The most important danger of glaucoma is the impairment of visual function, which is manifested by loss of vision and reduction of visual field. Acute loss of vision usually occurs when the IOP is acutely elevated, accompanied by eye distention, headache, nausea and vomiting. Acute persistent high IOP can severely affect the metabolism of the optic cells, resulting in severe vision loss or blindness. Chronic persistent high IOP has insignificant effects on central vision in the early stages and progressive optic nerve atrophy in the middle and late stages, gradually leading to enlarged visual field defects, i.e., reduced range or absence when looking at objects. The loss of vision and visual field defects caused by glaucoma cannot be reversed and restored with the current level of medical technology. Early detection and timely treatment is therefore a key to preventing blindness from glaucoma. Early diagnosis and timely treatment may bring the condition under control to the greatest extent possible.