From the Guidelines
Normal intraocular pressure (IOP) typically ranges between 10 to 21 mmHg, with an average of about 15-16 mmHg, as stated in the most recent guidelines 1. This pressure is essential for maintaining the eye's shape and proper functioning. IOP is created by the balance between aqueous humor production by the ciliary body and its drainage through the trabecular meshwork and uveoscleral pathway. Some key points to consider regarding IOP include:
- Pressures consistently above 21 mmHg are considered ocular hypertension, which is a risk factor for developing glaucoma, as noted in 1 and 1.
- However, some individuals can develop glaucomatous damage even with pressures in the normal range (normal-tension glaucoma), while others may have elevated pressures without developing optic nerve damage.
- IOP naturally fluctuates throughout the day, typically being highest in the early morning and lowest in the evening, and can also be affected by factors such as body position, exercise, fluid intake, and certain medications.
- Regular measurement of IOP is an important part of comprehensive eye examinations, especially for individuals over 40 or those with a family history of glaucoma, as emphasized in 1 and 1. It's also important to consider that the decision to treat a glaucoma suspect patient depends on the level of IOP and other associated risk factors, or evidence of change of the optic nerve, retinal nerve fiber layer (RNFL), or visual field indicating the development of POAG, as discussed in 1. A reasonable target for IOP reduction in a POAG suspect patient in whom the decision to treat has been made is 20%, based on the OHTS, as mentioned in 1. Overall, maintaining a healthy IOP is crucial for preventing glaucoma and preserving vision, and individuals should consult with an eye care professional for personalized advice on managing their IOP, as recommended in 1.
From the Research
Definition of Normal Intraocular Pressure
- Normal intraocular pressure is defined as between 10 and 21 mmHg, which is two times the standard deviation of the mean intraocular pressure in the normal population 2.
- Normal IOP values range from 10 to 21 mmHg (15.5 mmHg+/-2 SD) 3.
Factors Influencing Intraocular Pressure
- Intraocular pressure is influenced by various factors, including the patient's position during measurement, central corneal thickness, corneal diameter and curvature, rigidity of the cornea, and the cornea's state of hydration 3.
Measurement of Intraocular Pressure
- Tonometry is the measurement of intraocular pressure (IOP), with Goldmann applanation tonometry being the gold standard for intraocular pressure measurement 3.
- Other methods for determining IOP include noncontact tonometry, the Tono-Pen, the ICare tonometer, dynamic contour tonometry, TGDc-01 tonometry, and the ocular response analyzer 3.
Clinical Significance of Normal Intraocular Pressure
- Normal tension glaucoma (NTG) is a subvariant of primary open angle glaucoma (POAG) or a separate entity, defined as chronic open angle glaucoma without elevated intraocular pressure or normal intraocular pressure 2.
- The primary goal of treatment for NTG is the reduction of intraocular pressure, which can stop the disease 2.