One crusty eye

My four year old mama cat had kittens a month ago and has since developed an issue with one eye. Her eye itself seems fine, but the inside corner is swollen and gets dark crusties. She has no other discharge, nor does the eye seem red. I applied salt water every day and it seemed to clear up but when I stopped it immediately came back. It doesn't seem to hurt when I clean the area, nor does she have a loss of appetite or weight. Is there something more effective than the salt water I should try? Is it just a clogged tear duct? Any info would be greatly appreciated.