Staging Glaucoma
Chat Highlights
February 26, 2003

Norma Devine, Editor

On Wednesday, February 26, 2003, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Staging Glaucoma."

Moderator:  Welcome back, Dr. Werner.  Last month an Internet problem interrupted our chat about staging glaucoma. Click here to read those chat highlights.  Let's continue discussing the same topic.

P:  What role does disc cupping play in staging?

Dr. Elliot Werner:  The optic nerve head looks a little like a donut.  A rim surrounds a hole in the middle.  The hole is called the cup.  Glaucoma causes the rim to get progressively thinner and the hole to enlarge as the rim is lost.  Enlargement of the central cup, or hole, is called cupping. 

P:  I have normal-tension glaucoma, a loss of fixation in my left eye, and 50% loss of vision.  Does loss of fixation always mean advanced glaucoma?  How does visual field loss compare with optic nerve damage?   What percent of my optic nerve would be damaged?  My doctor is surprised I see as well as I do.

Dr. Elliot Werner:  Generally, glaucoma bad enough to cause loss of fixation is fairly far advanced.  In general, visual field loss and optic disc damage correlate fairly well.  To have detectable visual field loss, you usually have to have lost at least 50% of the optic nerve fibers.

Moderator:  If a person is a glaucoma "suspect," does that mean he or she has early damage or is in the early stage?

Dr. Elliot Werner:  My concept of a suspect is a person with some risk factors, but who does not actually have any glaucoma damage.  Once damage is present, that is glaucoma.

P:  What stage would 90% optic nerve damage be?  

Dr. Elliot Werner:  Some diseases have very formal staging systems.  Mostly, staging is used in cancers of one sort or another, because the treatment and expected outcome depend very much on the stage of the disease.  In glaucoma, there is no formal, agreed-upon staging system, and the treatment does not depend on the stage.  The treatments are pretty much the same regardless of the stage.  A number of staging systems have been developed mainly for research purposes.  These depend upon very specific determinations of the amount of visual field loss and optic nerve cupping.  None are in general clinical use.

P:  My ophthalmologist frequently speaks of  "buying time"  through treatment -- that is, a treatment until it no longer works, then another until that no longer works, then still another.  That gives me the impression that glaucoma progresses relentlessly.  Is it fair to characterize glaucoma like that? 

Dr. Elliot Werner:  Not in all cases.  A recent study, the Early Manifest Glaucoma Trial, found that about 65% of untreated glaucoma patients progressed.  Treatment reduced the risk of progression to about 33%.  It is commonly observed, however, that glaucoma treatments work for a while and then have to be changed, because they no longer control the pressure.

P:  Why do the treatments stop working?

Dr. Elliot Werner:  We don't know.  Another interesting finding of the Early Manifest Glaucoma Trial was that the risk of progression is reduced by 10% for each millimeter of pressure lowering that is achieved with treatment.

P:  I was diagnosed with congenital glaucoma when I was eight months old.  I am 32 years old now.  My previous specialist, who used his fingers to estimate the intraocular pressure (IOP), said it was not possible to get an accurate  reading because of scarring to my cornea.  My IOP would usually run in the 20's, but he said he did not believe the pressure was that high.  My current specialist thinks his readings are accurate.  Which do you think is right?  

Dr. Elliot Werner:  It depends on how much scarring you have.  There are other ways to measure pressure, such as the tonopen, that do not depend so much on a smooth regular cornea.  I would probably believe the doctor who says his pressures are correct.

P:  Is there a time frame over which the disease progresses?  Are there any indicators of what lies ahead?  

Dr. Elliot Werner:  The disease is highly variable from person to person.  Risk factors for progression include age, how much damage is present, damage in both eyes, and the occurrence of small hemorrhages on the optic disc. The Ocular Hypertension Treatment Study (OHTS) found that thin corneas and African-American race were risk factors for progression.

P:  Will reducing IOP in a normal-tension patient stop progression?  

