Normal-tension Glaucoma
Chat Highlights
March 12, 2003

Norma Devine, Editor

On Wednesday, March 12, 2003, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Normal-tension Glaucoma."

Dr. Rick Wilson:  Hello, everyone.  Any questions about normal-tension glaucoma (NTG)?

P:  I had been treated for NTG with drops for three years.  Then a new doctor took over my case.  Even though I have changes in my optic nerve, the new doctor took me off the drops, because my intraocular pressures are not high.  I am confused.  My mother has severe glaucoma and has many problems.  Should I be using drops to treat my NTG? 

Dr. Rick Wilson:  If you have damage and your mother has severe damage, the chances are you should be on drops.  I can't say for sure without an examination.

P:  What kind of factors are involved in diagnosing NTG?   The word "normal" makes it sound as if all is okay. 

Dr. Rick Wilson:  The word "normal" only refers to the IOP the patient has.

P:  My pressure readings are only 19 and 20 mm Hg, yet I have 90% degeneration of the cup in one eye.  Is that NTG?  I am new to this, and have been to the doctor only once, so far.

Dr. Rick Wilson:  A common misdiagnosis occurs when a patient has normal IOPs at the doctor's office, but much higher IOPs in the early morning or when reclining at night.  The IOP of 19 and 20 mm Hg is so close to abnormal that you would probably not fall into the classical NTG diagnosis.

P:  Dr. Rick, what do you think he means by "90% degeneration of the cup in one eye?" 

Dr. Rick Wilson:  I think he means he has a 90% cup.  If he started with a small cup, say 0.2 to 0.3,  then he has lost about 90% of his nerve fibers. If he started with a .6 cup or 60% cup, that means he has lost much less.

P:  It has been stated before that NTG is a "wastebasket" diagnosis.  If the element of thin corneas is added to the risk factors, is that still considered NTG, or are some NTG patients really not so "normal" in IOP measurement?

Dr. Rick Wilson:  NTG is a wastebasket diagnosis, with many etiologies playing a role.  Some people with "normal" pressures have thin corneas that test artificially low and really have elevated IOP and primary open-angle glaucoma.  About 1/6 of primary open-angle glaucomas are NTG, and the prevalence goes up markedly in the elderly.

P:  How is the diagnosis of NTG made?

Dr. Rick Wilson:  NTG looks just like primary open-angle glaucoma (POAG), so the diagnosis is based on the normal parameters of nerve damage and visual field loss.  It's just that there is no elevated IOP.

P:  I was diagnosed with NTG in November and placed on Travatan.  After one month, my pressures

went from 20 to 14 mm Hg. Then, in January, I was placed on Xalatan and my pressures went up to 18 mm Hg and then down to 16 mm Hg this month.  Is that normal after switching drops?

Dr. Rick Wilson:  One problem, if your doctor doesn't change the treatment of one eye at a time, is that it is impossible to sort out whether the change is due to the time of day or the drug. 

P:  Is the structure of the optic nerve different in patients with NTG than in patients with primary open-angle glaucoma?  

Dr. Rick Wilson:  Sorry, we don't know that.  That is one theory.  Other theories are:  vascular supply, systemic hypotension (low blood pressure), nocturnal hypotension,  and nocturnal systemic hypotension (Sohan Hayreh). 

P:  What's the relationship between systemic blood pressure and intraocular pressure?

Dr. Rick Wilson:  There is a diurnal curve of blood pressure similar to the diurnal curve of intraocular pressure. As with eye pressure, the blood pressure is at its lowest during the early morning hours. In patients with hypertension (high blood pressure), the lowest pressures are between 2:00 a.m. and 4:00 a.m.  Two-thirds of the normal population will have a blood pressure drop of greater than 10% during this period. These people are termed "dippers." Stephen Drance has found a much higher incidence of progression in POAG among dippers than among non-dippers.   

