2.5 years ago

Dave deBronkart • 70

@deb

A relative has been diagnosed with "normal pressure" glaucoma aka "normal tension" glaucoma. This makes no sense to us, since our understanding is that glaucoma IS high eye pressure, which can kill nerves, eventually causing blindness. What are we missing or not understanding??

She asked her docs but hasn't been able to get an answer that makes sense. And all the websites we've searched are either way too technical or way too vague, e.g. "But sometimes glaucoma can happen when pressure is not elevated" with no more information.

3.0 years ago

david 4.3k

@david_fe

our understanding is that glaucoma IS high eye pressure

Maybe that is the source of some confusion. Glaucoma is not equal to elevated eye pressure (intraocular pressure). Technically, elevated intraocular pressure is just a risk factor for glaucoma.

Elevated intraocular pressure (IOP) is the most important risk factor because it is the only medically treatable risk factor at this time.

Many years ago, Dr. Robert Ritch shared this important understanding of glaucoma with the FitEyes community:

All glaucomas have a final common pathway of retinal ganglion cell death involving low-grade inflammation, oxidative damage, mitochondrial dysfunction, and glial hyperactivation.

You could say that is "glaucoma in one sentence."

Notice that elevated eye pressure is not part of that sentence. That's as it should be because glaucoma does not equal elevated eye pressure, as I said above. Elevated eye pressure is just one risk factor.

Therefore, it is not an oxymoron to speak about normal tension glaucoma (or even low tension glaucoma).

That probably answers the question for many readers. Stop reading here if you feel satisfied. However, a deeper exploration of the question continues below the fold.

Today, medical science does not know exactly what causes glaucoma. We know that there are many factors that contribute to it, and that some of these factors are more important for some individuals. Without understanding the root cause, and by virtue of the fact that there are many variants of the optic neuropathy we call glaucoma, defining glaucoma is difficult. Therefore, defining normal tension glaucoma will entail challenges.

There are around thirty factors that contribute to glaucoma, from genes to systemic inflammation to mitochondrial dysfunction. Elevated IOP is the most important factor for many people living with glaucoma, but others have glaucoma without elevated IOP -- which is the point of this question.

I need to say that IOP remains the most important treatable risk factor even for people with normal- or low-tension glaucoma. Many people with NTG rightly feel dissatisfied with that state of affairs, but our best science hasn't yet given us better treatment options. However, many patients with NTG want to see more research attention focused on other factors, and they often focus their own lifestyle approaches on factors such as inflammation, blood flow to the eye, etc.

In this spirit, I want to mention one other major theory about a fundamental cause of glaucoma -- mechanical stress on the optic nerve where it exits the back of the eye. That topic is highly relevant to NTG.

The optic nerve exits the back of the eye through a structure called the lamina cribrosa. It is the boundary between two systems. There are two opposing pressures pushing on each side of it.

On one side of the lamina cribrosa is IOP (what we commonly call eye pressure). On the other is the cerebral spinal fluid pressure ("CSFP" or "CSF pressure"). The difference between those two pressures is more important than the absolute value of either one (except possibly in extremes). This is a key factor in understanding normal tension glaucoma.

If a person has an elevated IOP of 30 and a similarly elevated CSFP they would have balanced pressures at the lamina cribrosa and may not experience glaucoma -- even with elevated IOP.

Likewise, a person with normal IOP but below normal CSFP would have a pressure imbalance at the lamina cribrosa and may experience glaucoma -- even with normal or low IOP.

Side bar:

CSFP measured at the base of the spine and with the patient lying on the side is normally 8-15 mmHg. That rises to 16–24 mmHg when we sit up. As you see, CSFP is in the physiological range of IOP.

The pressure imbalance (between IOP and CSFP) puts mechanical stress on the optic nerve. That's bad for the nerve.

Some studies have confirmed that glaucoma patients with normal intraocular pressure glaucoma have significantly lower CSFP and a higher trans-lamina-cribrosa pressure difference when compared to normal subjects.

