How do you think disabilities,physical or mental are treated throughout the castes? Like, loosing limbs and stuff is probably common, brain damage too. But like being "born" with one less eye could possibly get a grub squished in the brood caverns right?

Unfortunately, yeah. Alternia has a policy of culling disabled individuals, so it seems pretty likely they’d be disposed towards getting rid of trolls who are going to biologically pass on disabilities to future broods.

The thing with trolls, though, is that they go through a pupation process that usually involves a complete reconstruction of the body. While I’m no biology expert, it seems likely that it’d be hard to say with certainty that a grub will retain the same mutations after pupation; a grub with two perfectly healthy eyes might come out of the cocoon with only one, and that’s where it becomes harder for the empire to regulate things.

An obstacle from there, of course, is the cavern trials; we can only presume that the trials are designed to weed out trolls who aren’t perfectly tuned for combat and survival. But the trials likely don’t have a 100% success rate.