Dr. Rick Wilson:  Patients with systemic hypertension usually evidence a much greater swing in systolic and diastolic blood pressure, with an average of a 26% drop from day to night.  Hypertensives treated with beta blockers can have diastolic blood pressures during sleep of 50 mm Hg or less, and rarely down to 30 mm Hg or less.  An abnormally deep dip may compromise local vascular supply.  

P:  Do NTG patients have more migraine headaches than POAG patients?

Dr. Rick Wilson:  The incidence of migraines is much higher in NTG patients than in the general population, which suggests a vasospastic component to NTG.

P:  Do glaucoma eye drops work better for POAG than for NTG?  My question really refers to how much medication is required to reduce the IOP of a NTG patient to the target IOP.  The reduction in IOP is less than in POAG, but the percentage of the decrease is more significant.

Dr. Rick Wilson:  You're right.  It is the percentage drop that is the real point.  A patient with a pressure of 40 mm Hg may come down to 25 mm Hg on one drug, but someone with a pressure of 12 mm Hg might only come down to 9 mm Hg.  It is harder to go below 9 to 10 mm Hg, because that is the pressure of the blood in the vessels that the eye is trying to drain to.

P:  At what intraocular pressure do you like to keep NTG patients? 

Dr. Rick Wilson:  That depends upon the extent of the damage to the optic nerve and the loss of visual field.  If the damage is minimal, I will reduce the IOP about 30% and watch them carefully.  If the damage is serious, I would like the IOP in the 12 mm Hg or under range.

P:  I had my IOPs measured every four hours for a 20-hour period to make sure my pressure did not spike at certain times.  It didn't.  Does that confirm the diagnosis of NTG?  

Dr. Rick Wilson:  If you were not on medications at the time and your IOP stayed in the 22 mm Hg and under range.

P:  I read that high pulsatility indexes and low systemic blood pressure at the end diastolic phase has been found in NTG patients.  What are the implications of that and the treatment for it?  

Dr. Rick Wilson:  Low blood pressure means that there is less pressure pushing the blood into the eye against the pressure in the eye. That is a serious risk factor for damage.  Medications that increase blood pressure can help. 

P:  Although I have lost 90% of the optic nerve, I see remarkably well with the remaining 10%.  I have been under a doctor's care for nearly 15 years.  What is the prognosis?  

Dr. Rick Wilson:  That depends on whether your visual field is stable or  whether you have had progression over the last few years.

P:  Is the pattern of vision loss for persons with NTG different from that of other glaucoma patients?

Dr. Rick Wilson:  Often the visual field loss is dense and close to the center of the vision, rather than being 10 to 20 degrees off the center of vision.

P:  Is NTG linked in any way to poor circulation?

Dr. Rick Wilson:  Yes, as I noted earlier, low blood pressure, vasospasm, or abnormal clinching of the blood vessels (which shuts down blood flow), and the inability of the vessels to dilate or contract normally in response to more demand from the eye, or higher blood pressures, all may have a role in NTG.

P:  Therefore, the optic nerve of those so affected is more susceptible to damage?

Dr. Rick Wilson:  It seems more susceptible to the damaging effects of IOP.  Autoimmune disease may also play a role.

P:  So, again, this is a hemodynamic problem?

Dr. Rick Wilson:  That is what we suspect in many people.

P:  Do many glaucoma specialists think there is no such disease as  normal-tension glaucoma?

Dr. Rick Wilson:  We may argue about the semantics, but we can agree that some individuals get damage that looks exactly like glaucoma damage at normal IOPs.

P:  I have NTG and considerable loss of vision in the left eye.  I had a trabeculectomy on the left eye last fall, and the doctor is pleased with the results.  There are no signs yet of loss of vision in that eye.  Is it inevitable that the right eye will also eventually lose vision, or do some NTG patients not suffer loss of vision in both eyes?  

Dr. Rick Wilson:  My father had very asymmetric NTG,  and both eyes were stabilized for 16 years on medication.  So, no, the other eye does not necessarily have to progress.

P:  Can ocular blood pressure be measured (color Doppler method)?  If an abnormality is found, what is the treatment?  What is the role of betaxolol (a beta blocker)?   

