Recent studies have shown that nighttime IOP is higher than daytime IOP, with the trough of IOP at the end of the day and the peak at the end of sleep in the early morning. This fluctuation exists in both the sitting and lying positions and the pattern of fluctuations is similar in both. The mechanism of these fluctuations is not well understood and may be related to changes in adrenocorticotropic hormone levels and resistance to atrial outflow channels. Studies have shown that plasma glucocorticoid fluctuations parallel changes in IOP, with peaks 3-4 hours earlier than the latter. Disruption of normal glucocorticoid fluctuations results in corresponding changes in IOP. The application of glucocorticoid inhibitors can lower IOP. It has been found that the level of IOP at night is related to the period of sleep, with the lowest IOP during fast-acting eye sleep and the peak occurring in slow-wave sleep. The trend of IOP fluctuations in healthy individuals aged 18-25 and 50-69 years old were studied respectively, and the diurnal IOP showed a clear rhythm, but the fluctuation of IOP in the 24-hour recumbent position was only (3.4±0.7 mmHg) with no clear rhythm, suggesting that the increase of nocturnal IOP may be related to the conversion from daytime standing to nocturnal recumbent position, and this change of position will increase the suprascleral venous pressure leading to the increase of IOP This point is also an important cause of nocturnal IOP elevation. Changes in position can cause changes in IOP, mainly related to changes in superior scleral venous pressure. In normal subjects, the superior scleral venous pressure is 7-14 mmHg, which is the only factor that is affected by position among the factors that constitute the resistance to atrial outflow. When the position changes from sitting to lying, the upper scleral venous pressure increases by 3-6 mmHg, and this fluctuation remains stable with a small fluctuation while the position remains unchanged. To evaluate nocturnal IOP, IOP measurements should be taken in the prone position, as the nocturnal sleep position is prone. When measured in the sitting position, the IOP value may be 2-3 mmHg lower than the true value, which affects the accuracy of the peak IOP measured by the IOP curve. However, since neither non-contact nor flattened tonometers can now measure nocturnal recumbent IOP, using immediate sitting IOP as the nocturnal IOP for 24-hour IOP is clinically significant and has relatively little error. IOP is influenced by many factors and fluctuates periodically from day to night. The normal value of 24-hour IOP fluctuation range in Chinese is ≤ 4 mmHg (1 mmHg = 0.133 kPa). A fluctuation range > 8mmHg is considered pathological IOP. Therefore, in order to truly understand the IOP value of a patient, it is necessary to take into account that IOP is actually a continuous value when evaluating it. 24-hour IOP monitoring can provide clinical diagnosis and treatment with a base state before treatment, including the peak IOP, the timing of the peak IOP and the magnitude of IOP fluctuations, thus providing detailed information for individualized treatment.