Understanding Normal-Tension Glaucoma: Symptoms, Causes, and Treatment

Dinesh Patel
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Dr. Kaushal

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normal tension glaucoma

Glaucoma is a progressive eye disease that can cause irreversible vision loss if left untreated. 

While elevated eye pressure is often associated with Glaucoma, there is a lesser-known variant known as Normal-tension Glaucoma.

Even when eye pressure is within normal ranges, the optic nerve still suffers damage.

This article delves into the causes, symptoms, diagnosis, and treatment options and sheds light on this silent threat to vision.

Normal-tension Glaucoma

Normal-tension Glaucoma (NTG), or low-pressure Glaucoma, is a unique and often misunderstood eye condition. 

It is progressive optic nerve damage and visual field loss. 

Unlike other forms of Glaucoma, NTG occurs with intraocular pressure (IOP) levels within the normal range. 

This condition poses a significant risk of bilateral blindness and requires careful monitoring and treatment. 

Fact:
The normal intraocular pressure (IOP) typically falls within 10 to 21 millimeters of mercury (mmHg). However, normal pressure can vary slightly among individuals, and what is considered normal for one person may not be the same for another.

Symptoms of Normal-tension Glaucoma

Reduced vision in low lighting or glareSource: perfectlab_from_Getty_Images
Reduced vision in low lighting or glare

When people first discover they have NTG, they usually don’t feel symptoms. 

It’s often detected during routine eye exams or Glaucoma tests by an optometrist or as an unexpected finding by an eye specialist. 

Even if the disease has progressed somewhat, patients may not notice any problems because it can affect only one eye, create subtle vision issues, or develop gradually. 

Since the eye pressure (IOP) is in the normal range for NTG, doctors often become suspicious due to changes in the optic nerve’s appearance or when visual field tests show abnormalities.

In more advanced cases, patients might experience:

  • Reduced vision in low lighting or glare
  • Difficulty adjusting to very bright or dark conditions

Risk Factors for Normal-Tension Glaucoma

Several factors increase the risk of developing NTG:

  • Age: NTG is more common in older individuals.
  • Family history: A family history of Glaucoma raises the risk of Normal-Tension Glaucoma
  • Gender: Females are more susceptible to NTG
  • Thin central corneal thickness: Thinner corneas are associated with an increased risk of NTG
  • Systemic Hypertension: High blood pressure can also contribute
  • Nocturnal Hypotension: Low blood pressure during sleep can reduce optic nerve perfusion, potentially contributing to NTG
  • Migraine: A history of migraines is linked to NTG
  • Other medical conditions: Conditions like Raynaud’s phenomenon, frontotemporal and Alzheimer’s dementia, and obstructive sleep apnea may increase the risk
Warning:
Prolonged periods of low blood pressure during the night can reduce the blood supply to vital organs, including the heart and brain. This can cause severe health issues like strokes and heart attacks.

Causes

The exact cause remains uncertain, but several factors may contribute to its development. 

It is believed that some individuals may have optic nerves that are more sensitive or fragile, making them susceptible to damage even under normal pressure conditions. 

Additionally, abnormally low blood pressure, whether due to medication reactions or severe blood loss, could play a role in its occurrence. 

Poor blood circulation, often linked to conditions like atherosclerosis, can also harm the cells that transmit signals from the eye to the brain.

Diagnosis

Diagnosing Normal-tension Glaucoma requires a comprehensive eye examination conducted by an ophthalmologist. The examination includes:

Automated Perimetry

It helps check your peripheral (side) vision. 

In more advanced cases, they use the 10-2 or wide-field tests like the 30-2 and Estermann tests. 

Some newer tests are called SITA, and faster tests are quicker but just as accurate.

Stereoscopic fundus photos

Doctors take detailed pictures of the back of your eye, especially the optic nerve. 

These photos are a reference point for future exams, helping them see any changes over time.

OCT technology

This is a special imaging technique that helps monitor Glaucoma. 

It measures the layers of nerve cells in your eye. By comparing your results to a normal database, doctors can see if there are any issues with your optic nerve. 

Corneal Pachymetry

This measures the thickness of the clear front part of your eye, called the cornea. 

Thinner corneas are linked to a higher risk of Glaucoma progression. It’s also important because it can affect the accuracy of eye pressure measurements.

