My rat has had a very similar thing since she was born. First thread I made when I got here was about it. I’m pretty sure at least with my rat it’s just a birth defect. She closes her eye partly a lot and has porphyrin around her eye sometimes. Keep an eye on her though. If you want to check out my thread for answers sooner then it called “what is wrong with my rats eye” for me it’s in the recommended reading.