Glaucoma is the second most treatable blinding eye disease in the world. As an important cause of irreversible blindness, its prevention and treatment has become an important public health issue, and its ranking among the world’s leading blindness-causing eye diseases continues to climb. It is expected that by 2020, 79.6 million people worldwide will have glaucoma, 11.2 million of whom may eventually develop double vision. Glaucoma is a group of diseases characterized by characteristic optic nerve atrophy and visual field defects, and pathologically elevated intraocular pressure is a major risk factor. Some people have high IOP but not glaucoma, while others never have high IOP but develop optic nerve atrophy and visual field defects, which are typical of glaucoma. Intraocular pressure fluctuates throughout the day and over time. Some people with high intraocular pressure in the early morning or at night, or with a wide range of fluctuations throughout the day, also have glaucoma. However, it is easy to miss the diagnosis.