The ivermectin will treat worms & parasites but will not help with the swollen eye,, I suggest you use an antibiotic such as tylan 200 or Baytril. Tylan can be purchased at most good farm type stores or ordered from a supply store like Cutler supply or Smiths or Jeffers. The Baytril will have to come from a vet. If not treated soon it will develop into a hard mass under the eyes.. The worst thing is they can not see and will starve as this will stay for a very long time unless it is cut out. This is not always fatal if you keep after it and attend to it often with an antibiotic. But need to be treated quickly ,,,,,,,,, connerhills