The cause of glaucoma is caused by elevated intraocular pressure compressing the optic nerve. Therefore, IOP is an important basis for glaucoma diagnosis, treatment and review, and the development of glaucoma can only be controlled if IOP is controlled to a safe range. The higher the IOP, the more harmful it is to the eye, so IOP measurement is very important. IOP measurement principles: IOP should be a routine ophthalmic examination, and normal people over the age of 40 should be examined once a year, preferably at different times of the day, and 24-hour IOP should be measured if necessary. A few questions about IOP: 1. In the vast majority of cases, high IOP will cause glaucoma, and the higher the IOP, the more severe the glaucoma. 2. There are a few special people for whom high IOP does not cause glaucoma. Although the IOP has exceeded the upper limit of normal (21mmHg), long-term observation does not show optic nerve damage, which is called normal high IOP, and this condition requires long-term observation to exclude glaucoma. 3, there are also a few special patients with normal IOP may also be glaucoma. These patients have poor tolerance for IOP, even if the IOP is normal, but exceeds his tolerance range and typical glaucomatous optic nerve damage occurs, which is called normal IOP glaucoma. 4. High IOP at one time is not necessarily glaucoma, but requires several repeated examinations to determine.