The Eye of Osiris was a gem that belonged to Demigoddess Osiris who had an ability that was strong enough to even look into the past of gods like Karyk. This was also the ability which gave her an ability to know things that others didn't, helping her take decisions accordingly.
It was said that this was also the reason Osiris was very peculiar about who she associated with. She never used her abilities to help others.
However, unlike Osiris, the gem that came into being after her death only had a fraction of her strength. Let alone being able to look through the past of gods, it couldn't even look through things directly associated with them... Things like the stone of time and the Grimoire of Necromancy. Whenever it tried, it only faced a dark cloud that stopped it.
The gem could only help someone look through ordinary items and Numens associated with Demigods.