I see this all the time on parrots. It makes them look sleepy....lol. From what I have observed in parrot tanks containing dozens and hundreds of parrots I would say, on average, about one out of every 15 have these sleepy looking eyes. I too think it looks cool. No idea if it impacts their vision.
Interesting ?My BP had eyes like that but as he grew they became normal.
He sees just as well as my other parrots.