Collaborative Normal-Tension Glaucoma Study (CNTGS)
Chat Highlights
October 15, 2008

On Wednesday, October 15, 2008, Dr. Michael Pro, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Collaborative Normal-Tension Glaucoma Study (CNTGS)".

Moderator: Welcome chatters and Dr. Pro. Tonight we are looking at another research project,the Collaborative Normal-Tension Glaucoma Study. Dr. Pro, what is this study?

Dr. Pro: OK, this came about because glaucoma specialists in the 80's were in disagreement as to whether normal tension glaucoma (NTG) existed at all. Some believed that NTG was true glaucoma, while others thought that NTG was an optic neuropathy that looked like glaucoma. In any event clinicians had had less success in controlling progression of glaucoma in patients with NTG.

P: Why is it still an important study ten years later?

Dr. Pro: Well, it laid some important standards. First, it divided patients into two arms. In one arm patients had to have an IOP lowering of at least 30 percent; in the other the patients were followed until there were any signs of damage. This was one of the first studies that had a specified percentage of IOP drop. Also it was important because it helped to define a poorly understood segment of glaucoma - NTG.

P: Have other studies been made since 1998 to contradict the results of the Collaborative Normal-Tension Glaucoma Study?

Dr. Pro: Not really, most studies have shown a positive effect from IOP lowering. What has been more controversial is defining progression. There is always disagreement in what constitutes progression of visual fields, and every study has been criticized in this regard.

P: Which are the different definitions of progression of visual field taken by the glaucoma specialists?

Dr. Pro: Well, there are algorithms that can come as a software package in the Humphery unit, or a specialist can review the fields and skim the various test points to look for worsening. In general a specialist can perform as well as an algorithm, but these software packages can be very helpful to a general ophthalmologist who does not look at fields as often.

P: How has this study changed the way patients are medically treated?

Dr. Pro: As I said above it has supported the idea of IOP lowering in all sorts of situations. Before this study showed a benefit in treating patients who had a pressure lower than 21, some patients were not treated as aggressively as today.

P: Did the results of this study help in the understanding of other forms of glaucoma?

Dr. Pro: This study was pretty small compared to AGIS or OHTS—only 260 subjects from 24 centers—but it did help to understand which NTG patients who would benefit the most from treatment. In this study, that meant patients without a baseline disc hemorrhage, females, patients with a family history of glaucoma, and patients with lesser amounts of disc excavation, among a few other risk factors.

P: The study mentioned, "should fixation be split or threatened, early treatment may be employed, though the CNTGS has shown that these patients are at no greater risk of progression." What does "fixation split or threated" mean?

Dr. Pro: Split fixation refers to when the scotoma, or area of glaucoma damage in the visual field, comes into the area of central vision.

P: Were there factors that were thought to be risks that the study proved were not risk factors?

Dr. Pro: Well, the disease seemed to be less progressive in Asian patients, and this was not expected. Also, Age and IOP levels did not show up as factors for rate of progression in patients with NTG.

P: In the last the years, is there any more understanding as to which patients will progress quickly to profound visual loss?

Dr. Pro: I think this study helped to show that women, migraine sufferers, and patients who present with disc hemorrhages are at greater risk of progression. Since this study, we now think that hypertension and diabetes may be additional risk factors for developing glaucoma or progressing.

P: Was the 30 percent decrease in IOP for those NTG patients with demonstrated progression, arbitrarily used in this study, or were there other studies that showed the percentage should be thirty?

Dr. Pro: I think 30 percent was a commonly used standard of treatment.

P: I have NTG with severe damage to the optic nerve in my left eye and moderate damage in my right eye. I was started on Xalatan for two weeks but only dropped the pressure from 17 to 16. The doctor has now added Timolol. He wants to get the pressure down by 30-40 percent. Is this aggressive enough? Would SLT be beneficial?

Dr. Pro: According to the CNTG study, he is right to try to lower the IOP by 30 or 40 percent. SLT can sometimes work even in patients with NTG.

P: Did the study show rapid progression in people with Raynaud's Syndrome?

Dr. Pro: Other studies have discussed occlusive vascular disease. This study did not find that link (but may have been too small to really look for that connection).

P: Have the patients used in the study been followed to track the progression/non-progression of their disease ten years later?

Dr. Pro: I have not seen any ten year papers from the CNTG study, so I think the patients have been lost to follow-up.

Moderator: Dr. Pro, it's time to say goodnight. Thank you once again for your generous donation of time to the chat room!

Dr. Pro: It's a pleasure. Good night everyone.

On November 5, Dr. Pro discussed "Trabeculectomy, The First Three Months" in the Chat room. Click here for highlights of that meeting.

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