn’t have a blood supply, it is vulnerable to infections that get out of control. While the body will begin to grow blood vessels in an attempt to repair itself, this is a slow process and much too slow to do much good in beating back an infection.