with basic lubricating eye drops from the drug store, the best thing to do is have the patient in your lap, with their butt pressed up against your body, then squeeze the bottle so the drops flush over the closed eye, let go and the rat will open their eyes, to glare furiously at you, and the drops get into the eye. If you are just wiping the porphyrin from the eye, you can use a damp cloth or paper towel.
IF that eye starts to squint or look full around the lids compared to the other one, you have a nakie who could have eye issues (often only 1 eye will be "defective") and you might need to change your carefresh to fleece only to prevent the paper from getting stuck under the eyelids. I can dig up a pic if you want to see what I mean by "full" eyelids?