What is Normal-Tension Glaucoma?
Chat Highlights
March 30, 2005

On Wednesday, March 30, 2005, Dr. Elliot Werner and the glaucoma chat group discussed "What is Normal-Tension Glaucoma?"

Moderator:  Welcome back, Dr. Werner. The topic tonight is "What is Normal-Tension Glaucoma?"

Dr. Elliot Werner:  We think of glaucoma as an optic nerve disease that produces a characteristic change in the optic nerve, which we call cupping.  We make the diagnosis based on the typical appearance of the optic nerve and the typical effects on visual function (mostly the visual field.)  Most cases of glaucoma are associated with elevated intraocular pressure (IOP).  It is the pressure of the fluid in the eye that seems to produce the damage to the nerve.  Many patients, however, develop glaucoma that we can detect in the optic nerve without having an elevated eye pressure. These patients are said to have normal-tension glaucoma (NTG), but most people believe NTG is not fundamentally different from other forms of high-pressure glaucoma.

P:  How do you make the diagnosis of NTG?

Dr. Elliot Werner:  The diagnosis is made the same way as for other forms of glaucoma.  The optic nerve is examined and characteristic signs of cupping are seen associated with typical areas of loss in the visual field that are also characteristic of glaucoma.

P:  Which NTG patients should be treated?

Dr. Elliot Werner:  Those with extensive damage, younger patients, and those showing progression.  Also, those with IOP in the upper range of normal.

P:  Is NTG more prevalent in one gender, age group, or race?

Dr. Elliot Werner:  NTG is more prevalent in older individuals.  Like ordinary open-angle glaucoma, the frequency of NTG increases significantly with age.  NTG seems to be more prevalent in Asian populations for reasons that are not clear.

P:  What is the usual treatment for NTG?

Dr. Elliot Werner:  Most studies have shown the treatment of NTG is much the same as for other forms of glaucoma.  The pressure is lowered as much as possible without harming the patient with the treatment.  The usual modalities of drops, laser, and surgery are used, depending upon the patient's clinical course.

P:  Is it feasible or helpful to use medications to attempt to lower pressure below 12 or 13 mm Hg when damage is evident?

Dr. Elliot Werner:  It is certainly worth a try, but it is very difficult to be able to lower the IOP below 12 or 13 mm Hg with medication alone.  Studies have found that about half of NTG patients will require surgery to produce an IOP drop of greater than 30% or so.

P:  Can a doctor be pretty sure that glaucoma is going to progress to further damage if the IOP is not reduced?

Dr. Elliot Werner:  No.  It is very difficult to predict those in whom glaucoma will progress and those in whom it will not.  The best we can do is assign probabilities based on risk factors.

P:  Is it true that progression in NTG is either very slow or occurs in rather small increments?

Dr. Elliot Werner:  Like most forms of glaucoma, it is highly variable from patient to patient.  About half of NTG patients don't seem to progress at all for long periods.  Others progress slowly. Some progress fairly rapidly, although rapid progression is not the usual course of NTG.

P:  Is it harder to prevent progression in NTG than in chronic open angle or other types of glaucoma?

Dr. Elliot Werner:  Actually, no.  The progression rates seem about the same.  Some studies, in fact, have shown that rapid progression is less likely in patients with lower eye pressures.

P:  Does the IOP in NTG start in the 20 to 22 mm Hg range, or do you see it in eyes with pressures that never get that high?

Dr. Elliot Werner:  Most patient with NTG have pressures in the 17-21 mm Hg range, but some are also seen with very low pressures.  Many eyes never have pressures higher than 16 mm Hg or so.

P:  How often does NTG become glaucoma with elevated IOP?  And can the IOPs decrease with no treatment, but the damage continues to progress?

Dr. Elliot Werner:  NTG doesn't become high-pressure glaucoma.  Glaucoma is glaucoma, and in glaucoma the eye pressure may fluctuate or increase as the patient ages.  In that case, it may appear that NTG has changed into high-pressure glaucoma, but all you are seeing is the natural history of the disease.

P:  In such a case, is the glaucoma still called NTG?

Dr. Elliot Werner:  It is unfortunate that the term NTG even exists, because it tends to lead people to believe that this is a separate disease entity.  Some of the questions tonight already betray that mindset.  NTG is not another disease.  It is the same as open-angle glaucoma, but with an IOP in the statistically "normal" range.

Moderator:  Is here a difference in frequency by gender?

Dr. Elliot Werner:  Not as far as we know.  Studies have not given consistent results on this question.  Women tend to live longer so it may appear more prevalent in them, but that is probably age-related.

P:  My impression from reading about NTG is that vascular factors are suspected to play a larger role in NTG, presumably to a greater extent than in high-pressure glaucoma; that even in the absence of a presumptive anatomical insult to the nerve at the lamina cribrosa, there is some fundamental vascular insufficiency.  Is that an accurate perception?

Dr. Elliot Werner:  Again, the studies give inconsistent results.  My reading of the literature and my opinion is that there is no good hard evidence for a significant vascular factor in NTG, as opposed to glaucoma with higher pressures.

