Primary Open-angle Glaucoma (POAG)
Chat Highlights
July 14, 2004

Norma Devine, Editor

On Wednesday, July 14, 2004, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Primary Open-angle Glaucoma (POAG)."

Moderator:  Dr. Wilson, tonight the topic is primary open-angle glaucoma (POAG).  Is that the most common type of glaucoma?

Dr. Rick Wilson:  Yes, it's the garden-variety glaucoma that most people have.  There is no visible cause for the glaucoma. The angle is open, and even with microscopy it is difficult to tell that there is something amiss with the trabecular meshwork. 

P:  Why doesn't the trabecular meshwork function properly?  

Dr. Rick Wilson:  We don't understand why the trabecular meshwork, the so-called "drain," does not work.  There seems to be a build-up of glycosaminoglycans (GAGs) in the trabecular meshwork. [Editor's note:  GAGs are polysaccharides.]  The cells lining the trabecular meshwork drop out with age and become fewer and fewer.  Since the work of these cells is to clean up debris in the eye, when there are fewer cells to do the work, more debris can accumulate in the trabecular meshwork.  

P:  What are glycosaminoglycans? 

Dr. Rick Wilson:  They look like amyloid under the microscope. We don't know if people with glaucoma make more GAGs than they should or whether their trabecular meshwork does not clean up the normal amount of GAGS.  Either way, the trabecular meshwork contains too many. 

P:  Is amyloid like plaque? 

Dr. Rick Wilson:  There are several kinds of plaque, such as cholesterol in the carotid artery, and plaque on teeth, so I would need to know more about what you mean.  We would need a pathologist to answer some of these questions more accurately.

P:  Is the amyloid plaque found in the brains of Alzheimer's patients the reason memantine is being studied for glaucoma?

Dr. Rick Wilson:  It is thought that memantine might make the retinal ganglion cells more resistant to elevated intraocular pressure.

P:  Is there any evidence that glaucoma is related to (hereditary) amyloidosis?

Dr. Rick Wilson:  There is that connection in patients with pseudo-exfoliation glaucoma. 

P:  Can glucosamine taken as a dietary supplement be converted to glycosaminoglycans, or are they fundamentally different substances that only sound somewhat similar?

Dr. Rick Wilson:  I am not a chemist, but I think the glycan makes the compound much different.  

P:  Do those GAGS look similar to exfoliative material?

Dr. Rick Wilson:  No, the exfoliative material is white and formed into flakes in most areas of the eye.

P:  What is "exfoliative material" and can it be seen with the naked eye?  

Dr. Rick Wilson:  Exfoliative material is a white, flaky material that forms on the surface of the lens in the eye, on the ciliary body in the eye, under the conjunctiva, and in the vessels on the surface of the eye.  The exfoliative material flakes off the lens, floats in the fluid of the eye and gets caught in the drain in the eye, blocking it, and causing exfoliative glaucoma.  You would need magnification and good light to see it.

P:  Isn't exfoliative material also found in the trabecular meshwork? 

Dr. Rick Wilson:  I don't think it is found there naturally, but is sieved out of the aqueous by the trabecular meshwork.

P:  The meshwork has the same cells as the membrane of the kidney.  Is there any increase in kidney problems with glaucoma?  

Dr. Rick Wilson:  There does not seem to be a connection.

P:  Does the presence of exfoliative material cause a decrease in vision?  

Dr. Rick Wilson:  It does not seem to, unless it causes the lens in the eye to dislocate.

P:  Can the flakes caused by blepharitis also clog the trabecular meshwork?

Dr. Rick Wilson:  No, blepharitis is only on the lids in the region of the Meibomian or oil glands.

P:  Does a floater or posterior vitreous detachment impede the flow of fluid through the meshwork? 

Dr. Rick Wilson:  No.  Both of those entities are in the vitreous humor of the eye and cannot make it into the anterior chamber easily.

Moderator:  Is the intraocular pressure (IOP) high in POAG? 

Dr. Rick Wilson:  For most Caucasians, the presenting pressure is in the 20's or 30's.  For African-Americans and Africans, it can be in the 40's and 50's.  

P:  Are African-Americans and Africans more at risk for glaucoma than other races?  

