About this article
Medically reviewed- Written by
- Dr Paul Watson
- Medically reviewed by
- Dr Han Simpson
- Published
- August 20, 2026
- Medical review date
- September 8, 2026
- Evidence searched through
- September 8, 2026
- Next review due
- September 8, 2027
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- Worldwide
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Yes. Glaucoma can develop even when an eye-pressure reading falls within the range commonly described as normal.
John F. Doane, M.D., from Discover Vision Centers, works within a regional practice serving Missouri and Kansas. For someone searching for an eye doctor in Kansas City, a normal pressure result may feel reassuring, but the number alone cannot rule out glaucoma.
Glaucoma damages the optic nerve, which carries visual information from the eye to the brain. Higher pressure inside the eye is an important risk factor, but some people with elevated pressure never develop glaucoma. Others develop characteristic optic-nerve damage even though their recorded pressure has not exceeded the usual statistical range [1].
That is why a reassuring number on an examination report should be interpreted alongside the appearance of the optic nerve, family history, visual-field results, corneal measurements, and changes seen over time.
Why “normal” is a population range, not a guarantee
Eye pressure, also called intraocular pressure or IOP, is measured in millimeters of mercury. For most people, pressure above 21 mmHg is considered higher than the customary population range, but 21 is not a biological dividing line between healthy and unhealthy eyes [1].
A reading of 18 does not prove that the optic nerve is safe. A reading of 23 does not prove that glaucoma is present.
Eye-pressure measurements can change during office hours, while corneal thickness and the tonometer used can influence the result [2]. One result is therefore a snapshot rather than a complete record.
This explains why glaucoma screening based only on tonometry, the test used to measure eye pressure, can miss some people with the disease while flagging others who do not have it. The National Eye Institute states that tonometry alone is not sufficient for an accurate glaucoma diagnosis because the pressure considered normal varies among individuals [3].
A normal pressure result is only one part of the assessment. The clinician also considers family history, examines the optic nerve, and may use imaging or a visual-field test to look for damage.
The number still matters. It helps clinicians estimate risk, establish a baseline, and decide whether pressure-lowering treatment may be useful. It simply cannot answer the entire question by itself.
What normal-tension glaucoma means
Normal-tension glaucoma is a form of open-angle glaucoma in which the optic nerve shows glaucomatous damage even though measured eye pressure remains within the statistically normal range.
The diagnosis is based on the pattern of nerve damage and corresponding visual-field loss, not on the pressure reading alone. Clinicians also need to consider other conditions that can resemble glaucoma, including certain optic-nerve disorders, retinal disease, previous injuries, medication effects, and neurological problems.
Researchers do not yet have one explanation for why some optic nerves are damaged at pressures that other eyes tolerate. Current thinking includes differences in optic-nerve structure, blood supply, vascular regulation, and individual susceptibility to pressure [4,5].
The National Eye Institute identifies several possible risk factors for normal-tension glaucoma, including a family history of the condition, low blood pressure, certain heart problems, and Japanese ancestry [4]. These factors do not establish a diagnosis, but they may affect how closely a person should be monitored.
The term “normal tension” does not mean pressure is irrelevant. Some optic nerves may be more vulnerable at pressures that fall within the usual population range, while blood flow and other pressure-independent factors may also contribute [4,5].
A landmark randomized clinical trial studied patients with normal-tension glaucoma whose disease was progressing or threatening important areas of vision. Lowering pressure by about 30 percent reduced glaucoma progression when cataract-related visual-field changes seen more often in the filtration-surgery group were accounted for [6]. The findings helped establish pressure reduction as a central treatment strategy even when the starting pressure is not conventionally high.
Normal-tension glaucoma does not progress at the same rate in every patient. Some people remain stable for years, while others show earlier changes in the optic nerve or visual field [5,6].
Follow-up is therefore individualized according to the appearance of the nerve, visual-field results, age, medical history, and evidence of progression.
Changes in side vision may appear slowly
Most open-angle glaucoma does not announce itself with sudden blur, pain, or redness. Early disease often has no noticeable symptoms.
Vision loss usually begins in parts of the peripheral, or side, visual field. Because peripheral loss can develop slowly, many people do not recognize that their vision is changing at first [7].
This is one reason glaucoma cannot safely be ruled out by saying, “I can still see clearly.” Central reading vision may remain useful while smaller areas of peripheral vision have already changed.
When loss becomes more advanced, a person might notice difficulty seeing objects approaching from the side, navigating dim spaces, finding steps, or driving in complex traffic. These experiences are not specific to glaucoma and should not be used for self-diagnosis. Cataracts, retinal disease, neurological conditions, and other problems can cause similar difficulties.
Visual-field loss from glaucoma also does not always resemble a neat outer ring gradually closing inward. A systematic review found that glaucoma can produce several characteristic patterns, including localized arcuate defects, nasal steps, and defects closer to central vision. Patterns can differ among glaucoma subtypes and stages [8].
Waiting until side vision feels obviously reduced is a poor detection plan. Glaucoma treatment can help prevent further loss, but it does not restore optic-nerve damage that has already occurred [7].
Family history is especially relevant here. Someone whose parent or sibling has glaucoma should tell the examining clinician, even if prior pressure readings were described as normal. The family diagnosis, age of onset, severity, and treatment history may all help place an individual reading in context.
