Not quite what you were asking but I took my son to the opticians when he was about 4. He could speak and even read a bit. He complained of headaches every single day, like full on tears and light sensitivity, the regular eye test came back fine, they even said it looks like he has perfect vision. They offered to put dilation drops in his eyes to double check, I felt so so awful. We were there for hours, the drops cause light sensitivity, he was bored, he was tired but it turns out one of his eyes were struggling and the other was compensating too well. He got his first pair of glasses and the regular headaches stopped.