I'm gonna say it: it's aemond's own fault he lost his eye in both the show and the book. Both times, he snuck out to claim vhagar. In the show, he wasn't stopped. In the book, three year old Joffrey Velaryon was with his dragon because he was an early riser and told Aemond to stay away from Vhagar, so Aemond - who was much older - pushed little three year old Joffrey over and, in his fear of being caught because he knew he was doing something his parents would like, claimed Vhagar and flew her for the first time.
Baby Joffrey, all of three years old, then of course runs to get his big brothers, likely crying and terrified. Because he's, y'know, A BABY.
In the show, Aemond claims Vhagar and with arrogance and smugness returns to the castle, high on the fact that he'd just claimed Vhagar, uncaring of how rude/insulting it may have been to claim Vhagar on the night of her previous riders funeral, like A NORMAL PERSON.
When, in the show, Rhaena and Baela confront Aemond with Luke and Jace, they're clearly upset. Their mother has just died, its her funeral, and their last tether to her - Vhagar - has been claimed by Aemond. They say he stole her, and while dragons can't be stolen, he did use underhanded tactics to obtain her and bond with her. And his haughtiness afterwards, towards the daughters of the woman whose dragon he just claimed, is what makes the altercation his fault.
Baela, upset: Vhagar is my mother's dragon!
Aemond, uncaring: Your mother is dead, and Vhagar has a new rider now.
Rhaena: she was mine to claim!
Aemond: then you should have claimed her. Maybe your cousins can find you a pig to ride. It would suit you.
Rhaena then hits Aemond, provoked into this by his cruel words and actions. Was it right? No. But it's literally the night of her mums funeral, Vhagar has been claimed by someone who clearly doesn't care about her mother, and he just insulted her. Aemond pushes Rhaena to the ground, so Baela slaps him in defense of her sister, and he punches her in the face.
Aemond: come at me again and I'll feed you to my dragon!
Now aemond is threatening to murder his cousins, which is par for the course for hid character. He always had kinslaying in him.
The fight devolves even more, and Jace and Luke get involved, defending their cousins. Luke, a little kid, is whacked and shoved to the ground, so Jace jumps in. Then Baela decides to help, and she and Luke - both of them younger and smaller - start wailing on Aemond (u go kids).
Aemond kicks Luke off of him, throws Baela off, and stands only to grab Luke - only five - by the throat and hold a rock over his head and threaten him.
Aemond: you will die screaming in flames just as your father did, bastard.
Luke, terrified and upset: my father is still alive!
Aemond, amused: he doesn't know, does he? Lord Strong.
This is when Jace pulls his knife, literally the size of my thumb, and attacks. Jace us quickly unarmed by Aemond, who is still holding the rock, and Luke sees the blade. Aemond holds the rock over them, smirks at Rhaena and Baela, then gets sand thrown in his face and Luke slashes at him wildly, not even aiming for his eye, just aiming to stop Aemond from hurting Jace and himself and his cousins, because at this point Luke has heard death threats, and seen Aemond take on him and the other three easily and win, so of bloody course this terrified little boy used a weapon to defend himself when it became necessary.
After, Alicent makes the situation about her because she's a poor uwu baby (gag me with a chainsaw, I loathe her) and attacks Rhaenyra as though Rhaenyra and her kids were in the wrong? Gurl.
Aemond will then go on to use him losing his eye as an excuse to use his war dragon to chase fourteen year old Luke on tiny baby Arrax and have the FUCKING AUDACITY to look shocked when it went wrong? Aemond is still at fault for Luke's death even if "he didn't mean it" or "he lost control" (he's not a true dragon lmfao)
In the book, Joffrey - who is three - returns with Jace and Luke, who grabbed wooden swords - they won't help against Vhagar bbys - in defense of their brother.
Despite it being three on one, Aemond was winning the fight until Luke slashed him, and good thing he did otherwise Aemond wouldn't have stopped in my opinion. He'd have kept going, beating the boys to bloody pulps. It was stable-boys who had to end the fight, where were the guards? Cole was probably simping over alicunt tbh.
Also, Alicent was the first to demand Luke's eye in recompense for Aemond losing his soz not soz ya uwu Queen is a cunt heh
Aemond will then, years later, attack Luke because of this and kill him and start the Dance of Dragons in full because not only did he cause the events that took his eye, but also the worst war in history, all because he's a little bitch baby sociopath with genocidal tendencies lmfao
Also, Aemond got off lightly, merely losing his eye - do u know what the punishment is for people who attack a princes' daughters and the heir to the throne sons? Calling them bastards, which is treason!!!! Death. Bitch shit should be exuberant that he merely lost an eye. Unfortunately viserys is a bitch and didn't send Aemond to the Wall like Jaehaerys would have for fucking real lol