Is Measuring IOP Enough for Glaucoma Screening?
No, measuring intraocular pressure (IOP) alone is not an effective method for screening populations for glaucoma, particularly in individuals with a family history who are at higher risk. 1
Why IOP Measurement Fails as a Standalone Screening Tool
The American Academy of Ophthalmology explicitly states that measuring IOP is not an effective method for screening populations for glaucoma, with poor sensitivity that misses the majority of cases. 1
Critical Performance Limitations
Using an IOP cutoff above 21 mmHg demonstrates only 47.1% sensitivity and 92.4% specificity for diagnosing primary open-angle glaucoma (POAG), meaning more than half of glaucoma cases are missed. 1
Half of all individuals with POAG have IOP levels below 22 mmHg at the usual screening cutoff, whether they are receiving treatment or not. 1, 2
Most individuals with elevated IOP at screening do not have and may never develop optic nerve damage, with only 1 in 10 to 15 individuals with elevated IOP showing demonstrable optic nerve damage. 1
Why This Matters for High-Risk Individuals
For individuals with a family history of glaucoma, the stakes are even higher. The American Academy of Ophthalmology notes that first-degree relatives of those with POAG have 9.2-fold higher odds of having glaucoma, and screening is more cost-effective when targeted at high-risk populations including those with family history. 1
The Risk of False Reassurance
Relying on IOP alone provides false reassurance to approximately 50% of glaucoma patients whose pressures fall in the "normal" range, delaying diagnosis until irreversible vision loss occurs. 1, 2
The U.S. Preventive Services Task Force emphasizes that many persons with POAG do not have increased IOP, making tonometry alone inadequate to detect all cases. 1
What Comprehensive Screening Should Include
The American Academy of Ophthalmology identifies three main approaches that should be used in combination: measuring IOP, assessing the optic nerve head (ONH) and retinal nerve fiber layer (RNFL), and evaluating the visual field. 1
Essential Components Beyond IOP
Assessment of the ONH and RNFL is critical, as structural changes precede functional visual field loss and can identify glaucoma in patients with normal IOP. 3, 4
Visual field testing detects functional deficits, with characteristic patterns including arcuate scotomas, nasal steps, and paracentral scotomas that respect the horizontal midline. 4
Frequency doubling technology perimetry shows promise as a screening tool for moderate to severe glaucomatous damage and does not require correction of moderate refractive error. 1
Common Pitfalls to Avoid
Do not use a single IOP measurement to rule out glaucoma, especially in high-risk patients with family history, as IOP fluctuates considerably and peak pressures often occur outside office hours. 5
Do not assume "normal" IOP means no glaucoma risk—the traditional distinction between "normal" and "elevated" pressure is not supported by population-based evidence. 2
Do not screen with IOP alone in African Americans, Hispanics, older adults, or those with family history—these populations warrant comprehensive evaluation including structural and functional assessment. 1
Recommended Approach for Family History Patients
Individuals with a family history of glaucoma should undergo comprehensive eye examinations by eye care professionals that include dilated ophthalmoscopy or slit lamp examination of the optic disc, visual field testing, and IOP measurement as part of a multimodal assessment. 1
The Centers for Medicare and Medicaid Services recognizes this need by covering glaucoma examinations for beneficiaries with a family history of glaucoma. 1
Screening should be performed by eye care professionals rather than in primary care settings, as most tests available in primary care do not have acceptable accuracy to detect glaucoma. 1