Dr. Rick Wilson:  The color Doppler can measure the blood flow to the back of the eye grossly.  It cannot distinguish the individual, short, posterior ciliary arteries that seem to be the supply to the optic nerve.  The best known treatment for poor circulation is aspirin, exercise, weight loss, and a healthful diet.  Betaxolol may exert a calcium-channel blocking effect to help vessels stay more dilated.  That is not a proven benefit; however, betaxolol seems to protect the visual field as well as timolol, which lowers eye pressure more, so there may be a real effect from betaxolol. 

P:  Are calcium channel blockers used very much to treat NTG?

Dr. Rick Wilson:  Not any more.  They had serious side effects, and it was not clear how much good they were doing.  In fact, in patients where low blood pressure could be part of the equation, calcium channel blockers could make the situation worse by lowering blood pressure too much.

P:  I have NTG, with IOPs of 22 and 21 mm Hg, and vision loss in the right eye.  During the initial exam, the ophthalmologist said the rim of my optic nerve was "pale."  It's my understanding that a pale nerve is indicative of vascular spasm. Is that correct?

Dr. Rick Wilson:  Or poor circulation, or a past mini-stroke, or compression on the nerve, etc.

P:  I am concerned about your answer about low blood pressure.  We are supposed to be exercising to lower our blood pressure, but if I think I am borderline low blood pressure, or low normal, and have thin corneas, how would raising my blood pressure with drugs help?

Dr. Rick Wilson:  Exercise usually raises blood pressure that is too low.  If your blood pressure is too low (for example, 80 /45 mm Hg), then raising your blood pressure will help blood get into the eye to the nerve.

P:  I suffer from Raynaud's syndrome.  Is that linked to NTG?   Please explain the risk factor of  autoimmune conditions. I have a bunch of them!

Dr. Rick Wilson:  Raynaud's is a vasospastic condition of the extremities.  My wife has it.  There is a higher prevalence of Raynaud's in patients with NTG, as well as a higher prevalence of glaucoma in those with autoimmune diseases.

P:  The connection with Raynaud's makes sense -- vasospasm in the extremities may translate to vasospasm in vessels that supply the optic nerve. What is the connection with autoimmune diseases?

Dr. Rick Wilson:  We don't know yet.  Sorry.  

P:  So why aren't most of us without known risk factors being checked out for pressure spikes, uneven circulation, and low blood pressure as a regular part of our treatment? 

Dr. Rick Wilson:  Unless you have the diagnosis of NTG, we rarely go to that extent.  If you do have NTG, then we go the extra mile, but most general ophthalmologists don't have the specialty training to that extent.

P:  How does hemoconcentration, a Hct of 52%, affect blood flow in the eyes of a person with NTG?

Dr. Rick Wilson:  Polycythemia vera is a disease in which the percentage of blood cells to blood volume is too high.  The blood gets sluggish as it goes through the vessels, especially the small vessels, and is a risk factor for glaucoma.

P:  I suspect I have poor circulation because I often get dizzy spells when my exercise routine is disrupted.  I do not usually get headaches, but feel heavy in the head.  I also have tinnitus.  Some of my blood pressure measurements have been very low.  I have cold hands and feet.  I am addicted to exercise (aerobic) because everything goes so well when I stay on routine.  I have a healthy diet.  What should be my next step?

Dr. Rick Wilson:  I would take your medication religiously and have your optic nerve and visual field followed closely. Sounds like you're doing most everything right.

P:  Is it true that Alphagan should not be used to treat NTG because, as an adrenergic agonist, it can cause vascular spasms?

Dr. Rick Wilson:  We don't know for sure, but we think not.  Many eye MDs use Alphagan to treat NTG because they think it may be neuroprotective.

Dr. Rick Wilson:  I'm sorry to have to run, but I leave for Athens to give some lectures tomorrow, so have to pack.   Everyone have a good week.  I can pick up the rest of the questions next week.

End of highlights for March 12, 2003.

On March 19, Dr. Wilson discussed "New Glaucoma Surgeries" 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.