Baby born too early can not see after three months

Patient: My baby was born in week 33, she was very healthy and strong so we could take her home quite fast.We are a few months short of her being 3 months old.I already have 2 children, making her the third.The question is, she still can’t see (or at least doesn’t give any indication that she does). Both my other children could see after about a month, month and a half.Is this normal for a baby born early or should I be worried?(Actually I am already otherwise I wouldn’t be asking the question…)