NTG Treatments
Chat Highlights
January 6, 2010

On Wednesday, January 6, 2010, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "NTG Treatments".

Moderator: Welcome back Dr Pro. Our topic this evening is NTG Treatments. Let’s begin. What is normal tension glaucoma?

Dr. Pro: Normal Tension Glaucoma means the development of glaucoma with the presence of "normal” intraocular pressure generally thought of as IOP less than 22. That means there is characteristic damage or change to the optic nerve with a visual field deficit that correlates to the area of optic nerve injury.

P: What differentiates a patient with a diagnosis of normal tension glaucoma from a patient with a primary open angle glaucoma diagnosis?

Dr. Pro: In both conditions the angle is open, in contrast to angle closure glaucoma, but the defining difference is the lack of an IOP greater than 21 in NTG.

P: Can a patient have normal tension and another form of glaucoma?

Dr. Pro: Let me begin by saying the NTG is more of a catch-all term and like primary open angle glaucoma (POAG) there are probably different processes at work in different individuals which causes their nerves to be damaged. We are just beginning to understand the various genes and environmental factors at play to cause an individual to develop glaucoma. The latest genetic thinking is that certain genes may cause some individuals to be at greater risk for glaucoma, but there are numerous other factors at play. Anyway that is a long answer to say that NTG may be thought of as a diagnosis of exclusion. You look for other things, such as pseudoexfoliation syndrome. You may check IOP at other times of the day to see if the IOP fluctuates widely and is sometimes over 21. In some cases where the nerve or visual field seem abnormal you may even order brain imaging to make sure that nothing else is going on, but in the end you may label the condition as NTG if nothing else turns up.

P: If damage is happening at normal pressures, does that mean that lowering the IOP doesn't work to control NTG?

Dr. Pro: No, in fact the Collaborative Normal Tension Glaucoma Study showed that a 30% IOP reduction slowed the rate of visual field loss in NTG patients. In fact the treatment generally is similar to POAG, with drops and/or laser trabeculoplasty generally started before surgery. It may not seem to be as much because the starting IOP was not too high to begin with, but the IOP reduction on average is probably similar, about 20%.

P: If drops can get the IOP low enough, what's the best option in cases of NTG?

Dr. Pro: That may differ from surgeon to surgeon, but I feel that Trabeculectomy is effective in achieving a post-op IOP as low as is often necessary in these patients.

P: Is a trab usually successful in lowering pressure enough to stop damage?

Dr. Pro: Trabs are effective in lowering the pressure to a desired range in about 80% of cases. We can never promise to stop all glaucoma damage, but often by lowering the IOP the rate of glaucoma worsening can be slowed tremendously.

P: My blood pressure dips low overnight (discovered by wearing a BP monitor for 48 hrs) so I now take salt (actually V-8 juice) before going to sleep. Can this eliminate the need for drops?

Dr. Pro: Great point and the answer is, “I don't know." It depends on what your untreated IOP is. But you raise an interesting issue. There is a school of thought that considers NTG to be a disease of defective blood flow to the optic nerve and retina. If the BP gets too low overnight, then the blood flow to the optic nerve may be insufficient.

P: Yes, that's the theory and the hope that raising BP at night will nourish the optic nerve sufficiently. Hard to know if it's doing that, though. Thanks for the response.

Dr. Pro: Well, sometimes we just need to follow along with visual fields and nerve imaging in people with low overnight BP, who are trying to increase the BP with salt.

P: What happens next if the Trab cannot keep the pressure down?

Dr. Pro: Well we always have other treatment options, like going back on glaucoma drops, having a laser, or having another surgery: a repeat trab or tube shunt, depending on the examination and surgeon preference.

P: What are some other causes for NTG?

Dr. Pro: As I mentioned, with both NTG and POAG, we don't really know why an individual is affected and another person with the exact same IOP range is unaffected, but treatment is very similar. Just like POAG, we find that the two most effective primary drops are prostaglandin analogues (Xalatan, Lumigan, etc.) or Timolol (a beta blocker).

P: Do all patients with NTG diagnosis get referred to see a neurologist or a neuro-ophthalmologist?

Dr. Pro: No, most do not.

P: When would one?

Dr. Pro: In cases where the nerve does not go along with the amount of visual field loss (the nerve looks good, but the field does not). I tend to see more central visual field damage in NTG.

P: I want to thank whoever came up with this idea to have this website and chat. It is the best invention since ice cream. Thank all the doctors and the moderators. Goodnight.

Moderator: Thanks; it was a group effort and continues to be a group effort! I hope to see all the new chatters back in two weeks for another chat with Dr Pro in which we will chat about glaucoma medications. Come with your questions ready!

Moderator: Thank you Dr Pro!

Dr. Pro: You're welcome. See you in two weeks.

On January 20, Dr. Pro discussed "Glaucoma Medications" in the Chat room. Click here for highlights of that meeting.

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