Cod liver oil might help. It contains vitamin A, which is good for eyes. And yes,
too much vitamin A can be bad or even kill a turtle. Once a day is good enough,
like Corey said.
I think it depends on the cause of the swollen eyes. Cod liver oil will help for
vitamin A deficiency or general discomfort, turning off the UVB will help for light
irritation. If the eyes are still swollen after you do those two, the cause is
something else. Respiratory infection (RI) can cause swollen eyes too.
If RI is suspected, you need to take your turtle to a vet quickly. Only a vet can
give you the exact dosage of the antibiotic to cure RI. Meanwhile, make sure your
water temperature is 78 F - 80 F and basking temperature about 10 F above
the water temperature. That'll bump up your turtle's metabolism that can help
combat illness. And try to get your turtle to eat, it needs the calories.
For more RI information, search the forum
Good luck!