I'm just posting this for awareness and incase it helps anyone else as I found little information out there!
My 3yo has had chronic styes on her eyes for the last year. She's also had a couple of chalazions. Much worse on one eye than the other. They are sore and we went to the GP probably 6 times and given drops, ointment, antibiotics etc, none of it helped. Eventually referred to the hospital where they did an several eye tests (with the drops).
It turns out she is long sighted in both eyes and one is worse, the one with more styes( lazy eye), and needs glasses. They think the constant straining to see, and the fact she was possibly rubbing her eye because things appeared blurry, are what caused the styes. If it wasn't for the styes, we wouldn't have known until she was say 5 and by then they say the lazy eye might have been too far gone.
We've had no concerns about her vision at all and I was fully expecting it to be caused by something else.
So if you're in the same boat, worth exploring eyesight as a cause!