Can a normal intraocular pressure (IOP), normal visual fields, and normal retinal computed tomography (CT) scan rule out glaucoma in a patient?

Can Normal IOP, Visual Fields, and Retinal Imaging Rule Out Glaucoma?

No, normal intraocular pressure, normal visual fields, and normal retinal imaging cannot definitively rule out glaucoma, as approximately half of all individuals with primary open-angle glaucoma have IOP levels below 22 mmHg, and glaucoma can exist with initially normal testing that later progresses. 1, 2

The Problem with "Normal" IOP

The traditional distinction between "normal" and "elevated" IOP is not supported by evidence:

• More than half of all glaucomatous eyes have screening IOP below 21 mmHg, whether receiving treatment or not 2
• The Baltimore Eye Survey demonstrated that roughly half of subjects with optic nerve damage from primary open-angle glaucoma had statistically "normal" IOP 2
• Normal tension glaucoma (NTG) represents a significant proportion of glaucoma cases, with IOP consistently measured below 22 mmHg 1

This is critical because relying solely on IOP measurements will miss a substantial portion of glaucoma patients.

Why Single "Normal" Tests Are Insufficient

Visual Field Limitations

• Visual fields may appear normal in early glaucoma before detectable functional loss occurs 3
• Glaucomatous damage must be confirmed with repeat and confirmatory visual field examinations before changing management 3
• A single normal visual field does not exclude early disease or future progression 3

Structural Assessment Challenges

• Optic nerve appearance and RNFL imaging provide complementary but different information about glaucoma status 3
• Early structural changes may be subtle and require serial monitoring to detect progression 3
• The American Academy of Ophthalmology emphasizes that diagnosis requires documentation of optic nerve status at presentation and ongoing monitoring for evidence of glaucomatous damage 3

The Glaucoma Suspect Paradigm

The concept of "glaucoma suspect" exists precisely because normal initial testing does not rule out disease:

• A glaucoma suspect is defined as having clinical findings or risk factors indicating increased likelihood of developing POAG, even with currently normal testing 3
• In the Ocular Hypertension Treatment Study, more than 90% of patients with untreated ocular hypertension did not progress over 5 years, but 9.5% did develop glaucoma despite initially having only elevated IOP without optic nerve or visual field damage 3

Critical Risk Factors That Demand Ongoing Surveillance

Even with "normal" baseline testing, the following warrant continued monitoring:

• Family history: 9.2-fold increased odds with a first-degree relative, 5-fold with two or more affected siblings 3, 4
• Thin central corneal thickness (CCT ≤510 μm): Higher risk independent of IOP measurement artifacts 3, 4
• Low diastolic perfusion pressure (<50 mmHg): Associated with higher POAG prevalence 3, 1
• Myopia: Particularly axial myopia with longer axial length 3
• Type 2 diabetes mellitus: 40-140% higher odds of POAG 3
• Age and ethnicity: African Americans and Latinos over 40, Caucasians over 65 4

The Clinical Algorithm

For any patient with normal IOP, visual fields, and imaging:

1. Measure central corneal thickness to assess both IOP measurement accuracy and independent risk 3, 4
2. Perform gonioscopy to confirm open angles and exclude angle-closure mechanisms 3
3. Document baseline optic nerve status with both clinical examination and imaging (photography and OCT provide complementary information) 3
4. Assess all risk factors systematically, including family history, perfusion pressure, diabetes, and myopia 3, 4
5. Establish appropriate monitoring intervals based on cumulative risk, not just current test results 3

Common Pitfalls to Avoid

• Do not use IOP correction nomograms based on corneal thickness—no validated correction formula exists 4
• Do not rely on single-time-point IOP measurements—IOP fluctuates considerably and maximal daily IOP often occurs outside office hours 5
• Do not assume a single normal visual field excludes disease—repeat testing is essential for confirmation 3
• Do not ignore risk factors when current testing appears normal—cumulative risk determines surveillance strategy 3, 4

The Bottom Line

Glaucoma is a progressive disease that requires longitudinal assessment. Normal testing at a single point in time establishes a baseline but does not exclude current early disease or future development of glaucoma, particularly in patients with risk factors. The diagnosis of "glaucoma suspect" exists specifically to capture patients who require ongoing monitoring despite currently normal findings 3. Serial monitoring of IOP, optic nerve structure, and visual function over time is the only way to truly assess glaucoma risk and detect early disease 3, 1.