Some (all?) frogs have a transparent eyelid that covers the eye and I am suspicious that there is an infection that is preventing this from opening. I had a tree frog with this and I couldn't seem to find the right medication (and it died). Perhaps someone with the right info will come along here or you could try posting to "Talk to the Frog" which is another source or search on google for frog infections. I would definitely say this is something to be concerned about. Contact a Vet if you have one near enough that knows something about frogs and you can afford it. They can provide an antibiotic.