NTG from a Neuro-Ophthalmologist Point of View
Chat Highlights
May 4, 2005

On Wednesday, May 4, 2005, Dr. Mark Moster and the glaucoma chat group discussed "NTG from a Neuro-Ophthalmologist Point of View."

Moderator:  Welcome, Dr. Moster. Thanks for joining us again.  For those who are not familiar with your background, will you please tell us a little about it?

Dr. Mark Moster:  I am a neuro-ophthalmologist, first trained in neurology and then neuro-ophthalmology.

Moderator:  As a neuro-ophthalmologist, what are you looking for when you first examine someone diagnosed with normal-tension glaucoma (NTG)?

Dr. Mark Moster:  I will usually see someone with NTG when an ophthalmologist questions whether there may be a cause for the NTG other than glaucoma.  My goal is to be sure there is not another problem that should be treated in a different manner.

P:  Under what circumstances would a general ophthalmologist, or even a glaucoma specialist, have an NTG patient examined by a neuro-ophthalmologist?  Do you think that occurs as often as it should?

Dr. Mark Moster:  I think it likely does occur as often as it should.  When there is something atypical about the clinical presentation or course, I think that is an appropriate circumstance.

P:  Does every NTG patient you see undergo the same kinds of tests and examinations, or does that depend on individual symptoms?

Dr. Mark Moster:  I think the clinical examination is the same for all patients.  It includes a thorough history and an examination that looks for findings that may not be typical for glaucoma. Depending on the results of the exam, the testing may be different.

P:  Will you please give a couple examples?

Dr. Mark Moster:  Patient A has typical optic disc cupping, but has headaches and mainly temporal-sided visual field defects.  An MRI (magnetic resonance imaging) is performed that shows a pituitary tumor.  Patient B has had a gastrectomy (stomach removal) for ulcers.  There is progressive visual loss.  A blood test for vitamin B12 reveals a very low level.  The patient is treated with vitamin B12 shots.

P:  If I had a bout of optic neuritis that was undiagnosed at the time, would it be possible to tell now?

Dr. Mark Moster:  It is usually possible to tell that the optic nerve has been affected by some illness.  In some, but not all, cases, it is easy to tell that it was optic neuritis.

P:  Could a glaucoma specialist tell, or would I need to see a neuro-ophthalmologist?

Dr. Mark Moster:  A glaucoma specialist is typically good at knowing who should see a neuro-ophthalmologist, since glaucoma specialists are comfortable assessing the optic nerve.

P:  Are there other neurological conditions that could be misdiagnosed as NTG?

Dr. Mark Moster:  The most important neurologic condition that can be missed is a mass lesion pressing on the optic nerve or further back in the visual pathway.  It could be a tumor or an aneurysm.  Other things that can be missed include a prior episode of a loss of blood flow to the optic nerve, prior inflammation, vitamin deficiencies, degenerative diseases, etc.

P:  You mentioned prior inflammation. Would that be the same as being told that "your optic nerve is very enlarged?"

Dr. Mark Moster:  “Enlarged” can mean several things. It may just be large, which isn't bad at all.  It may be elevated or swollen, which is not good, due to inflammation, infection, loss of blood flow, high blood pressure, compression from tumor, or elevated pressure in the brain.

P:  Are there other glaucomas besides NTG that could have neurological causes?

Dr. Mark Moster:  Well, a lot depends on how people define diseases.  For instance, many people feel that NTG and POAG (primary open-angle glaucoma) are really the same. If that is the case, and we believe that NTG is neurological, then POAG by definition also would be neurological, although intraocular pressure may play more of a role in NTG.

P:  Wouldn't something atypical include sudden vision loss? What about damage in only one eye (monocular)?

Dr. Mark Moster:  Yes, sudden visual loss is atypical, except in acute-angle closure glaucoma.  Monocular damage occurs in NTG, but I would be a little more careful in considering neurologic causes if it is monocular.

P:  We have heard that a diminished blood flow and oxygen supply to the optic nerve may be a factor in the development of NTG.  If that is so, wouldn't you have to classify NTG as an ischemic optic neuropathy (ION)?  If NTG is a form of ION, why would treatment focus on lowering intraocular pressure?

Dr. Mark Moster:  The key to what you said is "may be."  Although blood flow may be diminished, it may be secondary to the loss of nerve fibers in the optic nerve and not the cause of the problem.  Also, treatment of blood flow has not been proven to really help.  IOP is lowered because it does help.

P:  Has the treatment of blood flow not been proven to really help because of the difficulty of actually improving microcirculation at the level of the optic nerve head, or because such improvement, even when achieved, does not seem to help?

