Normal-tension Glaucoma
Chat Highlights
January 2, 2002

Norma Devine, Editor

On Wednesday, January 2, 2002, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Normal-tension Glaucoma."

Moderator:  The topic tonight is normal-tension glaucoma (NTG).  Are there any questions? 

P:  Is normal tension glaucoma a subset of open-angle glaucoma?

Dr. Rick Wilson:  That's hard to answer.  The damage in NTG produces the same appearance as POAG (primary open-angle glaucoma), but there are slight differences in the appearance of the optic nerve and the visual field.  It is also a disease mostly of the elderly, except for some 45- to 55-year-old women I see with chronic, very low blood pressure. 

P:  What causes NTG?

Dr. Rick Wilson:  Normal-tension glaucoma seems to be a wastebasket term for a bunch of conditions -- many of which we don't know -- that all sensitize the optic nerve to damage at normal pressure.  The known ones include low blood pressure (sometimes only in the early morning hours), autoimmune disease, thick blood, anemia, heart arrythmia, etc.  Sleep apnea is getting increasing attention as a possible cause of NTG.

P:  I know what you mean about thick blood.  After I had a pint of blood removed every week for six months because of too much iron in the blood, my IOP went down because the blood became thinner.  

Dr. Rick Wilson:  The greater problem with thick blood is that it has a harder time getting through the small blood vessels in the optic nerve to nourish it, especially if the IOP is at all higher than normal.

P:  Do most patients get NTG genetically?  

Dr. Rick Wilson:  I don't think so.  My father, at age 80, was the first one in his family to develop NTG.  

P:  If one suffers damage at a pressure of 19 mm Hg, is that considered NTG?

Dr. Rick Wilson:  Yes.  

P:  Is the diagnosis still NTG if a patient with high IOP has suffered optic nerve damage, the pressure has been decreased to the normal range, but the damage progresses?

Dr. Rick Wilson:  That would normally be called POAG, with normal-tension progression.  That is actually quite common, if the POAG has resulted in serious damage to the optic nerve. The nerve seems to be "softened up" and then suffers damage in the normal IOP range.

P:  In such cases, do you think glutamate excitotoxicity accounts for this "softening up" of the nerve, or some other mechanism?

Dr. Rick Wilson:  It could be a chemical like glutamate that is released by a dying nerve cell and causes injury to the surrounding nerve cells; or it could be the circulation is changed with the previous damage; or it probably is a link we haven't found yet.

P:  It seems NTG might provide a lot of clues about what causes damage to the optic nerve.  Has it taught glaucoma specialists anything new?  

Dr. Rick Wilson:  I think it is teaching us about the kinds of disorders that can cause injury to the optic nerve, and which of them look like glaucoma and which do not.

P:  I am thrilled that NTG is treatable with drops, but frustrated that no one really seems to be looking that hard to figure out why I got it.  How can I hope to be cured if we are just treating the symptoms?

Dr. Rick Wilson:  Lots of scientists are looking at the cause, but it is more difficult to discover the cause than it is to make advances in the treatment.

P:  Actually, there is no advantage knowing whether it is NTG or not since treatment is about the same, except that the pressure needs to be kept even lower for those with NTG.  Is that correct?

Dr. Rick Wilson:  Yes and no, since with NTG we usually investigate the causes I mentioned above, in case one of the sensitizing conditions might be treatable.  I have found patients with normal-tension glaucoma and serious heart irregularities who suffered no further damage after they had a pacemaker inserted.

P:  How long does it take to find the root cause, usually, when it can be found?  I sure wish someone was trying to find it in me.

Dr. Rick Wilson:  If it is one of the known causes, the condition can be found fairly quickly if looked for.

P:  How does the appearance of the visual field differ in patients with NTG and POAG?  

Dr. Rick Wilson:  Patients with NTG often have small, dense defects close to the center of vision. That is unusual with POAG until late in the course of the disease.

P:  What do you mean?  How late, or what are the signs?

Dr. Rick Wilson:  Dense loss of visual field usually appears in POAG 10 to 20 degrees from the center point of fixation of vision.  In NTG, the defects may be right on fixation or very close.

