Are the eyes swollen as well? Any other symptoms? (Open-mouth breathing, frequent yawning, bubbles from the nose or mouth, etc.?)
Is the water being kept clean? What is the temp of the basking area and water?
Are they eating OK? If so, what are you feeding them?
On the chance it could be a vitamin A deficiency (will cause the eyes to swell and close), you could gently apply some plain cod liver oil with a q-tip to the eyes 1-2 times a day for several days. (Buy some cod liver oil capsules and open them if you can't find a small bottle of it.) If it is a Vit A deficiency, it should help it.
What is your set-up like?