Dr. Elliot Werner:  Not in all cases.  Lowering pressure reduces the risk of progression.  That is an important concept.  Treatment is risk reduction, not a cure.

P:  What percentage of optic fibers have to be present to retain sight?

Dr. Elliot Werner:  That depends on what you mean by sight.  Some useful vision is possible even with less than 10% of nerve fibers remaining.  Normal sight generally requires at least 50% of the nerve fibers to be undamaged.

P:  I seem to recall reading that the character of initial rim notching (thinning) -- to the rim or through the rim -- is an indicator of future damage, and that  notching only to the rim, but not all the way through it, is a more optimistic indicator.  Is that true?

Dr. Elliot Werner:  Incomplete notching is not as much damage as complete notching.  It is generally believed that the more advanced the damage at the time of diagnosis, the greater the risk of future progression.  So you are correct.

P:  What do you factor in more, optic nerve damage, visual fields, or a combination of both?  And how much do you consider what patients think they are seeing?  

Dr. Elliot Werner:  Probably the most important factor in any patient is what they tell you about their vision.  For diagnosis, and in early disease, the optic nerve is more important.  For detecting progression, or in advanced disease, the visual field is more important.

P:  Can you define early, moderate, and severe glaucoma with respect to the visual field?

Dr. Elliot Werner:  The definition of those stages depends on the level of certain numbers in the printout.  "Early" is generally a mean deviation of less the 8 or 10 decibels; "moderate" would be 10 to 20 decibels; and "advanced" would be more than 20 decibels.  That probably is not real helpful, but those are the technical definitions.

P:  What does "end stage" signify?

Dr. Elliot Werner:  End stage usually signifies an eye that has lost useful vision from glaucoma.

P:  I lost significant vision in one eye suddenly and was diagnosed with normal-tension (NTG) glaucoma.  What "stage" of the disease is that?  And, by the way, is it common for those with NTG to lose vision suddenly?

Dr. Elliot Werner:  Sudden loss of vision is very rare in NTG.  If your vision loss is truly from NTG, it probably represents suddenly noticed loss, rather than sudden loss.  If it truly was sudden loss, it probably was due to something else.

P:  Is a glaucoma suspect (ocular hypertensive) in the early stage of glaucoma?

Dr. Elliot Werner:  Strictly speaking, a glaucoma suspect or ocular hypertensive does not actually have glaucoma and would, therefore, not even be in the early stage.

P:  Are nanophthalmic (small) eyeballs staged differently? 

Dr. Elliot Werner:  No.  Any eye with glaucoma would be staged the same.  The treatment might be different, because of the nanophthalmic, but that would not affect how you would quantify the amount of optic nerve damage or visual field loss.

P:  Since it's difficult to see the optic nerve in nanophthalmic eyes, wouldn't the visual field be more important?  

Dr. Elliot Werner:  That's true, but nanophthalmic eyes don't necessarily have smaller optic nerves.  The size of the optic nerve varies tremendously in the population, so the assessment is partly affected by the size of the nerve.  A good clinician will take that into account.

P:  Is aggressive treatment at any particular stage of glaucoma especially effective? 

Dr. Elliot Werner:  In general, you try to achieve the lowest possible pressure in any glaucoma eye without causing harm to the patient.  In eyes that are in the earlier stage, you might tolerate a somewhat higher pressure for a longer time than in an eye that was more advanced and had less vision left to lose.

Moderator:  Thank you for your help, Dr. Werner.  Will you be going to the annual American Glaucoma Society meeting in San Francisco?

Dr. Elliot Werner:  Yes, I am leaving on March 6 and will be back on March 12.  For those of you who are interested, you can see the abstracts of the papers and posters to be presented at the web site of the American Glaucoma Society: www.glaucomaweb.org

End of highlights for February 26, 2003.

On March 5, the glaucoma support group met and discussed "GlaucoTips" in the Chat room. Click here for highlights of that meeting.

Click here for the most recent glaucoma chat highlights and links to the chat archives.

Click here for upcoming glaucoma chat events.