One sided blisters over the eye lids are quiet common findings in the mornings after sleep Common causes include insect bite, rubbing etc.... It might also cause mild swelling as the tissue around the eye has very loose connective tissue. It might be accociated with itching occasionally for which you might require mild oral antiallergic such as cetrizine generally it subsides by its own in a day or two. If the blister you mean is inside the eye (conjunctiva) you would require antibiotic eye drops thrice a day for a week to combat superadded infection. hope this helps :)