Many feral cats and kittens come to me with eye infections, normally caused by Feline Herpesvirus or Feline Calicivirus. The vet often prescribes some antibiotic eye drops for them.
Here is a video I made with Mickey, a feral kitten, cleaning his eyes and administering the eye drops Eye Drops
In the video, I also cleaned his eyes as he had a lot of gunk around them. To do this I got a damp cotton pad and gently wiped his eyes. I then administered the drops by gently opening his eye and squeezing one drop to each eye.