IOP is the most basic and important concept and variable in the entire process of glaucoma diagnosis, observation and follow-up, and assessment of treatment outcome. “Normal IOP is not a simple range of values, and its clinical value is not limited to an upper limit, but should be understood and understood in depth. For “normal IOP”, the most direct understanding of the general concept is that its normal range is 10-21 mmHg. Statistically, the normal range is the 95% reference range obtained by estimating the normal or approximately normal distribution data. However, in clinical practice, in many cases, for a specific patient, it is not only difficult to make a qualitative diagnosis of the disease based solely on its upper limit value of 21 mmHg, but also difficult to make a specific setting of the target IOP for treatment. In addition, a common feature of many studies is that the frequency distribution of IOP values in the general population of normal adults is age-dependent, with a normal distribution in the 20-40 age group and a mildly right skewed distribution with increasing age after 40 years. The right skewed distribution indicates that the IOP level can exceed the upper limit of normal by 21 mmHg in a few other normal individuals. Normal IOP has not only inter-individual variability, but also intra-individual variability, with intra-monocular fluctuations and inter-ocular symmetry, and the IOP shows dynamic changes around the clock. In addition, IOP is positively correlated with corneal thickness. In summary, it is best to go to the hospital to have your IOP evaluated by a professional ophthalmologist to see if it is normal and what level of IOP is controlled in glaucoma patients.