But this topic gets a bit complicated. For example, CSFP behind the eye may not be equal to CFSP at the base of the spine due to compartmentalization. Measuring absolute CSFP directly behind the eye is not easy. It is also not routinely done.

3.0 years ago

FitEyes Team 260

@fiteyes_team

Dr. Robert Ritch says:

NTG (normal tension glaucoma) is just glaucoma where the IOP is not high.

With IOP in the low 20’s, you can have a mixture of both (NTG and POAG)

3.0 years ago

Sherry • 70

@sherry

I have NTG. My eye pressure is 17 without any eyedrop.

NTG accounts for more than half of the glaucoma patients in Japan. Contrary to what research said in US, 5% of Japanese have glaucoma, which is much higher than the common belief that African-American have higher risk of glaucoma (a simple google search can prove it but US media just didn’t count in Asians).

NTG Usually have eye pressure lower than 21. I have some glaucoma friends who have eye pleasure of 15 but still developed glaucoma. NTG usually progressed slower.

The treatment of NTG is same as that of other glaucoma patients by using eyedrops to lower pressure. NTGs usually have blood circulation issues and low blood pressure

3.0 years ago

EyeTidbits • 70

@eyetidbits

To answer the original question in perhaps a less technical way, glaucoma is basically defined as having damage to the optic nerve, which can lead to blindspots & blindness. In most glaucoma patients (POAG), the optic nerve damage is correlated with high eye pressures. In normal tension glaucoma (NTG) patients, however, there is optic nerve damage even though eye pressures are “normal.” High eye pressure has been considered the main cause of optic nerve damage, but there are other possible causes, for example, poor blood circulation to the optic nerve (low perfusion). Stress, inflammation, nutritional deficiencies, & toxicities are other possible factors. Also, a more correct term for NTG is LTG (low tension glaucoma), because what is “normal” pressure for some people may be actually too high in NTG patients, thus causing damage (which is why the goal in NTG is to lower the eye pressures below “normal”). That is why some glaucoma specialists prefer to use the term LTG rather than NTG. Commonly, the goal in NTG is to lower the pressure by 30%. So if one’s pressure at diagnosis is 16, the goal in therapy is to aim for 11. In a nutshell, the eye pressures in NTG (LTG) patients, though “normal,” are too high for them individually, resulting in optic nerve damage if ignored.

3.0 years ago

christineQuinn • 0

@christinequinn

Glaucoma is a multi-faceted condition characterized by progressive optic neuropathy and visual field loss that may or may not is linked to an increase in intraocular pressure. The normal intraocular pressure for most people is between 10 and 20 mm Hg, however, there are always exceptions. As a result, there is a kind of glaucoma known as Normotensive Glaucoma, which causes visual abnormalities and optic neuropathy even when the pressure is within this range or lower.

3.0 years ago

Dave deBronkart • 70

@deb

Thanks to Robert Cohen on Discuss for posting this:

A new article just came out in the Journal of Glaucoma in November: Multiple Systemic Vascular Risk Factors are Associated with Low Tension Glaucoma It was a retrospective study of 277 cases, which is a relatively weak form of research, but it's a legitimate thing to do when you're first exploring a new idea.

Bottom line, it said numerous vascular factors were associated with LTG (low tension glaucoma), which is in stark contrast to the idea that IOP is the only thing that matters. Specifically, all these factors had correlations, and most of them are vascular!

• Myopia (p<0.001, very strong correlation)
• higher cup-to-disc ratio, P<0.001)
• diabetes (P<0.001)
• anemia (P=0.003)
• high blood pressure (P=0.004)
• peripheral vascular disease (P=0.009)
• migraine headache (P=0.02) (migraines are triggered by vasospasm)
• less likely to have BMI >30 (P<0.03, not hugely strong)
• low blood pressure (P=0.03)
• Raynaud's disease (P=0.05, not terribly strong)