This happened to out hamster Harriet many years ago. The pics look just like yours.
Our vet who is very experienced in small animal care and has looked after ours for years examined her and she had had a bleed in to the back of the eye. Apparently this could have been caused by a jolt from a fall most likely. It gradually filled with blood then the blood gradually sank down and was like a tiny rim in the bottom of the eye eventually and then vanished. It was likely she was blind in that eye afterwards. She needed steroid drops for two weeks (maxitrol) and never seemed in any pain.
It can also be caused by high blood pressure or glaucoma which can be seen in some hybrids or lines of pure breeds but that wasn't the case with Harriet. You may want to take her make and suggest a steroid drop or a recheck though in case it is glaucoma though the eye normally swells with this and can rupture. It also needs a steroid eye drop about 4 times a day
She did have eye problems though and needed frequent eye drops with artificial tear drops but she lived a normal lifespan.
Harriet's eye problem