P:  I have NTG.  My visual field shows a loss almost entirely in the upper field.  You could draw a straight line across the middle of my eye.  The top part is blind, the bottom part is okay.  Is that a common loss for advanced NTG?

Dr. Rick Wilson:  Yes, and we don't know why one part of the retina or nerve would be so much more susceptible to glaucoma damage.

P:  Do you have any thoughts about the cause of  fragile optic nerves?  

Dr. Rick Wilson:  Good question.  Perhaps the support meshwork that holds up the optic nerve is weaker or has larger holes in it,  so the nerve is not as well supported in the face of increased IOP.

Moderator:  Is the damage seen in NTG different from that of narrow or closed-angle glaucoma?

Dr. Rick Wilson:  Yes.  Patients with angle-closure glaucoma often have high spikes in their IOP, up to the 40s to 60s for a short time.  This type of damage usually does not cause the cupping seen with POAG, but a pallor appears in the nerve over a month later that is indicative of the damage caused.

P:  It would seem that earlier treatment might help to avoid POAG with NT progression; but can that be achieved if treatment isn't given until damage begins?

Dr. Rick Wilson:  The earlier the damage is discovered,  the less chance there is of normal tension progression.

P:  Is NTG more or less likely to progress worse than regular POAG?

Dr. Rick Wilson:  Slightly more, but my dad had it for 16 years without much progression and many of my NTG patients are absolutely stable.  So it can be accomplished if the IOP is brought down far enough.

Moderator:  Could low blood pressure be damaging the optic nerve if the pressures are in the normal range?  

Dr. Rick Wilson:  Low blood pressure is damaging to the optic nerve if the blood pressure is not high enough to push blood into the eye to the optic nerve against the pressure of the fluid in the eye.  When you lie down, the IOP may go up a couple of points, which just exacerbates the problem at night.

P:  I keep hearing that low blood pressure can be a factor, yet few eye doctors take their patients' blood pressure.  So they must not really believe it.

P:  Some seem to take a careful medical history.  

Dr. Rick Wilson:  Or they depend on communication with the patient's medical doctor. 

P:  When you refer to low blood pressure, do you mean very low, perhaps as low as 90/50 mm Hg?  

Dr. Rick Wilson:  Or 80/45 mm Hg, etc.  

P:  Before I gave blood on Friday my blood pressure was 150/85 mm Hg, which is as high as mine has ever been.  Afterwards, the pressure was 118/58.  Is giving blood a bad idea for me?

Dr. Rick Wilson:  If you are a man, giving blood is a good idea if you are healthy.  There is one school of thought that too much iron is injurious to the heart.  Women, after years of menstruating, are rarely in that situation.  But men can be, and giving blood lowers the stored iron levels.

P:  Does a high hemoglobin reading indicate thick blood?  If so, how high?

Dr. Rick Wilson:  The more blood cells, the more hemoglobin.  The more cells there are in a given amount of blood, the thicker it is.

P:  My seven-year-old daughter has slight damage to her optic nerve (between two and three on the progression chart.)  The optometrist wasn't concerned.  Her pressures were 20 and 22 mm Hg. with the air-puff test.  She also has a slightly lazy eye.  Could my NTG be hereditary?  Should I make an an appointment for her with my specialist?

Dr. Rick Wilson:  Yes.  A seven-year-old should have an IOP in the low teens.  The puff test is inaccurate.  She should not be seeing an optometrist if there is a question of glaucoma, since optometrists do not see enough children with borderline pressures to be experienced enough.

P:  Are optometrists generally competent to spot glaucoma damage?

Dr. Rick Wilson:  That's a loaded question.  Some are; many are not.  It depends upon their training and how long ago they had the training.

P:  Doctor Rick, I get more questions answered here than at my doctor's office, because he is always in such a hurry.  Too many patients and not enough time.  Thank you very much for all your help and the time you give us.

Dr. Rick Wilson:  You're welcome.  Good night, everyone.  Happy New Year!

End of highlights for January 2, 2002.

On January 9, Dr. Wilson discussed "Glaucoma Awareness" in the Chat room. Click here for highlights of that meeting.

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