Chat Highlights
Normal-tension Glaucoma
August 29, 2001

Norma Devine, Editor

On Wednesday, August 29, 2001, Dr. Elliot Werner, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Normal-tension Glaucoma." 

Moderator:  Tonight the topic is "Normal-tension Glaucoma ."  Dr. Elliot Werner is our guest.   Dr. Werner is a glaucoma specialist at Wills.  He will be here the last Wednesday of every month, starting tonight. Welcome back, Doctor Werner.

Dr. Elliot Werner:  Thank you.  I am not the world's fastest typist, so be patient.

P:  Doctor Werner,  I'm a normal 41-one-year-old woman.  Why would I have normal-tension glaucoma (NTG?)

Dr. Elliot Werner:  Most NTG in younger patients is genetic in origin. Do you have a family history of glaucoma?

P:  No.  

Dr. Elliot Werner:  Remember, NTG is probably not a different disease from the garden variety open-angle glaucoma.  Most of these are probably genetic in origin.  As glaucomas go, NTG is actually a relatively benign condition.  Blindness is unusual in NTG, but that is not much comfort to those who have significant vision loss from the disease.

P:  In what way is NTG relatively benign compared to POAG (primary open-angle) glaucoma?  It seems harder to treat.

Dr. Elliot Werner:  NTG is more difficult to treat in the sense that it is more difficult to lower the IOP.  It is more benign in the sense that blindness is less likely to occur.

Moderator:  The next question is from a busy mother of two, who could not be here tonight:  "I have normal tension glaucoma.  My visual field tests show loss in my central vision.  I thought glaucoma robbed people of their peripheral vision first.  Why would this occur with NTG?  Is this uncommon?"

Dr. Elliot Werner:  Loss of central vision is unusual in early glaucoma, but common as the disease progresses.  Whether or not this woman's loss of central vision is remarkable depends upon how advanced her optic nerve damage is.

P:  Is loss of vision close to fixation common in NTG?

Dr. Elliot Werner:  The evidence for loss of vision close to fixation is statistical only.  It is more common in NTG, but it is not characteristic. 

P:  Is there a connection between chronically low blood pressure and NTG?

Dr. Elliot Werner:  There is some association between chronically low blood pressure and NTG.  

Moderator:  What percentage of NTG patients have chronically low blood pressure? 

Dr. Elliot Werner:  I'm not sure, but probably a significant minority have some abnormality of blood pressure on the low side.  The blood pressure of many people drops when they sleep, and that may have an association with NTG.  

P:  If an NTG patient has mildly elevated blood pressure and is being prescribed medication to lower it, wouldn't a calcium channel blocker be a good alternative to a diuretic?

Dr. Elliot Werner:   I wouldn't comment on treatment of  blood pressure, but the use of calcium channel blockers is a double- edged sword, since they can drop the blood pressure too low in some people with NTG and make it worse.  

P:  Do about half of glaucoma patients have NTG?  

Dr. Elliot Werner:  Probably closer to about 1/4 to 1/3 of glaucoma patients have NTG. 

P:  Is it more difficult to control NTG, since pressures are already "normal"? 

Dr. Elliot Werner:  Most patients with NTG do not show significant progressive visual loss over many years, and often do not need any treatment at all.

Moderator:  Could optic nerve damage in NTG patients be caused by something other than IOP?  

Dr. Elliot Werner:  Most recent evidence from the NTG Collaborative Treatment Trial and studies involving patients with asymmetric NTG show that IOP is still the main, but certainly not the the only, factor producing damage.  The other factors are largely unknown at present.   The NTG treatment trial showed that about two-thirds of NTG patients do not progress after five years of follow-up, so probably about two-thirds do not need treatment.  

P:  Might those patients just have a very slow rate of progression?

Dr. Elliot Werner:  Of the NTG patients who do progress, I don't know of any evidence they progress more slowly.  Rates of progression are highly variable in all forms of glaucoma.

Moderator:  I don't understand.  NTG patients must have optic nerve damage.  Does the damage stop? 

Dr. Elliot Werner:  It either stops after a while, or it progresses so slowly that it is not clinically detectable for long periods of time.

P:  If two-thirds of NTG patients don't show progression, isn't that the same as saying they've been misdiagnosed?

Dr. Elliot Werner:  The two-thirds who did not progress in the treatment trial were almost certainly correctly diagnosed.

P:  I didn't mean that the two-thirds who did not progress did not have glaucoma, but that at some point in the past it may have been high-tension glaucoma, e.g., pigmentary dispersion.

Dr. Elliot Werner:  That's possible, but is usually ruled out during the work-up of the patient. 

P:  I have heard that some NTG patients are misdiagnosed and might have papillorenal syndrome, a genetic disease.  Can you tell us more?

Dr. Elliot Werner:  Some patients with diseases other than glaucoma may be misdiagnosed as having NTG.  That should be uncommon in the hands of a good clinician, because glaucoma usually looks like glaucoma.  If it doesn't look like glaucoma, you need to look for another diagnosis.

P:  So it seems that NTG, far from being the "bad" glaucoma, is better than some of the other kinds?

Dr. Elliot Werner:  All glaucoma is bad.  Some are worse than others.  Most patients with NTG  do fairly well, but some do terribly. 

P:  NTG is the most common form of glaucoma in Japan.  Do you  know if the Japanese have any different treatment regimes or any long-term studies on progression?

Dr. Elliot Werner:  There are many NTG studies out of Japan.  In Japan, there tends to be less use of surgery and more systemic treatment, such as calcium channel blockers.

P:  What is the theory about why the Japanese have a high percentage of  NTG patients? 

Dr. Elliot Werner:  Nobody knows why NTG is more common in Asian populations.

