From the Guidelines
Normal intraocular pressure (IOP) measured with a tonometer typically ranges between 10-21 mmHg. This range is widely accepted in the field of ophthalmology, as stated in the primary open-angle glaucoma preferred practice pattern 1. The upper limit of 21 mmHg is commonly used as a cutoff for normal IOP, although it's essential to note that some individuals may have glaucoma with pressures within the normal range, known as normal-tension glaucoma. On the other hand, some people may have elevated pressures without optic nerve damage, referred to as ocular hypertension 1.
When measuring IOP, it's crucial to consider the type of tonometer used, as different devices can produce varying results. Goldmann applanation tonometry is considered the gold standard, while non-contact tonometry and handheld devices like Tono-Pen are also commonly used 1. Additionally, corneal thickness can impact IOP measurements, with thicker corneas potentially resulting in higher readings and thinner corneas in lower readings. Diurnal variations in IOP are normal, with pressures typically highest in the early morning and lowest in the evening, varying by 2-6 mmHg throughout the day 1.
Key points to consider when evaluating IOP include:
- The upper limit of normal IOP is 21 mmHg
- Different tonometers can produce varying results
- Corneal thickness can impact IOP measurements
- Diurnal variations in IOP are normal
- Regular IOP monitoring is essential for glaucoma diagnosis and management, as elevated IOP is the primary modifiable risk factor for glaucoma progression 1.
From the Research
Normal IOP Values
- Normal intraocular pressure (IOP) values range from 10 to 21 mmHg, with a mean of 15.5 mmHg +/- 2 standard deviations 2
Factors Influencing IOP Measurement
- IOP values are influenced by various factors, including:
- Patient's position during measurement
- Central corneal thickness
- Corneal diameter and curvature
- Rigidity of the cornea
- Cornea's state of hydration 2
IOP Measurement Techniques
- Several techniques and devices are available for determining IOP, including:
- Goldmann applanation tonometry (considered the gold standard)
- Noncontact tonometry
- Tono-Pen
- ICare tonometer
- Dynamic contour tonometry
- TGDc-01 tonometry
- Ocular response analyzer 2