Why optic-nerve imaging and visual-field tests matter
Glaucoma evaluation looks at both structure and function.
Optic-nerve examination and imaging assess structure. A dilated examination lets the clinician evaluate the nerve’s shape, color, rim tissue, and degree of cupping. Optical coherence tomography, commonly called OCT, creates detailed cross-sectional measurements of the retinal nerve fiber layer and related structures around the optic nerve.
These measurements can reveal thinning associated with glaucoma and provide a baseline for later comparison. Modern imaging has improved clinicians’ ability to detect and monitor structural change, but no scan should be interpreted in isolation. Normal anatomical variation, image quality, high myopia, segmentation errors, and other eye conditions can affect the result [9].
Visual-field testing assesses function. During the test, the patient looks at a fixed point and responds when small lights appear in different locations. The result maps areas where visual sensitivity is normal, reduced, or absent.
Visual-field results may improve between a patient’s first and second examinations as the test becomes more familiar. If an early result is unreliable or does not fit the rest of the examination, the clinician may repeat it before deciding that the defect is genuine [10].
The results become more useful when clinicians compare them across tests and over time. An OCT scan may show whether nerve tissue is becoming thinner. A visual-field test may show whether that structural change corresponds with reduced sensitivity. Optic-nerve photographs can document visible changes, while repeated pressure measurements show how IOP behaves across visits.
Each test adds a different piece of information. Tonometry measures pressure, while a dilated examination and OCT look for structural changes around the optic nerve. Visual-field testing checks how vision is functioning. Corneal-thickness and drainage-angle measurements help clinicians interpret the pressure result and identify the type of glaucoma being considered.
A normal result on one test does not automatically cancel an abnormal result on another. Clinicians look for a consistent pattern and, often, evidence of change over time.
Discover Vision Centers provides comprehensive eye examinations across its Missouri and Kansas practice. Its published information describes visual-field testing during medical eye care and glaucoma treatments that include selective laser trabeculoplasty and minimally invasive glaucoma surgery [11,12].
For someone with a family history, a suspicious optic nerve, or inconsistent pressure readings, access to diagnostic testing and ongoing medical follow-up is more relevant than any single number.
A normal pressure reading can be reassuring, but the more useful question is whether the optic nerve and visual field remain healthy over time.
References
[1] National Eye Institute. (2024, December 5). Glaucoma and eye pressure. https://www.nei.nih.gov/eye-health-information/eye-conditions-and-diseases/glaucoma/glaucoma-and-eye-pressure
[2] Kotecha, A., Crabb, D. P., Spratt, A., & Garway-Heath, D. F. (2009). The relationship between diurnal variations in intraocular pressure measurements and central corneal thickness and corneal hysteresis. Investigative Ophthalmology & Visual Science, 50(9), 4229–4236. https://doi.org/10.1167/iovs.08-2955
[3] National Eye Institute. (2025, October 27). National Eye Institute statement on detection of glaucoma and adult vision screening. https://www.nei.nih.gov/about/education-and-outreach/glaucoma-resources/national-eye-institute-statement-detection-glaucoma-and-adult-vision-screening
[4] National Eye Institute. (2024, December 5). Types of glaucoma. https://www.nei.nih.gov/eye-health-information/eye-conditions-and-diseases/glaucoma/types-glaucoma
[5] Leung, D. Y. L., & Tham, C. C. (2022). Normal-tension glaucoma: Current concepts and approaches. A review. Clinical & Experimental Ophthalmology, 50(2), 247–259. https://doi.org/10.1111/ceo.14043
[6] Collaborative Normal-Tension Glaucoma Study Group. (1998). The effectiveness of intraocular pressure reduction in the treatment of normal-tension glaucoma. American Journal of Ophthalmology, 126(4), 498–505. https://doi.org/10.1016/S0002-9394(98)00272-4
[7] National Eye Institute. (2025, November 26). Glaucoma. https://www.nei.nih.gov/eye-health-information/eye-conditions-and-diseases/glaucoma
[8] Vandersnickt, M. F., Van Eijgen, J., Lemmens, S., Stalmans, I., Pinto, L. A., & Vandewalle, E. M. (2024). Visual field patterns in glaucoma: A systematic review. Saudi Journal of Ophthalmology, 38(4), 306–315. https://doi.org/10.4103/sjopt.sjopt_143_24
[9] Yuksel Elgin, C., Chen, D., & Al-Aswad, L. A. (2022). Ophthalmic imaging for the diagnosis and monitoring of glaucoma: A review. Clinical & Experimental Ophthalmology, 50(2), 183–197. https://doi.org/10.1111/ceo.14044
[10] Kulze, J. C., Stewart, W. C., & Sutherland, S. E. (1990). Factors associated with a learning effect in glaucoma patients using automated perimetry. Acta Ophthalmologica, 68(6), 681–686. https://doi.org/10.1111/j.1755-3768.1990.tb01694.x
[11] Discover Vision Centers. (n.d.-a). Facts about Discover Vision Centers. https://www.discovervision.com/facts/
[12] Discover Vision Centers. (n.d.-b). Routine eye care exams in Kansas City, Missouri. https://www.discovervision.com/routine-eye-care-kansas-city/eye-exams/