Since glaucoma usually results from an increase in inner eye pressure, or intraocular pressure (IOP), normal-tension glaucoma (NTG) is something of a mystery. NTG is a type of open-angle glaucoma that occurs when there is damage to the optic nerve—despite your eye pressure being in the normal range of 12-22 mm Hg.* 

Once considered rare, research has since revealed that almost one-third of glaucoma patients have NTG, and nearly two-thirds of Japanese glaucoma patients have received an NTG diagnosis.

What are the causes of and risk factors for normal-tension glaucoma?

Experts are still uncertain as to what causes NTG, but studies show that high-risk factors include:

• Family history of normal-tension glaucoma
• Japanese ancestry
• Personal history of systemic heart disease

Other possible risk factors are:

• Vasospastic events (when arterial spasms lead to constriction of blood vessels)
• Hypoperfusion (reduced blood flow)
• Nocturnal hypotension (when your blood pressure drops while you sleep)
• Hypercoagulability (higher than normal tendency of blood to form clots)
• Increased blood viscosity (higher blood thickness, or increased resistance against flow)

Research has also found an association between NTG and migraine headaches, Raynaud’s phenomenon, diffuse cerebral ischemia, and several autoimmune disorders, but the nature of that association is still uncertain.

How is NTG diagnosed?

Two common tests administered to diagnose NTG include:

• Ophthalmoscopy, in which the doctor holds a small device (ophthalmoscope) close to your eye to evaluate the color and shape of your optic nerve
• Visual field test, during which the doctor shines a light from various locations around your field of vision to check for areas of sight loss

Distinguishing features of NTG that aid in diagnosis include: 

• Visual field defects usually appear deeper, steeper, and closer to fixation than in patients with primary open-angle glaucoma. 
• The amount of visual field loss tends to be greater than what would be expected from the optic nerve’s appearance alone.
• Ophthalmoscopy readings show more localized defects of the retinal nerve fiber and a greater penchant for optic disc hemorrhages than do patients with primary open-angle glaucoma.

A complete ophthalmologic exam should help exclude other conditions, as well as events that could mimic NTG, like medication side effects. 

How is NTG treated?

The primary goal of treatment for NTG is to minimize vision loss and slow or stop the progression of the disease by lowering eye pressure (despite the pressure already being within normal range) treating underlying conditions that may be contributing factors.

These underlying conditions include:

• • Anemia
  • Arrhythmia
  • Hypothyroidism
  • Autoimmune diseases
  • Migraines

Treatment options typically include:

• Medications
  • Prostaglandin analogs
  • Alpha 2 agonists
  • Carbonic anhydrase inhibitors
  • Miotics
  • Beta blockers
  • Calcium channel blockers
• Laser treatments
• Filtration surgery 

Additional information on normal-tension glaucoma can be found on the American Academy of Ophthalmology and BrightFocus Foundation websites.

*Anderson, D. R. (2018, Dec. 10). Normal-Tension Glaucoma (NTG). Glaucoma Research Foundation. https://www.glaucoma.org/glaucoma/normal-tension-glaucoma.php

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