Does high intraocular pressure mean glaucoma? Can I rule out glaucoma if my intraocular pressure is not high? First of all, let’s explain what intraocular pressure means: intraocular pressure is the pressure generated by the contents of the eye on the wall of the eye. The contents of the eye include the atrial fluid, lens, and vitreous humor. The lens and vitreous are relatively stable, so fluctuations in IOP are mainly influenced by atrial fluid. The role of IOP is to maintain the shape and normal physiological function of the eye, so it must be kept within a constant range, not too high and not too low. It is like a balloon, IOP is the gas inside, with the support of gas, pressure on the wall of the ball, the balloon can bulge, if the gas is less, the ball will deflate, if the gas is too much, there is the possibility of bursting at any time. Normal intraocular pressure is 10-21mmHg (1.33-2.78Kpa), the pressure difference between the two eyes is 4-5mmHg (0.53-0.67Kpa), the difference between day and night fluctuations 8mmHg (1.07Kpa), the intraocular pressure exceeds the normal range, it is generally considered to have glaucoma. IOP is an important basis for the diagnosis of glaucoma, but it is not the only factor, and it cannot be used mechanically to determine whether glaucoma is caused by IOP. There is a clinical type of glaucoma in which the IOP remains within the normal range until blindness, which we call “normal IOP glaucoma”, because the underlying IOP is low and even if it is within the fluctuating range of normal IOP, it is still enough to cause damage to the fundus. There is another type of glaucoma with high IOP, but without any clinical manifestations of glaucoma and damage to the fundus, which we call “hypertensive glaucoma”, and only 10% of people with hypertensive glaucoma develop glaucoma. Therefore, IOP is an indispensable and important basis for the diagnosis of glaucoma, but it is not the only basis.