Monitoring eye pressure

In Glaucoma, eye pressure can vary during the day. 

Doctors may want to check your eye pressure multiple times daily to get a better picture of what’s happening. 

They can do this in their office or provide you with a device to measure it at home. There’s even a water-drinking test that can help simulate these pressure changes.

Treatment and management

Treatment for Normal-tension Glaucoma aims to slow down the disease and prevent vision loss

Not all cases of NTG will lead to significant vision problems. In some cases, close monitoring without treatment may be suitable.

Initial monitoring

In many NTG cases, especially when no sign of progression, doctors may start by closely monitoring the patient’s condition without immediate treatment. 

Regular check-ups are essential.

Eye pressure lowering

eye drops are common prescriptionSource: eternalcreative_from_Getty_Images
Eye drops

Lowering eye pressure (intraocular pressure or IOP) is the primary way to manage NTG. This can be achieved through:

  • Eye drops: Prescription eye drops can help reduce eye pressure. Prostaglandin analogs are commonly used as a first-line treatment
  • Laser treatments: Selective laser trabeculoplasty (SLT) or cyclo-diode laser can also be used to lower eye pressure
  • Surgery: In some cases where other treatments are ineffective, surgical procedures like augmented trabeculectomy may be necessary to achieve optimal eye pressure control
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Neuroprotective effects

Some treatments may have additional neuroprotective effects to help preserve optic nerve function. For example, the medication Brimonidine is hypothesized to have such an effect.

Non-IOP interventions

While reducing eye pressure is the main focus, there is ongoing research into other factors to treat NTG. These factors include:

  • Nocturnal Hypotension: Low blood pressure during the night may affect optic nerve health. Adjusting the timing of systemic anti-hypertensive medications or monitoring blood pressure patterns can be considered
  • Diet and Nutritional Supplements: Some studies are exploring the potential benefits of supplements like Nicotinamide (vitamin B3) and ginkgo biloba
  • Exercise: Regular exercise can lower eye pressure, but its impact on NTG progression is not fully understood
  • Meditation: Meditation has been shown to lower eye pressure, reduce pressure fluctuations, and have positive effects on neuroprotective markers
  • Smoking: Smoking may be associated with raised eye pressure and Glaucoma

Also read: It’s crucial to understand the available treatments for Glaucoma as you navigate your journey with the condition. Read Understanding the Glaucoma Treatment Options to know all about it.

Conclusion

Normal-tension glaucoma (NTG) is a unique and often misunderstood eye condition that can silently threaten your vision. 

Unlike other forms of Glaucoma, NTG occurs with normal eye pressure, making it challenging to detect and diagnose. 

It has optic nerve damage and visual field loss, and it may not present noticeable symptoms until it’s in advanced stages. 

Regular eye check-ups are vital for early detection of NTG.

Treatment for NTG primarily focuses on lowering eye pressure through prescription eye drops, laser treatments, or, in some cases, surgery. 

There are some non-eye pressure factors, such as blood pressure patterns, diet, exercise, meditation, and smoking, to manage the Normal-Tension Glaucoma.

With early detection and appropriate treatment, protecting your vision and maintaining eye health is possible.

Frequently Asked Questions

What is the cause of Normal-Tension Glaucoma?

The exact cause of NTG is not fully understood, but it’s believed to involve a combination of factors, including genetics, vascular issues, and possibly abnormal pressure inside the eye. Unlike other forms of Glaucoma, NTG occurs with normal eye pressure.

When can you get Normal-Tension Glaucoma?

NTG can affect people of various ages, but it’s more common in older individuals. It typically becomes more prevalent as people get older, with a higher risk after age 40.

What is the best treatment for Normal-Tension Glaucoma?

The primary treatment for NTG is to lower intraocular pressure (IOP), reducing the risk of vision loss. This is usually achieved through eye drops, laser therapy (such as selective laser trabeculoplasty or SLT), or surgery in some cases.

Who is at risk of NTG?

Several factors increase the risk of NTG, including age, family history of Glaucoma, certain medical conditions like high blood pressure, and specific optic nerve characteristics. People with a family history of NTG are also at a higher risk, which can affect both men and women.

Citations:
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