This does not sound like a primary visual problem. It sounds like one of several possibilities.
His blood pressure could be low. When you stand up too fast, your blood pressure can drop too fast. You would see lights or tunnel vision and feel like your are going to pass out. This can happen with medications, dehydration, illness, etc.
His blood sugar could be too low also.
He could be having a migraine episode. These usually only last 15-20 minutes.
You should have his blood pressure checked. He needs to get fluids down and some sweets. If this continues, he needs to see his physician
Hope this helps and thank you.