Incremental damage to the eyesight. The damage to the vision (at first) might be so minimal that it may not even come to the conscious notice of the patient. Even if it does, the patient is unlikely to link it to a brain tumor. Often, the damage occurs incrementally over time, eluding the patient’s notice until it is so pronounced that the patient has difficulty in navigating around obstacles as they walk, or suffers successive accidents while driving. Such vision loss generally tends to be pronounced in one eye. The medical term for such visual impairment, especially peripheral, is bi-temporal hemianopsia.