I've only known one person with optic nerve hypoplasia. He was 3 years old and went to a special needs preschool, receiving OT, PT, and speech services. He also wore glasses. He was in my preschool class one summer, and he was definitely very delayed. This is just one kid though.
I definitely agree with what Callista said. Listen to your instincts, and get a second opinion. If it does turn out to be nothing, you will feel much better about all of it, and if he does need treatment, he will receive it early.
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Not all those who wander are lost... but I generally am.