Aww how sad. I'm sorry you had that happen, but you did the right thing. At least they had mercy and care from you for the important part of their lives.
I'd suspect it's an injury until there are other symptoms. Note that because the chick is missing vision in one eye, he will be naturally depressed.
I agree with the posts about cleaning the eye with sterile eye wash or saline (not red-out drops) and then, if possible, using Terramycin...