There are multiple causes of vision loss, and multiple diseases of the eye can attack and manifest as vision loss. The vision loss caused by brain tumor has two characteristics: 1. Slowly, because it is the vision loss caused by tumor compression, so as the tumor gradually increases, the vision only slowly decreases to a more and more serious degree; 2. One side of the vision loss, the other side is normal, that is, the visual field defect, the manifestation in life is that when looking straight ahead, both eyes have afterglow on both sides will see the range. If there is a visual field defect will be found when looking straight ahead, the right or left side can not be seen. This happens when walking on the street, often bumping shoulders with others, because normally there is afterglow and can pass when brushing shoulders with pedestrians, while the patient can’t do it and will definitely collide with others. The afterglow on both sides of the face is narrowed, and when you look at something, you will find a dark, blocking area on the upper left, lower left, upper right or lower right.