Glaucoma refers to damage to the optic nerve in the eye. Usually, this occurs along with raised pressure inside the eye, but in normal tension glaucoma, pressure in the eye is within the typical range.

Scientists do not fully understand the cause of normal tension glaucoma.

Often, it does not cause symptoms to begin with, but it can lead to eye damage and vision loss.

In this article, we will explain what normal tension glaucoma is, the symptoms, risk factors, and treatments.

An older man covering one eye due to normal tension glaucoma.Share on Pinterest
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Glaucoma is an eye condition in which damage occurs to the optic nerve in the eyes. Normal tension glaucoma (NTG) is a form of the condition where pressure inside the eye falls within a typical range of less than 21 millimeters of mercury (mm Hg).

With other forms of glaucoma, pressure inside the eye increases, leading to vision loss. Intraocular pressure does not rise in NTG, but vision loss can still occur.

Another characteristic of NTG is that it is an open angle type of glaucoma. In open-angle glaucoma, the angle between the iris, or colored part of the eye, and the cornea (the transparent part of the eye covering the iris) is 20–45°.

NTG is more common in some groups than others. For instance, reports suggest that around 2.3% of the population in Asia experience primary open-angle glaucoma (POAG), with NTG making up more than 70% of these cases. Around 2% of white Europeans also have POAG, but only about 33% of these are NTG cases.

In Africa, around 3–8% of people have POAG, and around 50% of these are NTG cases. Studies have not yet explored why these differences exist. However, researchers think that as life expectancy increases, POAG and NTG will become more common in general.

Other names for the condition include normal pressure glaucoma, low tension glaucoma, or low pressure glaucoma.

To begin with, people with NTG often have no symptoms. A doctor may have noticed some potential signs of glaucoma during an eye exam, leading a person to seek a diagnosis.

When symptoms do occur, people do not always notice them. This is because the symptoms can begin gradually and may only affect one eye. If the condition does not affect the other eye, a person’s vision may seem typical.

One of the main potential symptoms of NTG is vision changes or loss. This can include:

  • difficulty seeing in low-contrast situations, such as when driving at night
  • difficulty adjusting to extremely bright or low light
  • glare from bright light
  • changes in a person’s peripheral vision or visual field

Researchers have not yet worked out how the disease process works in NTG. Even though intraocular pressure (within the eye) in people with NTG is in the typical range, it may still play a role in the cause of the condition.

Additionally, evidence suggests that as many as 21 in 100 people with NTG have a family history of glaucoma, which indicates that it has a genetic component.

It is likely that multiple factors lead to nerve-cell loss in the retina, causing NTG. Other mechanisms that may play a role in the condition include:

  • vascular dysregulation
  • intracranial pressure, which is the pressure inside the skull
  • atypical functioning of the lamina cribrosa, which is a mesh-like structure at the optic nerve head that supports the cells that form the optic nerve
  • neurodegenerative disorders, such as Alzheimer’s disease
  • metabolic disorders, such as metabolic syndrome
  • oxidative stress

Many people with NTG also have conditions that affect blood vessels, suggesting a vascular link. These conditions include:

  • migraine
  • high blood pressure (hypertension)
  • low blood pressure at night (nocturnal hypotension)
  • Raynaud’s phenomenon, which is a condition that causes decreased blood flow in the fingers
  • optic nerve hemorrhages

Other risk factors include:

  • older age
  • being female
  • thin central corneal thickness
  • above-average intraocular pressure, even if it still falls within a typical range
  • obstructive sleep apnea, which is a condition in which the throat narrows during sleep, disrupting breathing

Usually, doctors can diagnose NTG by looking at the condition of the optic nerve, but sometimes they need to investigate further to confirm. For instance, they may order brain imaging tests to rule out other causes of a person’s optic nerve impairment.

Generally, however, doctors tend to do the same tests for NTG as they do to confirm POAG. This means carrying out:

  • a comprehensive eye exam
  • optic nerve imaging
  • visual field testing

Treating NTG focuses on reducing a person’s intraocular pressure from their baseline reading to prevent the disease from getting worse. Many medications or eye drops can potentially help with this.

Doctors often prescribe a type of medication known as a prostaglandin analogue, such as latanoprost, to treat NTG. Additionally, studies have shown brimonidine (Alphagan) to have a protective effect on the optic nerve.

If medication does not work, doctors may consider laser treatment or a surgical procedure, such as trabeculectomy, to lower the person’s eye pressure. Trabeculectomy involves creating a new drainage path for the eye to reduce pressure.

Below are some answers to some common questions.

Is normal tension glaucoma harder to treat?

NTG glaucoma can be difficult to treat due to the treatment options only being to lower pressure in the eyes. This can be less helpful in NTG than in other types of glaucoma.

How many people go blind due to NTG?

Research has shown that even without treatment, 65 in 100 people with NTG do not experience disease progression.

Only 12 in 100 people who have treatment to reduce their eye pressure go on to develop worse NTG. This can potentially occur if a person does not use their medications or does not receive regular follow-up appointments.

Many people with NTG do not experience significant vision loss and it does not get worse over time. For others, vision loss can occur and progress. In the most severe cases, people can become blind in both eyes.

Risk factors for worsening vision problems include having migraine or experiencing optic disc hemorrhage.

Normal tension glaucoma (NTG) refers to damage to the optic nerve that occurs without an increase in pressure inside the eye. This is different from other types of glaucoma, in which the pressure increases.

That said, treatment to prevent the disease from getting worse usually involves lowering a person’s eye pressure anyway to decrease the chance of vision loss.

Treatment may include medications or surgery, but even without treatment, the disease does not get worse in 65% of people.