My daughter has been complaining about a blind spot that just showed up in one eye. She had neuritis several years ago in the same eye. The optometrist said he can't see anything wrong, but he had her do a Visual Field test and it showed that there isn't anything wrong and no blind spots. He had her see an ophthalmologist and he said nothing is wrong too. But she insists there is a loss of vision. What could be the problem here and what should be the next step to diagnosing and treating this problem?