A high IOP is a high pressure inside the eye. IOP is the balanced pressure exerted by the eye contents on the wall of the eye, that is, the pressure inside the eye. Under normal circumstances, IOP is stabilized within a certain range to maintain the normal shape and physiological function of the eye. The contents of the eye include atrial fluid, lens, and vitreous humor, of which the atrial fluid is the one that plays a role in regulating intraocular pressure. The atrial fluid is produced by the ciliary protrusion of the ciliary body, flows into the posterior chamber, then into the anterior chamber through the pupil, and finally is discharged through the anterior chamber angle trabecular network. The production and excretion of atrial fluid is a dynamic balance, that is, the total amount of atrial fluid produced and discharged is equal in a certain time. If for some reason the discharge of atrial fluid is blocked or the amount produced increases, this can lead to a buildup of atrial fluid and an increase in intraocular pressure. Intraocular pressure is volatile, and body position, forceful blinking, eye rubbing, light, and water intake can affect IOP. Normal IOP is 10mmHg-21mmHg (1.33kPa-2.80kPa), with a mean value of 15.8mmHg (1mmHg≈0.133kPa) and a standard deviation of 2.6mmHg, and the pressure difference between the two eyes is <4mmHg-5mmHg ( 0.53kPa-0.67kPa), and an IOP difference of <8mmHg over a 24-hour day. if it is higher than the above range, it is considered high IOP. Therefore, high IOP generally refers to abnormal atrial water balance resulting in high pressure exerted by the eye contents on the wall of the eye.