What is Considered Elevated Intraocular Pressure?
Elevated intraocular pressure (IOP) is defined as IOP greater than 21 mmHg, which represents more than two standard deviations above the population mean. 1
Standard Definition and Context
IOP >21 mmHg is the conventional threshold used in the United States to define ocular hypertension when there is no evidence of optic disc or visual field damage 1
This cutoff is based on statistical distribution (the highest 97.5th percentile) rather than a pathological threshold, making it an arbitrarily defined level 1
The American Academy of Ophthalmology guidelines consistently use this 21 mmHg threshold across multiple practice patterns for defining elevated IOP in glaucoma suspect populations 1
Critical Clinical Limitations
The 21 mmHg cutoff has poor predictive value and should never be used in isolation for clinical decision-making. 1
Population studies show enormous variability: only 13-71% of patients with IOP >21 mmHg actually have glaucomatous optic nerve damage, depending on the population studied 1
Using IOP >21 mmHg as a screening cutoff demonstrates only 47.1% sensitivity, meaning more than half of glaucoma cases are missed 2
Conversely, approximately 50% of glaucoma patients have IOP in the "normal" range (≤21 mmHg), which can provide false reassurance if IOP alone is relied upon 2
Individual Susceptibility Varies Dramatically
There is great interindividual variation in optic nerve susceptibility to IOP-related damage 1
The Baltimore Eye Survey demonstrated that at IOP of 30 mmHg, only 7% of Caucasians but 25% of African Americans had glaucoma, highlighting how the same pressure level affects different individuals differently 1
Elevated IOP is a risk factor for glaucoma, not a diagnostic criterion—many people with elevated IOP never develop optic nerve damage 1
Clinical Application
When elevated IOP is identified, comprehensive evaluation must include:
Optic nerve head and retinal nerve fiber layer assessment (structural evaluation) 1, 2
Gonioscopy to evaluate the anterior chamber angle 1
Assessment of additional risk factors: age, family history, race/ethnicity (African American or Latino/Hispanic), thin central cornea, diabetes, myopia, and low ocular perfusion pressure 1
Do not screen or diagnose glaucoma based on IOP measurement alone—this approach misses the majority of cases and provides false reassurance to half of actual glaucoma patients 2