Chat Highlights
Testing in Glaucoma
July 19, 2000

Norma Devine, Editor

On Wednesday, July 19, 2000, Dr. Rick Wilson, glaucoma specialists at Wills, and the glaucoma chat group discussed "Testing in Glaucoma." 

Dr. Wilson:  Hello all.

Moderator:  Good evening,  Dr. Wilson.  Welcome newcomers and veterans.  Tonight's topic is "Testing in Glaucoma" with Dr. Rick Wilson, glaucoma specialist.  We'll have questions on the topic for the first half  hour or so (until about 9:00 p.m. Eastern time), followed by general questions.

Moderator:  Is it correct to say that testing falls into two categories:  diagnostic and  monitoring?

Dr. Wilson:   Diagnostic has a slightly different meaning than diagnosis. Tests are first designed to detect and diagnose disease, and then it is monitored to make sure there is no progression.  In that regard, you are correct.

Moderator:   How important is it to have dilated pupils when taking visual field (VF) tests? 

Dr. Wilson:   If  patients have a visual field test that is worse than previous ones, and if  their pupils are less than 3 mm Hg, they should repeat the field test with dilated pupils.

P:  What is the standard technique for visual field tests, 30-2, or  24-2? And what is the meaning of the 30 and 24, and what does the 2 mean?  

Dr. Wilson:   The Humphrey Field machine was a copy of a Swiss machine called an Octopus that tested the center of the visual field for 30 degrees in all directions.  The test points were either on the axis of the X and Y (Program 31) or 3 degrees to each side (Program 32).  The latter became the 30-2 when Humphrey copied it over.  A 24 -2 tests 24 degrees from the center of the field temporally and 30 degrees nasally.

P:  Which is better, the 30-2 or 24-2?  How reliable is the 24-2?

Dr. Wilson:   I usually do the 30-2 first and follow patients with the 24-2.  Both are reliable.

Moderator:   Does that mean a 24-2 test would catch damage only when it has progressed further?

Dr. Wilson:   No. It just means the 30-2 gives a better picture of the visual field and the 24-2 covers the important parts that need to be followed.  

P:  I've got macular trauma in the left eye.  Shouldn't the visual field (stimulus) be different, as I can't see the light very well?

Dr. Wilson:   The center of your field should have less sensitivity.

P:  How often should visual field tests be given?

Dr. Wilson:   They should be given every one to two years for glaucoma suspects with good pressures,  yearly for most people with glaucoma, and more frequently for those with more advanced glaucoma.

P:  I have read that the visual field sometimes won't show damage for up to two years because the damage is incremental. If your pressures are relatively decent (mid-teens) and you are seeing no new visual field loss, can you really be reasonably sure that things aren't progressing? Or is it sort of a false sense of security?

P:  If a person's visual field test shows normal, can a doctor say for sure the person has glaucoma?

Dr. Wilson:   One needs to lose 30 to 40% of the optic nerve before changes in the visual field can be seen. Therefore, in the early stage, seeing no change in the visual field could mean damage hasn't reached the threshold to be recognized.

P:  Can you stop the damage, once you see it happening?

Dr. Wilson:   If the pressures are lowered enough, the nerve damage stops and sometimes the nerve health and the visual field even improve.

Moderator:   The other type of testing in glaucoma is the optic nerve itself, yes?  And this is done visually and with photos, or sometimes with the HRT (Heidelberg Retina Tomograph)?

Dr. Wilson:  Right.  Testing in glaucoma is aimed at the appearance of the optic nerve and its functioning, which can be tested with visual field, spatial and temporal contrast sensitivity, and other physiologic tests.

P:  Is HRT a standard test, and when is it performed?  

Dr. Wilson:   The HRT measures the contour of the optic nerve and the nerve fiber layer surrounding the optic nerve.  It is marginally useful for good ophthalmologists, but is more helpful for those who are not as good at looking at nerves.

P:  Is the visual field  test the only way to test for glaucoma?  What other tests are performed  to make sure of a correct diagnosis?

Dr. Wilson:   Usually, an ophthalmologist will find the IOP higher than normal and look at the visual field and the optic nerve.  The optic nerve will show damage first.  The  visual fields, HRT, and GDx will show damage later.

P:  Doesn't the GDx measure the amount of optic nerve fiber loss, if there is any, before the visual field would show anything?

Dr. Wilson:  Yes,  the GDx measures the nerve fiber loss, but how accurately is still a problem.  The  same applies to it as to  the HRT.  Neither modality is good at diagnosing glaucoma, but can be helpful in following glaucoma.

P:  If the HRT and GDx are good for following people who are already known to have glaucoma -- perhaps even have a lot of damage -- are there reasons doctors may elect NOT to use those more advanced tests?

Dr. Wilson:   The cost for themselves and their patients.

P:  What other new forms of testing are being studied?  Is there anything that looks promising?

Dr. Wilson:  We continue to look for objective tests that avoid the subjectivity of the patient.  So far, it is hard to have a test that differentiates the normals from the suspects and those with glaucoma.

