Re: Sims 4 Glass effect?
To me it seems a normal thing. The higher settings come with extra lightning settings, which you can see in the eyes. My best guess would be the higher setting eyes look more natural in game, but in CAS there isn't anything to look at so you get these glassy effects on them.
These eyes are the vampire eyes in my game:
I don't use CC/mods so I don't know the difference with that. As that is custom content (made by another) it would be normal that the quality is different than eyes from Maxis.