P:  Some of us (including me) have unilateral damage (one eye only), and no progression so far.  The big question for us is whether we have NTG or have had an ischemic incident of some sort. In my case, the answer may be easier, because the damage is in the eye with a slightly lower pressure than the other, and there are precipitating factors.  But for those whose loss is in the eye with the higher pressure and who cannot attribute the loss to anything, do you wait for progression before treating?  If so, how long, generally, does it take for progression to show up?

Dr. Elliot Werner:  Stable damage in one eye would suggest a diagnosis other than glaucoma, but that is often difficult to prove.  In patients with early NTG, especially older individuals, many clinicians will wait for progression before treating. In more advanced disease, most clinicians would treat immediately.  Studies have shown that over a 5- to 10-year period about 50% of NTG patients show progression.

P:  I'm a white male, 58 years old, with NTG.  Due to damage to the optic nerve, I had SLT (selective laser trabeculoplasty) in my right eye on January 6 of this year.  A month later there was no drop in pressure, and only a moderate drop (from 17 to 14 mm Hg) after two months.  What is the likelihood that I will need a trabeculectomy?

Dr. Elliot Werner:  Depending on the amount of optic nerve damage, a drop in IOP from 17 to 14 mm Hg may be quite adequate.  I would follow a patient like you for a good long time before recommending filtering surgery.

P:  In a study by Douglas Anderson, M.D. et al, (Bascom Palmer Eye Institute, Miami) researchers found that 30% of patients with NTG also had other autoimmune diseases, whereas in the control population, only 8% of individuals had other autoimmune diseases.

Dr. Elliot Werner:  That is true and interesting.  Others have found similar results.  The exact significance of those findings is unclear.  Also, those were relatively small, clinic-based studies from referral centers and may not be representative of the population at large.

P:  What are the chances that in my case NTG glaucoma damage was caused by a nasty fall on my forehead (I fell off my granddaughter's scooter coming downhill) last September.  I had 12 stitches in the left eyebrow, and later a subdural hematoma.  [Note: a subdural hematoma is a collection of blood on the surface of the brain.]  My IOPs are 12 and 13 mm Hg.  My glaucoma specialist says both optical discs are damaged, and my visual field test results are poor in both eyes.  Could wearing disposable contacts be causing high IOP in the daytime that doesn't show up when I take them off for my visit with my doctor?

Dr. Elliot Werner:  As far as we know, head injuries do not cause NTG.  It is unlikely your NTG is related.  The type of injury you had, however, can also damage the optic nerve and produce a picture that may resemble glaucoma.  In your case, it would need to be determined if your optic nerve damage was due to your injury or to glaucoma.

P:  Why would optic-nerve damage continue in a patient with POAG (primary open-angle glaucoma) whose initial pressures were in the 40 mm Hg-range, but after surgery and using eyedrops the patient now has pressures around 16 mm Hg?  Would lowering the pressure to 13 mm Hg or less make any difference if progression is continuing at a normal pressure?

Dr. Elliot Werner:  No one knows the answer to your question, but it is a common and very troubling problem.  Many glaucoma patients with damage seem to progress despite what appears to be adequate pressure lowering.  We believe that lowering pressure in such patients even more may help halt or slow the progression, but there is no good proof of that.

P:  My friends keep suggesting nutritional supplements.  Is there any solid evidence that vitamins and minerals help with POAG and NTG?

Dr. Elliot Werner:  There is some evidence that gingko biloba helps stabilize the optic nerve.  There is no other good scientific evidence for any other nutritional supplement, but good nutrition is always a good idea and certainly promotes good health.

P:  You can have more than one autoimmune illness, such as Raynaud's and rheumatoid arthritis, but in some patients couldn't the only manifestation of autoimmune disease be normal-tension glaucoma?

Dr. Elliot Werner:  There is no evidence that NTG is an autoimmune disease or even a manifestation of an autoimmune disease.  All that has been shown is a possible association with autoimmune disease, but an association doesn't prove cause and effect.

P:  I am 57 years old and have been treated for NTG for three years.  Recently, my 21-year-old son had an eye exam and took a visual field test.  He has shown some loss of vision and is now on drops.  Other than monitoring him closely, what else should be done?  Is there any value for him in genetic testing?

Dr. Elliot Werner:  Unfortunately, although we believe glaucoma is hereditary in cases like yours, in most cases we cannot identify a specific gene.  There are people who do family and genetic studies on glaucoma.  I cannot recall who or where off the top of my head.

P:  Dr. Paul Lichter at the University of Michigan does such studies.  The phone number is 1-888-EYE-GENE.  [Editor's note: See "Treatment and Genetic Studies of Glaucoma, Research Studies." http://www.kellogg.umich.edu/bios/lichter.research.html]

P:  I understand that certain actions, such as headstands, can raise IOP.  Is that true for everyone, or is there some resistance to any pressure change upward in NTG patients?

Dr. Elliot Werner:  Putting the head lower than the heart always raises the IOP in everybody, due to the increase in the blood pressure in the head.  In fact, there are many cases reported of people developing optic nerve damage who spend a lot of time in an upside-down position.

P:  Have you seen many cases in which NTG becomes PSXF (pseudoexfoliation) glaucoma as the years go by?

Dr. Elliot Werner:  I haven't observed that, but it has been reported.  But, again, it is misleading to think of one disease "becoming" another.

On April 6, 2005, Dr. Wilson discussed "Who Gets Glaucoma and Why?" in the Chat room. Click here for highlights of that meeting.

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