P:  Do you find that most patients with NTG are nearsighted or farsighted?

Dr. Elliot Werner:  Nearsightedness is more common in NTG and POAG, and is a significant risk factor for glaucoma.  There are five significant risk factors for glaucoma:  IOP, age, race, nearsightedness, and family history.

P:  I hear that one of the treatments to be studied for glaucoma is supplying growth factors to the retinal ganglion nerves.  What might some of those factors be?

Dr. Elliot Werner:  I am not an expert on growth factors.  These are proteins that are found in the body that support and nourish cells.  There is nothing I know of anywhere near human trials.

P:  My father was diagnosed with NTG in  1969, and was nearly blind when he died in 1997.  My grandfather was also blind when he died, though there was no doctor or diagnosis involved in his case.  My oldest sister was diagnosed with NTG, and has severe vision loss in her right eye, even after experimental surgery.  It seems that blindness in my family is a factor.  Can you comment on that? 

Dr. Elliot Werner:  Family history and genetics play a major role in the occurrence and course of NTG.  Your family must carry a gene for a particularly virulent type.

P:  Is the initial loss shown on the visual field tests of NTG patients different from the loss shown on the tests of POAG patients?

Dr. Elliot Werner:  The initial loss of visual field in NTG is not really different, but on average tends to be more localized and closer to fixation than in POAG.  

P:  Is there a possible connection between auto-immune conditions or circulation problems that result in a loss of blood perfusion to the eyes and the diagnosis of NTG?

Dr. Elliot Werner:  There is some experimental evidence that immune system abnormalities are associated with NTG, but there are no large population studies and no data that would affect  treatment. 

P:  How about circulation?

Dr. Elliot Werner:  There is some evidence that blood flow to the eye may be less in NTG than in normals, but the same is true of POAG, and the significance of that is unknown.

P:  What do you suggest when a patient is successfully lowering IOP to the single digits, but vision loss continues unabated?

Dr. Elliot Werner:  This is unfortunately very common.  Many patients with advanced disease continue to deteriorate despite very low IOP.  Not much can be done, and no treatment has been shown to be safe and beneficial. 

P:  Some researchers suggest that the problem in NTG lies at the level of the optic nerve, not in the trabecular meshwork.  

Dr. Elliot Werner:  The studies in the journals tend to disagree.  

Moderator:  Are there studies of why some glaucoma patients get worse even with low IOPs?  

Dr. Elliot Werner:  Yes, there's a lot of research concerning mechanisms of nerve damage in glaucoma  -- neuroprotection, glutamate, nitric oxide, free radicals.  There's a lot of basic science research, but nothing therapeutic yet. 

P:  I'm going blind (quickly) for a reason; and it's definitely not my IOP, which has never been higher than 16 mm Hg. 

Dr. Elliot Werner:  You represent one of the great tragedies of glaucoma practice.  You are going blind for a reason, but we don't know enough to figure out the reason.

P:  If NTG field losses aren't that much different from field losses in open-angle glaucoma,  does that mean the appearance of the optic nerve in NTG isn't much different from that of open-angle glaucoma either?  And if so, how can the diagnosis of  NTG be made without the patient having been followed before the diagnosis of  NTG?  

Dr. Elliot Werner:  I rarely use the term "normal-tension glaucoma" for that reason.  I think of open-angle glaucoma as a single diagnosis, regardless of the level of IOP. 

P:  In my case of NTG, I am working on a layman's theory about my extreme myopia.  My ocular length is much longer than normal, with a very thin retina.  According to the theory, my eyes have outgrown the circulatory support.  Treatment would be anything that keeps IOP low and increases blood flow, such as Cosopt, ginkgo biloba, exercise, etc.  

Dr. Elliot Werner:  All of those can be tried.  Sometimes they work; sometimes they don't.

P:  Either we try these things or just wait to go blind.

Dr. Elliot Werner:  You can try anything in a patient who is failing.  Just be sure the treatment actually works and is not going to make you worse.

P:  Yes, I remember:  "Above all, do no harm."

P:  Does a very low intraocular pressure cause macular degeneration? 

Dr. Elliot Werner:  Low IOP causes a type of macular damage called hypotony maculopathy, which is different from macular degeneration.

P:  It is a little frustrating to hear how blood flow, circulation, and low blood pressure might be a factor in NTG, but eye doctors never consider the whole body, just the eye.  What's the deal?

Dr. Elliot Werner:  The emphasis is on "might."  There is no good evidence that that is true, and no treatment except lowering IOP has ever been shown to be effective.  

P:  Do cataracts contribute in any way to the NTG syndrome?

Dr. Elliot Werner:  I have not heard of  any evidence of a relationship between cataract and NTG.

P:  Can astigmatism affect pressure measurements?

Dr. Elliot Werner:  The amount of astigmatism has to be very large to affect the IOP measurement.

Moderator:  Dr. Werner before you leave, do you have a minute to tell us a little about your training?

Dr. Elliot Werner:  I graduated from medical school at the University of Pennsylvania in 1971.  I received ophthalmology training at McGill University in Montreal, and served a glaucoma fellowship with Dr. Stephen Drance in Vancouver, British Columbia, Canada.  My offices are in downtown Philadelphia and Bala Cynwyd, a suburb of Philadelphia.  

Moderator:  I hope we haven't scared you off from returning, doctor.  

Dr. Elliot Werner:  See you all next month.

Moderator:  Thanks, doctor.

End of highlights for August 29, 2001.

On September 5, Dr. Wilson discussed "Inflammation and Glaucoma" in the Chat room. Click here for highlights of that meeting.

Click here for the most recent glaucoma chat highlights and links to the chat archives.

Click here for upcoming glaucoma chat events.