Dr. Mark Moster:  I think it may be both.

P:  Is there any way to detect a prior episode of loss of blood flow to the optic nerve?

Dr. Mark Moster:  The changes in the optic nerve are typically optic pallor, that is, paleness of the nerve.  There may be cupping of the optic disc as well, particularly if the blood loss was due to an illness know as giant cell (or temporal) arteritis.

P:  Doesn't paleness of the optic nerve head suggest an event, such as loss of blood flow to the optic nerve, rather than glaucoma?  Also, how long after an ischemic event does this paleness continue?

Dr. Mark Moster:  In glaucoma, the enlarged cup may be pale, but not the rim of the optic nerve.  In virtually all neurologic causes of optic nerve disease, the rim will be pale. That includes loss of blood flow.

P:  Is that permanent?

Dr. Mark Moster:  Yes, it's permanent.

P:  Can't you also have optic pallor from any early loss of vision, such as from congenital cataracts and/or amblyopia?

Dr. Mark Moster:  All neurologic causes of optic nerve disease cause pallor.  However, the optic nerve in the average amblyopia patient usually appears to be normal.

P:  What are some other neurological causes of glaucoma?

Dr. Mark Moster:  Other neurologic causes include diseases that cause pressure to move forward, such as thyroid ophthalmolopathy or a carotid-cavernous fistula.  [Note: Carotid-cavernous fistulas (CCFs) are abnormal communications between the carotid arterial system and the venous cavernous sinus.]

P:  If the optic nerve fiber measures in the "bottom 1%," what does that mean?

Dr. Mark Moster:  For me it would really depend upon what test was performed and how valid it was.  However, 1% certainly seems quite low and would mean that a lot of nerve fiber loss has occurred.

P:  Are there reliable ways to measure blood flow to the optic nerve?

Dr. Mark Moster:  In the real clinical world, there are no excellent ways of measuring blood flow to the optic nerve.  Fluorescein angiography or color Doppler techniques provide some information, but they are of little help to most clinicians treating glaucoma.

P:  Do you think that taking aspirin every day helps increase blood flow to the optic nerve?  Is there any proof that it does help?

Dr. Mark Moster:  I certainly recommend it to anyone who has risk factors for vascular disease (hypertension, cholesterol, smoking, family history).  However, we don't have proof that it works. In fact, in the Ischemic Optic Neuropathy Decompression Trial (IONDT), a large study on surgery for ischemic optic neuropathy, aspirin did not prevent episodes in the other eye.

P:  From one exam to the next, one of my nerve heads became tilted.  (During this same interval, I had some sort of eye incident which left me with blurry vision that has only partially resolved several years later.)  What could cause this tilt? What effect is it likely to have on my vision?

Dr. Mark Moster:  Tilted optic nerves usually have been that way since birth.  I am not aware of an eye incident that would cause this to occur.  More often, a tilt might be noticed because of a more careful exam after the blurred vision occurred.

P:  I am asking you lots of questions tonight because I had rapid monocular field loss following maxillofacial surgery.  Initially, I was diagnosed with NTG, but I was sent to a neuro-ophthalmologist, had a CT scan, MRI, and various other tests to check and counter-check things.

Over nearly three years, eye drops did not lower my high-normal pressures, but there was no progression.  Damage is in the eye with the lower pressure (lower by one point).  It is now thought I had an ischemic event, or that some odd thing happened during surgery.  I am currently being monitored.

Blood tests revealed very high cholesterol and high hemoglobin count.  After surgery, my normal blood pressure was elevated by more than 30%.  Could anesthesia or any of the blood conditions have caused the optic nerve damage?  Or could bone graft material have entered the bloodstream and caused an occlusion?

Dr. Mark Moster:  I appreciate your questions.  It is very difficult to assess what may have occurred without more information or examining you.  It is true that you can have visual loss related to blood flow during or after surgery.

P:  Should someone with NTG or POAG sleep on a thick pillow to prevent IOP from becoming too low at night?

Dr. Mark Moster:  Let me clarify something:  As a neuro-ophthalmologist, I might diagnose NTG or look for diseases that mimic NTG, but I don't actually treat it.  However, a thick pillow for everybody sounds good to me.

Monitor: I think the good doctor needs to find that pillow soon.  Great having you here again, Dr. Moster. Thank you.

Dr. Mark Moster:  Thank you, and thank you all for your excellent questions.  Good night.

On May 12, Dr. Richard Lee discussed "Neuroprotection" in the Chat room. Click here for highlights of that meeting.

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