How Did Palermo Lose His Eye?

During the heist, he was shot at by Gandía and he ended up needing surgery to get shards of glass removed from his eyes. He spent the rest of the heist wearing an eye patch.

Is Palermo blind?

Palermo, the commander in charge, is temporarily blinded in the struggle, but retains command after Nairobi removes glass shrapnel from his eyes, and the guards restrained.

Why is Palermo helped Gandia?

So, in Episode 3, "Lección de anatomía"/"Anatomy Lesson," Palermo essentially helps Gandia escape, coaching him through the process of breaking his thumb so that he could slip his hand through the handcuffs binding him.