Dr. Rick Wilson:  African-Americans are four times as likely to have glaucoma, and six times as likely to be blind from it.  Unfortunately, they are only half as likely to be treated for it.  On average, they get glaucoma 10 years earlier than Caucasians and are 13 to 17 times more likely to be blind from glaucoma in the 40-to 60-old age group.

P:  Some doctors seem more concerned than others about the intraocular pressure

numbers.  How can we patients know whether our pressures are higher than they should be?

Dr. Rick Wilson:  The normal pressure is between 12 and 22 mm Hg.  However, when people are screened for glaucoma, the IOP of half of them is less than 22 mm Hg.  Therefore, damage can occur at all levels of pressure.  It is very difficult for patients to know whether their pressures are higher than they should be.

P:  How does repeatedly measuring the pressure with a Tonopen affect the pressure?

Dr. Rick Wilson:  Pushing on the eye with the Tonopen  pushes fluid out of the eye.  Therefore, tapping on the eye too long can lower the eye pressure artificially when the readings are taken. 

P:  Are there any new treatments for POAG?

Dr. Rick Wilson:  The Selective Laser Trabeculoplasty (SLT) is a new treatment for glaucoma.  It reality, it is ALT-lite.  That is, a kinder, gentler argon laser trabeculoplasty.  Several medicines are being developed, but none have made it to clinical trials.  A combination of Travatan and timolol (Timoptic) will be introduced soon, but the effect is the same as using Travatan and timolol separately.

P:  Is Lumigan the new medication for treating POAG? 

Dr. Rick Wilson:  No, Lumigan is several years old.

P:  Is any substantive research being done with the objective of repairing the trabecular meshwork so that, someday, current treatments will not be necessary?

Dr. Rick Wilson:  Yes.  That is one of the main objectives of genetic research; that is, to be able to inject the right, corrective genes into the trabecular meshwork through a viral vector, and change the genetic make-up of the trabecular meshwork so that it works normally.

P:  Could stem-cell research help to grow new and better meshwork?

Dr. Rick Wilson:  Possibly.  Yesterday, a group of people who support stem-cell research all called the White House at 11:30 a. m. to urge the President to relax his ban on using any new stem cells.  I was among them as an advocate for glaucoma patients.

P:  Which are the best medicines to open the trabecular meshwork? 

Dr. Rick Wilson:  Unfortunately, the only medicine we have to open the trabecular meshwork is pilocarpine.  The side effects and four times a day dosing limit its appeal.  

P:  Can the eye sometimes get too much fluid, no matter how well the drain works if, for instance, the high pressures are not caused by elevated pressure, but by too much fluid being produced?  

Dr. Rick Wilson:  Yes, that does seem to happen in patients who take systemic steroids, that is, steroids by mouth.

P:  Can being anxious and worried about getting your pressure checked cause the readings to be high?

Dr. Rick Wilson:  Most of my patients think so.  And there is one study that shows intraocular pressures taken after a visual field test are higher than if the test were not taken. 

P:  If ingested steroids seem to increase intraocular fluid production, can naturally elevated steroids do the same?

Dr. Rick Wilson:  Absolutely.  That seems to be part of the reason for the diurnal curve. One study showed that the intraocular pressure was highest when the serum cortisol levels were also at the height of their daily curve.

P:  Nothing's been said about ischemic factors in POAG.  Don't you think some of POAG is really secondary to vascular factors?  For instance, two patients present with IOPs in mid-twenties, but only one of the patients suffers damage to the optic nerve.  Isn't it likely that something besides pressure is harming the optic nerve?  

Dr. Rick Wilson:  Yes.  There are many vascular factors, such as low systemic blood pressure, low blood pressure at night, spasms of blood vessels leading to the eye  -- as seen in patients with migraines.  It may be that the body does not auto-regulate well. Sleep apnea is another subject we have not discussed.  Concern is increasing that sleep apnea may be a strong risk factor for glaucoma.

P:  What percentage of POAG patients benefit from trabeculectomies? 

Dr. Rick Wilson:  Around 90%, according to most studies.

Moderator:  Thank you again, Dr. Wilson.  Goodnight.

End of highlights for July 14, 2004.

On July 21, Dr. Wilson discussed "Glaucoma and High Myopia" in the Chat room. Click here for highlights of that meeting.

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