My suggestion - find an emergency vet asap!!!! With an open wound over the anus it needs to be seen by a vet as soon as possible.
Do not try to force open the kitten's eye! It will open when ready.
If the kitten was being looked after by the mother the mother would lick the anus area to aid the kitten to relieve itself. Seeing as that is not happening use a slightly rough, dampened clean washcloth. What are you feeding it? Human milk is not good for the kitten. There is replacement cat milk available at good pet stores. I am not talking the stuff you can buy at grocery stores. I am talking replacement cat milk. Very important you have the right stuff.
There must be some reason the mom left it.
It needs to get to the vet. I can not stress this enough.
Assumptions do nothing but make an ass out of u and me.
We can stick our heads in the sand for only so long before it starts choking us. Face it folks. The pet population is bad ALL OVER THE WORLD!