P:   Is there a way for patients to measure their own eye pressure, as they measure their own blood pressure?  That would give you doctors an idea of whether there are huge fluctuations in pressure at different times of the day.

Dr. Wilson:  Dr. Drager in Germany is working on a self-eye pressure device.  I don't know whether it is ready for prime time yet.

P:  Wilmer has a home tonometer for measuring your own pressure.

Dr. Wilson:   I haven't seen them report that.  I hope you're right.

Moderator:   On my first visit, the doctor said I had an "afferent defect"-- a difference in how quickly my two eyes responded to a change in light.  He said that indicated optic nerve damage.  Is that a usual test to verify optic nerve damage?

Dr. Wilson:  Yes, it's  low tech; just a penlight, and if the defect is present, that  really tells something about the eye.

P:  In what other eye disease might you find an afferent pupil defect?

Dr. Wilson:   In retinal diseases (a list as long as my lower arm), neurological causes (like tumors pressing on the nerve),  multiple sclerosis, and vascular problems,  like strokes.

Moderator:   Are there any more questions on testing?  We could perhaps also take general questions now?

P:  Dr. Wilson,  I live in Portugal and have been near-sighted since I was 18 years old.  Eight years ago I awoke with a vein block in the left eye, and could see nothing.  I managed to recover some vision, but I lost contrast sensitivity and it's difficult to read without searching.   My doctor told me that was a consequence of the initial glaucoma.  Could my vision get better? I use Timoptic and Trusopt twice a day and my eye pressures are 19 right, 17 left.  The doctor says my nerve is very excavated.  Should I have surgery, or should I try laser first?  Unfortunately, today my wife learned that she has pigmentary glaucoma and her IOP is 39.   Could the contraceptive pill cause that high pressure or make it worse?  The doctor told her she needs surgery.  What about eye drops and laser first?  Thank you very much Doctor and everyone.  I don't feel so lonely now. 

Dr. Wilson:   I'm sorry.  That's a load to carry.  If you have decent vision, then your IOP should be lower if you nerve is excavated.  Medicines or surgery could help.  Laser is not useful unless you are over 50 and have good pigment on the trabecular meshwork (the drain in the eye).  With pigmentary glaucoma, laser can be performed on patients between the ages of 35 and 50, although it still seems to work better on those over 60.  I would try medicines, then laser, and finally, surgery.

P:  I' m sorry but I didn't  understand that very well.  Should IOP be lower with an excavated optic than with a normal optic nerve?  And should my wife stop using the contraceptive pill now that she has learned she has pigmentary glaucoma?

Dr. Wilson:   The IOP should be lower with a damaged nerve.  I don't think I would have your wife stop her birth control pills.  

P:  Doesn't laser close up again in two or three years?

Dr. Wilson:   One kind of laser stops working anywhere from six months to five or more years after the treatment.

P:  I read there is a new short-wave laser that is superior to the argon laser.  Does anyone know anything about this?

Dr. Wilson:  The Selective Laser Trabeculoplasty (SLT) is a wavelength that is  absorbed by the pigment in cells in the trabecular meshwork.  It is safer than conventional laser trabeculoplasty and can be repeated more often, but may be no more effective in the end.

P:  When do you use Holmium laser or do you use it?

Dr. Wilson:   No, not any more.  The Holmium enjoyed a small window of  popularity,  but was not as effective as the usual trabeculectomy.

P:  I had it done when I was 57,  and it did not work. 

P:   Have you found that the length of time laser surgery (trabeculoplasty) lasts in one eye is a predictor of  how long it will last in the other eye? 

Dr. Wilson:   If the laser surgery were done well in the first eye, I would guess that the result should be predictive of  how the second eye would do.

P:  Does a trabeculoplasty damage the fibers holding the lens?  My concern is that if exfoliating patients tend to do poorly in cataract replacement, then damage to fibers holding the lens may not be a good idea in the early days of the disease.

Dr. Wilson:   Trabeculoplasty does nothing to the fibers holding the lens in place.

P:  My husband's laser surgery lasted only one year, when he was 48 or 49 years old.

Dr. Wilson:   Alas, that's  so common. 

P:  What have you heard about the drug memantine to treat glaucoma?

Dr. Wilson:   Memantine is a drug that has been used in Europe for some time to help preserve nerve tissue in neurological disease.  Allergan is conducting trials.  It is very unclear whether it will do any good or not.

Moderator:   I put on sun block for the first time this year and had a strange reaction to this one type.  Is there any chance something in it could be reacting with Timolol?  I am not allergic to anything.

Dr. Wilson:  I haven't heard about that side effect yet.

Dr. Wilson:   I am falling asleep in my chair, so I am going to bid you all a good night and a better week.  See you next week.

Moderator:  Thank you,  Doctor Wilson, for your time and answers.

End of highlights for July 19th chat.

Click here to read more about Testing in Glaucoma.

On July 26th, Dr. Rick Wilson discussed "Genetics and Glaucoma" in the Chat room. Click here for highlights of that meeting.

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