Normal Tension Glaucoma Exam Review
Master normal tension glaucoma diagnosis, mimics, optic nerve findings, and the pressure-lowering target tested on board exams.
What is the defining feature of normal tension glaucoma?
Normal Tension Glaucoma in 30 Seconds
Normal tension glaucoma is glaucomatous optic neuropathy with corresponding visual field loss despite repeatedly normal measured intraocular pressure. It is a diagnosis of exclusion. Confirm open angles, document progression, and exclude pressure spikes and nonglaucomatous optic neuropathy before committing to the label.
Why Optic Nerve Damage Occurs Without High Pressure
Normal tension glaucoma, also called low-tension glaucoma, features glaucomatous optic neuropathy and visual field loss consistent with glaucoma despite intraocular pressure staying within the statistically normal range on repeated measurement. A susceptible optic nerve may be injured by pressure that is normal for most eyes but too high for that eye. Vascular dysregulation and reduced optic nerve head perfusion may also contribute. Normal tension glaucoma is now viewed as part of the primary open angle glaucoma spectrum, not a separate disease, so the optic nerve and visual field findings are fundamentally glaucomatous, and the distinction lies in the measured intraocular pressure rather than a different pattern of disease.
Differentiating Normal Tension Glaucoma From Look-Alikes
- Exclude previously unrecognized episodes of elevated intraocular pressure, including missed ocular hypertension, steroid response, pigment dispersion syndrome, pseudoexfoliation syndrome, or a prior resolved angle-closure episode.
- Confirm open angles with gonioscopy and review central corneal thickness, recognizing that thin corneas may underestimate Goldmann-measured intraocular pressure and independently increase glaucoma risk, along with treatment history, optic nerve photographs, optical coherence tomography, and repeatable visual fields.
- Exclude mimicking optic neuropathies, especially compressive lesions of the anterior visual pathway, ischemic optic neuropathy, hereditary optic neuropathy, and toxic or nutritional disease.
- Consider neuroimaging for atypical presentations, especially marked asymmetry, rapid progression, field loss respecting the vertical meridian, disc pallor greater than cupping, reduced central acuity, or a young patient, guided by clinical judgment rather than as a mandatory step in every case.
- Use diurnal intraocular pressure monitoring when clinically indicated to detect pressure peaks missed during routine office hours.
4 Facts Exams Always Ask
- Typical associations include older age, Asian ancestry, female sex, family history, myopia, low systemic blood pressure, migraine, Raynaud phenomenon, sleep apnea, and other vasospastic features.
- Defects may be deeper, more localized, and closer to fixation than in high tension glaucoma. Optic disc hemorrhages and focal rim notching are important progression clues.
- Intraocular pressure lowering remains the only treatment proven to slow progression. It reduces the pressure-related component of injury even when baseline pressure is statistically normal.
- The Collaborative Normal-Tension Glaucoma Study used a 30% intraocular pressure reduction target and showed reduced progression after accounting for cataract-related visual field effects.
The Classic Trap
Do not assume a normal intraocular pressure excludes glaucoma. The opposite error is also dangerous: do not label every cupped disc with normal pressure as normal tension glaucoma. The correct sequence is to confirm a glaucomatous structure-function pattern, check for missed pressure elevation, then exclude nonglaucomatous optic neuropathy when findings are atypical.
Clinical Pearl
A new disc hemorrhage in normal tension glaucoma is a warning sign, not a benign incidental finding. Recheck progression, adherence, nocturnal systemic hypotension risk, especially from excessive nighttime antihypertensive therapy, and whether the target pressure is low enough.
Checkpoint 1
An optic disc hemorrhage in a glaucoma patient is clinically important because it may indicate:
Checkpoint 2
Thin central corneal thickness is clinically important in ocular hypertension because it is associated with:
A 58-year-old woman with migraine has intraocular pressures of 14 mm Hg in both eyes on repeated visits. Her angles are open. The left disc has an inferior notch and disc hemorrhage. Visual field testing shows a dense superior paracentral defect threatening fixation. Magnetic resonance imaging is normal.
What management principle should guide treatment?
Sources & Reviewer Info
References
- Anderson DR. "Normal-tension glaucoma (Low-tension glaucoma)." Progress in Retinal and Eye Research. 2011.
- Hitchings RA, Anderton SA. "A comparative study of visual field defects seen in patients with low-tension glaucoma and chronic simple glaucoma." British Journal of Ophthalmology. 1983.
- Collaborative Normal-Tension Glaucoma Study Group. "The effectiveness of intraocular pressure reduction in the treatment of normal-tension glaucoma." American Journal of Ophthalmology. 1998;126(4):498-505.
- Ritch R, Shields MB, Krupin T. "Normal tension glaucoma: a practical approach." British Journal of Ophthalmology. 1998.
- Goyal A, Srivastava A, Sihota R, Kaur J. "Normal tension glaucoma: review of current understanding and mechanisms of the pathogenesis." International Journal of Ophthalmology. 2018.
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