What do retained eye caps look like?

[Bogertophis]

Can this also be done if you have to clean them if they ever slither across a turd? ...

Of course. Retained eye caps can also just look very cloudy (milky) as if not shed. But if in doubt, have them checked & removed by an experienced vet (like if the above gentle methods don't work) as you can permanently damage eyes & cause blindness if too "aggressive". This has happened before, owners not knowing when to stop, etc. Get a herp vet involved like if you ever adopt a snake that has several stuck layered eye caps, or if in doubt...better safe than sorry. If you damage the eyes, they can also get infected.