The normal value for intraocular pressure is between 11-21 mmHg. 23 mmHg is considered mildly elevated, but it depends on the individual case. Some people have thicker corneas and are born with higher IOPs. Therefore, a mildly elevated IOP requires a corneal thickness measurement to see if the cornea is thicker than normal, and a single elevated IOP is not enough to explain the problem; repeated, multiple measurements are needed to determine that the elevated IOP is not accidental. In addition, outpatient IOP examinations are mainly non-contact jet examinations, and the clinical gold standard for IOP is mainly a pressure flattening tonometer, so elevated IOP can be considered to be measured using pressure flattening tonometry first, which will give a relatively more accurate value. If the pressure flattening IOP is also mildly elevated, a 24-hour ambulatory IOP measurement can be considered to see the fluctuation of the 24-hour IOP and determine whether glaucoma is present.