The Normal-Tension Glaucoma Workup
Chat Highlights
February 22, 2006

On Wednesday, February 22, 2006, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "The Normal-Tension Glaucoma Workup."

Moderator:  Tonight's topic is “The Normal-Tension Glaucoma Workup.”  Dr. Wilson, what constitutes a workup, and what is normal-tension glaucoma (NTG)?  

Dr. Rick Wilson:  A workup is the diagnostic examination of the patient, both physical and with diagnostic machines in the laboratory.  Normal-tension glaucoma is a wastebasket term for  multiple entities that produce optic nerve damage, which appears to be glaucoma, but without an elevated intraocular pressure (IOP).

P:  What are some of the things you look for in the diagnosis of NTG?

Dr. Rick Wilson:  The first thing to do is to make sure the patient really has glaucoma.  The optic nerve could naturally have a large physiologic cup; that is, looking like glaucoma but not being glaucoma.  An old retinal branch vein occlusion, retinal hemorrhage, retinal detachment, tumor, or ischemic optic neuropathy could produce a visual field that looks like glaucoma, but is caused by something else.  Multiple sclerosis, optic nerve drusen, or a tumor compressing the optic nerve also could resemble glaucoma enough to fool all but a careful observer.

P:  After determining that the patient has glaucoma, what comes next?

Dr. Rick Wilson:  The next thing to rule out is that the patient just has the garden-variety, primary open-angle glaucoma.  For example, the patient may have thin corneas, say after refractive surgery or just naturally, which give a falsely low IOP.  The patient may have large swings in IOP during the day that have been missed.  Perhaps the patient is now on a systemic beta blocker that is lowering the IOP,  but was not using a beta blocker when the damage to the optic nerve occurred.  Or the patient could have had a traumatic, steroid-induced, or inflammatory glaucoma in the past that did the damage, but the condition has improved and the IOP is normal.

P:  What are some of the causes of NTG that could be treated?

Dr. Rick Wilson:  Treatable causes are an irregular heart rhythm or a blood problem, such as severe anemia, or blood too thick, as in polycythemia vera, or one of the hyper viscosity syndromes, or platelets that are too sticky.

P:  What are polycythemia vera and hyper viscosity syndromes? 

Dr. Rick Wilson:  A person with polycythemia vera has far too many red blood cells, so the blood is so thick it has a hard time getting through the small blood vessels, like the short posterior ciliary arteries that supply the optic nerve.  If there is too much serum protein in the blood, it can make it so thick the same problem occurs, that is, high viscosity.

P: What are some of the causes that may not be as treatable as those you mentioned?

Dr. Rick Wilson:  They may be systemic blood pressure that is too low, possibly only at night, or a vasospastic syndrome, such as migraine or Raynaud's syndrome.   Sleep apnea is thought to be a contributing factor, and autoimmune disease rounds out the other possible causes that might be treated. 

Moderator:  The diagnosis of NTG seems complicated and time consuming.  

Dr. Rick Wilson: The physician can make a tentative diagnosis, but is then obligated to try to find a cause in the hope that it might be something treatable.  I always involve a good internist to help me look for systemic causes.

P:  Would an ophthalmologist be able to recognize glaucoma and treat it, or is a glaucoma specialist required?  

Dr. Rick Wilson:  A good general ophthalmologist should be able to recognize and treat straight-forward glaucoma.  A specialist is helpful if the diagnosis is in doubt or the therapy does not seem to be stopping the damage.

P:  We seem to have quite a few younger patients diagnosed with NTG and being treated for it.  How common is NTG in 40- and 50-year old people?   

Dr. Rick Wilson:  I rarely see NTG in the under 60 set, and then it is usually in women with unusually low systemic blood pressure.

P:  What do you consider to be low systemic blood pressure?

Dr. Rick Wilson:  Lower than 90/60 mm Hg is my general guideline.  That pressure, however, may only be seen at night or intermittently.  At night when a person lies down, the IOP rises a couple of mm in normals, but may rise abnormally in some patients with glaucoma.  Having a low blood pressure when the eye pressure is the highest reduces the force of blood being pushed into the eye against the pressure in the eye.  That cuts down blood flow to the optic nerve.

P:  Does a low blood pressure of 90/60 mm Hg also have an adverse effect on the optic nerve during the day when the patient is upright and awake?   

Dr. Rick Wilson:  At any time, if the blood pressure drops too much below 90/60 mm Hg, the force of the blood being pushed into the eye may not be adequate.

P:  Is there a certain IOP range that is seen most often in NTG?

Dr. Rick Wilson:  Having all recorded pressures less than 22 mm Hg would qualify as NTG.

P:  I was diagnosed with NTG at age 44 and had my first trabeculectomy less  than four years later. There are so many other possibilities that you've mentioned, and I highly doubt that they were all ruled out.  I do, in fact, have (untreated) sleep apnea and high cholesterol and my mother has both polycythemia vera and atrial fibrillation, among other physical problems.  I am soon to be scheduled for a trabeculectomy in my other eye.  Should I be requesting further work-ups before I proceed with another trabeculectomy? 

Dr. Rick Wilson:  I certainly would want a thorough physical examination looking for any cause for decreased blood flow or neurologic problem.  A 24-hour blood pressure measurement would also be an easy thing to do.  I would certainly treat the sleep apnea if it is significant.

P:  Thank you.  The sleep apnea was determined to be only mild when diagnosed a few years ago.  I haven't had it rechecked since then.  Should I?   I also had an MRI to rule out a tumor pressing on the optic nerve.  Are my mother's polycythemia vera and atrial fibrillation of concern to me and my NTG diagnosis?

Dr. Rick Wilson:  A CBC and EKG (blood count and heart tracing) would easily answer that.  Since sleep apnea seems to raise IOP when the patient is sleeping, you may want to have that rechecked. Remember to get a good internist's evaluation, if you haven't had one.  

P:  I have NTG.  The IOP in one eye is consistently a point lower than the IOP in the other eye.  I have optic nerve damage in the eye with the lower pressure, and no apparent progression over several years.  My subjective experience of vision loss is that it was sudden. 

The workup I have had, aside from the usual office exams, includes an EKG, pachymetry (corneal curvature measurement), CBC (blood work), CT scan (specifically to check sinuses), and an MRI (to look for head tumors).  I have regular exams now every three to four months, as well as periodic visual field tests, HRT's, and photos of the optic nerves.  I am no longer on medication.

 The damage to my optic nerve occurred during or shortly after dental surgery under general anesthesia.  After surgery, the eye was quite bloodshot. The only other red flags are high cholesterol and somewhat thick blood, found through the CBC. The damaged eye, brow, and temple area have been generally uncomfortable.  

Dr. Rick Wilson:  According to one expert, 50% of the patients that look like normal-tension glaucoma never progress. Especially if your damage was rapid without a high pressure, it is unlikely to be glaucoma.  Perhaps your blood pressure was low during the dental surgery and your eye was not getting as much blood as it required.   The workup seems adequate and the proof of the pudding is there has not been any change in several years off of medicine, if I understand you correctly.

P:  What role, if any, might sinus problems play in glaucoma?  

Dr. Rick Wilson:  Sinus infections, especially if chronic, might cause intraocular inflammation that could cause glaucoma or, if very chronic, erode the bone and cause pressure on the optic nerve.

Moderator:  Dr. Wilson, it's the bottom of the hour. Thanks so much for sharing your time and knowledge. 

Dr. Rick Wilson:  My pleasure, SteveBC. You did a great job as moderator.  Have a good week everyone.

On March 1, Dr. Werner discussed "Combination Therapy" in the Chat room. Click here for highlights of that meeting.

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