The Mythrol claims that he's still half-blind after being frozen in carbonite in The Mandalorian. Introduced in the Star Wars/Disney+ show's premiere, the unidentified Mythrol was Din Djarin's final bounty before he encountered Baby Yoda. The Mandalorian season 2, episode 4, "Chapter 12: The Siege" brought back the character where he complained about the effects of Mando's decision to keep him in carbonite.
The idea of being frozen in carbonite was introduced in The Empire Strikes Back. Darth Vader had Han Solo frozen after Lando Calrissian turned on his fellow space smuggler and his friends on Bespin. It wasn't until Return of the Jedi that the galactic runner was freed from being trapped in the solidified carbonite by Leia Organa in Jabba the Hutt's lair on Tatooine. While Han came out alive after being frozen, he didn't immediately have the capacity to function, with the character citing being unable to see.
The unnamed Mythrol in The Mandalorian also experienced the same thing when Mando froze him in carbonite in the series premiere. Following an attempt to sabotage their trip back to Nevarro where the blue alien was supposed to be delivered to Greef Karga - the Bounty Guild head at that time - Mando ensured that the rest of his mission was going to go smoothly by freezing Mythrol in carbonite and delivering him in that state. When they reunited in The Mandalorian season 2, Mythrol revealed that one of his eyes is still blind from his time being in the carbonite block. Between Han and Mythrol's experience, losing the ability to see is one of the most common effects of being carbon frozen, and this is part of the medical condition called hibernation sickness.
First mentioned in the original trilogy, hibernation sickness or carbon sickness is a medical state a creature would be in once they are taken out being suspended animation in carbonite. Temporary blindness is one of the symptoms of the condition, and so is exhaustion, weakness, dehydration, dizziness, and memory loss. While not much is known regarding this, as there are only a few instances where Star Wars reconnects with creatures frozen in carbonite, like Han and Mythrol, the loss of eyesight, in particular, could have something to do with the eyes being put under extreme external pressure. In the real world, rubbing the eyes too hard can lead to damaged cornea, and in worst cases, one would need a cornea transplant to restore their eyesight. Even when one puts steady pressure on the eyes for a brief time, vision becomes blurry and distorted. Given this, one can only imagine how much more detrimental it is if the eyes are subjected to constant and stronger pressure from being frozen in carbonite for a significant amount of time.
Eventually, Han Solo's eyesight returned after around six to eight months of being frozen in carbonite. It's unclear exactly how long it took for him to get it back, but before the Battle of Endor, he's already fully functioning again. Since The Mandalorian didn't show the Mythrol being freed from his carbonite block, it's difficult to gauge how long he was frozen for, but he was clearly traumatized by it as he's still reeling from its effects that it's safe to say that he won't be doing anything to be frozen again.