Primary Open-angle Glaucoma
Chat Highlights
April 16, 2003

Norma Devine, Editor

On Wednesday, April 16, 2003, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Primary Open-angle Glaucoma."

Moderator:  The topic tonight is primary open-angle glaucoma (POAG).

Dr. Rick Wilson:  Primary open-angle glaucoma is the garden-variety open- angle glaucoma.  "Primary" means there is no known cause.

P:  Is POAG the most common of all glaucomas?

Dr. Rick Wilson:  It is in America.  In China, primary angle-closure glaucoma is the most common type.

P:  Does "open-angle" mean the angle is normal?  

Dr. Rick Wilson:  It just means that the iris is not in apposition or blocking the trabecular meshwork. That is, the iris is not up against the trabecular meshwork, the eye's "drain."  

P:  Are there other types of POAG?

Dr. Rick Wilson:  Not really. There are many types of secondary, as compared to open- angle, glaucoma. However, they are not primary.

P:  Which differences can be seen with microscopy?

Dr. Rick Wilson:  With primary, open-angle glaucoma, the changes seen are the result of aging, with loss of cells lining the beams of the meshwork, and a build-up of debris and thickening of the beams.

P:  Is open-angle glaucoma the most treatable form?  

Dr. Rick Wilson:  No.  If caught early, angle-closure glaucoma often may be reversed.

P:  What percentage of  glaucoma patients in the United States have POAG?

Dr. Rick Wilson:  My recollection is about 80% to 85%.  About 5% to 10% have angle-closure glaucoma, and the rest have a secondary glaucoma.

P:  Does POAG generally go undetected more than other types of glaucoma?

Dr. Rick Wilson:  Yes, because it has the fewest symptoms.

P:  Is POAG the main type of glaucoma that leads to blindness?

Dr. Rick Wilson:  Actually, no.  Primary angle-closure glaucoma may be less prevalent on a worldwide basis.  But it leads to blindness much more frequently than open-angle glaucoma, so probably causes more blindness than open-angle glaucoma.

P:  In your opinion, is POAG very treatable because the frequency of occurrence has encouraged more research? 

Dr. Rick Wilson:  No, it is because POAG is less virulent than some of the other types.

P:  In the treatment of POAG, at what point is surgery inevitable?  Can drops be sufficient?  I was under the impression that surgery was a substitute for the continuous use of drops.

Dr. Rick Wilson:  Usually in America we use drops until they no longer control the IOP (intraocular pressure).  If laser and drops cannot control the IOP, then surgery would be the next step.  In Great Britain, they turn to surgery much earlier.

P:  My understanding was that POAG is more prevalent in dark-eyed people.  My daughter, who is fair-skinned and blue eyed, was just told by her eye-care doctor that it is more common with fair-skinned, light-eyed people.  Is that true?  

Dr. Rick Wilson:  I've never heard of an iris-color correlation with POAG.

P:  Which medication is considered the front line of defense against POAG?

Dr. Rick Wilson:  Usually one of the prostaglandins or a beta blocker.

P:  Can you give an example of a prostaglandin?

Dr. Rick Wilson:  Xalatan, Travatan, Lumigan, and Rescula are prostaglandins.

P:  What percentage of POAG patients use pilocarpine?  Why isn't that more widely used?

Dr. Rick Wilson:  Pilocarpine has to be used four times a day for optimum control of IOP.  Most patients find that hard to do.  It also makes the pupils small, so everything looks dim, and adapting to darkness is difficult or impossible.

P:  Does treating POAG differ from treating other forms of glaucoma, and if so, how?

Dr. Rick Wilson:  POAG, along with pseudoexfoliative, pigmentary, and low-tension glaucoma, is more treatable with laser trabeculoplasty.

P:  So, the angle is normal?

Dr. Rick Wilson:  To inspection at the slit lamp.  Electron microscopy can reveal differences from a normal angle. 

P:  Is it true that longer a patient uses glaucoma medication, the less successful surgery will be?  I mean long-term use of the medications.  

Dr. Rick Wilson:  Yes, that is true, although the intraoperative use of mitomycin has lessened the effects of long-term medications on the success of the trabeculectomy.

Moderator:  Is normal-tension glaucoma also primary open-angle glaucoma?

Dr. Rick Wilson:  It is one type of POAG and makes up about 1/6 of POAG patients.

P:  Do different types of glaucoma have different patterns of visual field loss?

Dr. Rick Wilson:  Normal-tension glaucoma is the main type of glaucoma that stands out,  and it often is subtle.

P:  When you say that NTG is the "main type of glaucoma that stands out," are you referring to the pattern of the visual field defects?

Dr. Rick Wilson:  It's the main type of glaucoma that seems to affect the visual field in a special way.

P:  What clinical differences, besides IOP, do you actually see between NTG and POAG? 

Dr. Rick Wilson:  Normal-tension glaucoma often has deeper visual field defects closer to the center of vision.

P:  I'm sorry my understanding isn't better, but what do you mean by "deeper visual field defects?"

Dr. Rick Wilson:  Denser defects, in which the patient cannot see a brighter light that he or she would easily see if the defect were more shallow. 

P:  Is the cause of this different visual field pattern in NTG known?

Dr. Rick Wilson:  No, although circulation is suspected.

P:  My IOP shot up over a month to 40 mm Hg.  Is that characteristic of open-angle glaucoma?  

Dr. Rick Wilson:  If medications are not being used, open-angle glaucoma is characterized by swings in IOP over the course of a day that measure on average 11 mm Hg.  Sudden rises in IOP, when everything else is the same, are unusual.

P:  I seem to recall reading that the slope and/or shape of the cup in normal-tension glaucoma is a little different from that of POAG, indicating a different mechanism is at work.  Can you comment, please?

Dr. Rick Wilson:  For the same amount of visual field damage in normal-tension glaucoma, the cup is slightly bigger than it is in POAG.  We think that the causation of normal-tension glaucoma may be more related to blood circulation than it is in POAG.

End of highlights for April 16, 2003.

On April 23, Dr. Wilson discussed "Neovascular Glaucoma" in the Chat room. Click here for highlights of that meeting.

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