Normal-Tension Glaucoma

Overview

Normal-tension glaucoma (NTG) is a progressive optic neuropathy with the characteristic optic disc cupping and visual field loss of glaucoma, occurring in the absence of elevated intraocular pressure (IOP) — implying that mechanisms beyond mechanical stress on the optic nerve contribute to axonal loss.¹ It exists on a continuum with primary open-angle glaucoma, and the distinction from POAG is somewhat arbitrary given that individual susceptibility to IOP-related damage varies.

Epidemiology & Risk Factors

NTG is more common in some populations (notably reported at higher relative rates in Japanese cohorts) than others, though it occurs worldwide. Risk factors overlap with POAG (family history, older age, myopia) but NTG has additional associations with vascular dysregulation phenomena: migraine, Raynaud phenomenon, nocturnal systemic hypotension, and sleep apnea are all recognized associations reflecting a vasculopathic contribution distinct from classic mechanical IOP-driven damage.¹

Pathophysiology

Primary vascular dysregulation (PVD) — a constitutional impairment of vascular tone regulation independent of structural vascular disease — is increasingly recognized as a central pathogenic contributor in a substantial proportion of NTG patients.¹ Proposed mechanisms include impaired autoregulation of optic nerve head perfusion, elevated endothelin-1 with relative nitric oxide deficiency, defective neurovascular coupling, mitochondrial dysfunction, oxidative stress, exaggerated nocturnal hypotension, and autonomic nervous system imbalance.¹ This vascular phenotype (sometimes termed Flammer syndrome when features extend beyond the eye) helps explain why optic nerve damage can progress despite well-controlled, statistically normal IOP: reduced or unstable ocular perfusion pressure may itself damage the optic nerve head independent of mechanical IOP effects.

Clinical Presentation

NTG is typically asymptomatic until relatively advanced visual field loss develops, similar to other forms of open-angle glaucoma. Patients with a vasculopathic (PVD-associated) phenotype may report cold extremities, migraine with aura, or other features of Flammer syndrome, which can be a useful historical clue prompting consideration of NTG in a patient with normal IOP but a suspicious disc.

Exam Findings

• Optic disc cupping with normal-range IOP on repeated measurements (including diurnal curve assessment to exclude undetected IOP peaks)
• Optic disc hemorrhages (splinter/flame-shaped, at the disc margin) — a characteristic and relatively specific finding in PVD-associated NTG¹
• Focal, notch-type cupping (as opposed to the more diffuse cupping sometimes seen in high-tension glaucoma)
• Central and paracentral visual field defects, which can occur closer to fixation than typical POAG field loss and threaten central vision earlier
• Progressive damage despite documented normal/controlled IOP

Differential Diagnosis

• Primary open-angle glaucoma with undetected IOP peaks (diurnal IOP fluctuation missed on single measurements)
• Compressive optic neuropathy (pituitary or other intracranial mass) — should be excluded, especially with atrophy, pallor out of proportion to cupping, or an atypical field defect respecting the vertical midline
• Other causes of optic disc cupping/pallor: prior ischemic optic neuropathy, hereditary optic neuropathies
• Physiologic large cup-disc ratio without progressive damage

Management

Diagnosis requires confirming normal IOP on repeated measurements (ideally including diurnal curve assessment) alongside glaucomatous disc/RNFL and visual field findings, and reasonably excluding non-glaucomatous causes of optic neuropathy (neuroimaging is warranted in atypical presentations). IOP reduction remains the only proven treatment for slowing NTG progression, following the same general principles as POAG management (topical medications, laser trabeculoplasty, or surgery), even though IOP is already statistically normal — lowering it further still reduces the mechanical component of stress on a vulnerable optic nerve.

Minimally invasive glaucoma surgery (MIGS), alone or combined with cataract surgery, has shown efficacy in NTG: a meta-analysis found MIGS alone reduced IOP by approximately 2.6 mmHg and MIGS combined with phacoemulsification reduced IOP by approximately 2.1 mmHg, with meaningful reductions in the number of IOP-lowering medications needed, and no significant difference in efficacy between the two approaches.²

For patients with a PVD/vasculopathic phenotype (disc hemorrhages, migraine, cold extremities, documented nocturnal hypotension), addressing vascular contributors is an emerging adjunctive strategy: optimizing nocturnal systemic blood pressure (avoiding excessive nighttime BP lowering from systemic antihypertensives), lifestyle modification, and stress reduction are reasonable non-pharmacological measures, while pharmacological options such as calcium channel blockers, Ginkgo biloba extract, and endothelin receptor antagonists have shown benefit in selected cohorts, though robust randomized trial data in phenotypically defined populations are still needed before these become standard practice.¹

Complications

• Progressive central/paracentral visual field loss, which can threaten central vision earlier than typical POAG given its field defect pattern
• Continued progression despite normal/controlled IOP if the vascular contribution is not recognized or addressed
• Diagnostic delay or misattribution if a compressive or other non-glaucomatous cause is not excluded

Clinical Pearls

• Disc hemorrhages, focal notch-type cupping, and central/paracentral field defects are relatively characteristic findings pointing toward a PVD-associated NTG phenotype¹
• Ask about migraine, cold extremities, and other Flammer syndrome features — these support a vasculopathic contribution and can guide additional management considerations
• Excessive nocturnal systemic blood pressure lowering (from aggressive antihypertensive dosing) can worsen NTG by reducing optic nerve head perfusion pressure overnight — review a patient's antihypertensive regimen and timing
• IOP reduction is still the only proven treatment for NTG — vascular-targeted therapies remain adjunctive and evidence-based standardization is still evolving¹
• Always consider neuroimaging in atypical NTG presentations (e.g., pallor disproportionate to cupping, field defects respecting the vertical midline) to exclude a compressive lesion

Common Pitfalls

• Assuming "normal" single-visit IOP excludes glaucoma without considering diurnal IOP fluctuation
• Failing to exclude compressive optic neuropathy in atypical presentations
• Treating all NTG patients identically without recognizing the PVD/vasculopathic subgroup that may benefit from additional vascular-focused management
• Overlooking a patient's antihypertensive regimen as a potential contributor to nocturnal hypotension and optic nerve hypoperfusion
• Assuming vascular-targeted pharmacological therapies are established standard-of-care rather than emerging, selectively-applied adjuncts