Chat Highlights
Normal-Tension Glaucoma Research
May 16, 2001

Norma Devine, Editor

On Wednesday, May 16, 2001, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Normal-Tension Glaucoma Research." 

Moderator:  The topic tonight is normal-tension glaucoma research.

P:  How are normal-tension glaucoma (NTG) and lower blood pressure/blood flow related?  Wouldn't raising blood pressure raise the IOP (intraocular pressure) as well?

Dr. Rick Wilson:  No.  The healthy eye auto-regulates its own blood flow according to the needs of the eye.  A sudden rise in blood pressure will raise the eye pressure for just a short while before it adjusts the IOP down.  Too low a blood pressure may be hard to adjust for if there is cholesterol build-up in the vessels leading to the eye or spasms of the vessels, such as seen in those with migraines.

P:   Migraines of the eye or head?

Dr. Rick Wilson:  Migraine sufferers usually have a systemic problem characterized by spasm of the vessels in the brain, which causes the pain.  They are also prone to spasms elsewhere. 

P:   I don't understand.   Are you saying that raising the blood pressure is good long term or not?

Dr. Rick Wilson:  Raising blood pressure from too low to normal is good for NTG.  Raising it to supra normal levels will improve blood flow to the eye for a short while.  But then changes to the vessels themselves will occur that will limit blood flow again in a pathologic way.

P:  It appears that I am among the 12% of glaucoma patients who does not respond to treatment.  Although I have successfully lowered my IOP more than the recommended 30%, my visual field loss is progressing unabated.  Research on perfusion to the optic nerve interests me.

Dr. Rick Wilson:  Some people have to lower IOP 40% or more.  Most damage stops once IOPs are down to 12 mm Hg. or below. In my experience with the few patients getting worse at 12, their damage stopped once I got the IOP down  to 8. 

P:  The damage stopped for how long?

Dr. Rick Wilson:  For as long as I kept the IOP there. 

P:   Is there any  current treatment that is promising for NTG?

Dr. Rick Wilson:  Yes.  If the people in the White House will allow research in stem cells gathered from unused embryos from fertility clinics, as well as other sources, we may be able to regenerate optic nerve tissue within the next 10 years.  There is also plenty of research on neuroprotection now.  This is aimed not just at lowering IOP but also at protecting the nerve cells in the retina (the retina ganglion cells) that are injured in glaucoma by a variety of means.

P:  Is there any test to see if  the optic nerve is getting enough blood?  

Dr. Rick Wilson:  We have color Doppler and laser scanning ophthalmoscopes to judge blood flow to the eye and into the eye.  These techniques are not quite as sophisticated as we would want, but they are getting close.  

P:  Am I right that the blood pressure to the optic nerve is thought to be typically about 14 mm Hg,  so the target pressure is below 14, or below 12,  as you mentioned?

Dr. Rick Wilson:  No.  The blood pressure in the central retinal artery is much higher than that, otherwise when a patient had a rise in IOP to 50, there would be no blood coming into the eye.  However, cholesterol buildup in the vessels leading up to the eye, spasm of those same vessels, low systemic blood pressure, etc., can reduce the blood pressure to dangerously low levels.

Moderator:   What can you tell us about the big NTG study?  

Dr. Rick Wilson:  The study showed that lowering IOP 30% will slow or stop the damage in most, but not all, NTG patients.  Not all untreated patients got worse. Patients with IOP lowered surgically were prone to earlier cataract formation.

P:  What about using umbilical-cord blood or umbilical cords instead of embryos?

Dr. Rick Wilson:  Using cord blood has been quite successful, but those cells have already differentiated into blood cells.  It is much easier to get cells that have not already differentiated to turn into the type of cells needed.  

P:  Is stem cell research being conducted overseas?

Dr. Rick Wilson:  Yes, England is quite advanced in that field.

P:  Could you comment on the notion that certain types of  glaucoma, such as pigmentary,  may resolve on their own and can be misdiagnosed as NTG.  

Dr. Rick Wilson:  That is a possibility.  Inflammatory, traumatic, and steroid-induced glaucoma cause nerve damage that could be mistaken for NTG.

P:  How does one find out about studies like the one mentioned earlier?  

Dr. Rick Wilson:  The big one was run by the National Eye Institute of the NIH (National Institute of  Health). Looking on their website might turn up mention of the various, current studies.  If  they are not listed, you could call and ask which was the closest participating center.  

P:  Since many  NTG patients are myopic, is it possible that the elongated shape of our eyeballs causes that restriction in blood flow?

Dr. Rick Wilson:  Possibly, but it is more likely related to the diminished support given to the optic nerve by the thinner support tissue around the optic nerve.

P:  I  wonder why Drs. Drance and Anderson didn't realize when they started the big NTG study that it would take five years for the control group to start to show progression. Why, with all their years of experience, do you think they didn't know that? 

Dr. Rick Wilson:  I don't know the answer to that one. 

P:  While we're waiting, what was their definition of progression in that study?

P:  When at least two adjacent points on the visual field test dropped at least 10 db.

P:   Is it more difficult to treat NTG than glaucoma that has elevated pressure?

Dr. Rick Wilson:  Yes.  It is much easier to lower IOP 30% when the IOP is 45 than when it is 15.

P:  There is some debate about the term "low-tension glaucoma" (LTG) vs. "normal-tension glaucoma."  Is there a difference? 

Dr. Rick Wilson:  The correct term is normal-tension glaucoma,  since most NTG occurs with IOPs in the teens or normal range. NTG can occur in patients with IOPs less than 12, but it would be rare. Therefore,  LTG is not an accurate descriptive term.

P:  But is LTG  a separate condition?  My doctor says the terms are interchangeable.

Dr. Rick Wilson:  NTG is really a wastebasket of syndromes that cause damage characteristic of glaucoma,  but may have one of many causative mechanisms.

P:  Has the possibility of patient non-compliance (not taking meds between office visits) ever been studied in relation to diagnosing NTG?

Dr. Rick Wilson:  It has been and continues to be studied.  However, I don't know of a study, off-hand, that looks just at NTG patients.  

P:  If there is patient non-compliance, wouldn't that lead the doctors (through no fault of their own) to diagnose NTG if the IOPs are always normal in the office?  So in the NTG studies, are the drops counted routinely?

Dr. Rick Wilson:  Unfortunately, no.  

P:  Is there any other glaucoma research going on outside the U.S. that could be worthwhile for those who can travel?

Dr. Rick Wilson:  Not that seems ready for patient care yet.  It may be coming soon to a country near you.

P:  If in NTG there are many causative mechanisms, should there also be different treatments?  That is, besides lowering IOP, would potentially neuroprotective agents or antioxidants be appropriate for NTG patients?  

Dr. Rick Wilson:  Yes.  We should be approaching nerve loss from a variety of ways. Lowering IOP is just one of those ways. We should be improving circulation, making sure that there is no autoimmune component,  and supplying growth factors and other essential factors to the retinal ganglion cells, as well as suppressing the production of injurious chemicals.

P:  I have read that in Great Britain trabeculectomies are performed early in glaucoma treatment, because the government medical system thinks that surgery is more cost-effective than long-term medication.

Dr. Rick Wilson:  That is true, but I hope it's because the government and the specialists agreed that it is best for the patient.

P:  What growth factors affect the retinal ganglion cells? Can they be obtained nutritionally?

Dr. Rick Wilson:  Perhaps they may be increased nutritionally once we understand what they are and what they are doing.

End of chat highlights for May 16, 2001.

On May 23rd, Dr. Wilson discussed "How Aqueous Humor Flows" in the Chat room. Click here for highlights of that meeting.

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