Visual Fields
Chat Highlights
February 19, 2003

Norma Devine, Editor

On Wednesday, February 19, 2003, Dr. Jeff Henderer, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Visual Fields."

Moderator:  Welcome back, Dr. Henderer.    Tonight we're discussing visual field testing.  

P:  Dr. Henderer, how did ophthalmologists determine progression of glaucoma before automated visual field testing? 

Dr. Jeff Henderer:  I'm not sure there was much to follow. Manual perimetry was a painstaking task, which left checking the optic nerve and intraocular pressure (IOP).  Automated, computerized visual field testing is a big advance.

P:  What are the best light and sound conditions when a patient is taking a visual field test?  

Dr. Jeff Henderer:  Not much light, and even less sound.

P:  Would you please describe the stages of the development of glaucomatous field loss?

Dr. Jeff Henderer:  Usually, the field is affected in the nasal side first. That's good because the other eye can make up for it. The first defect is usually a little blind spot in the far nasal periphery, called a nasal step. That can expand to become an arcuate defect and continue to complete loss of the top or bottom field, called an altitudinal defect. Other variations exist, too.  Sometimes visual field loss occurs close to fixation first.  That might be more typical in normal- tension glaucoma cases.

P:  How do you decide when to perform visual field tests?

Dr. Jeff Henderer:  I perform field tests at diagnosis and at fairly regular intervals during care.

P:  Don't you use a baseline of at least two or three tests?

Dr. Jeff Henderer:  Yes, I like to get two if I'm not sure that I believe the first one.  Sometimes three, but that is not common.  Sometimes you only need one.

P:  One test alone does not really give reliable information, does it?

Dr. Jeff Henderer:  Yes, it can!  But it may not, either.  It can be hard to tell.  Visual field testing is not a perfect science.  Repeating the field test is perhaps the best way to tell.

P:  Is the best way to use the visual field test to look at three, taken a few months apart?

Dr. Jeff Henderer:  That really depends on the person.  Usually that testing frequency is a bit much for people in whom you are not too suspicious of change, because you are likely to see artifact.  Some have argued in theory that three tests a year are optimal, but in reality that doesn't happen much.  I'm not sure it's really needed if you feel things are stable.

P:  My glaucoma specialist said I had too many corrections on my last visual field test and wants to repeat it. He thinks I did not pay enough attention.  I think there was too much noise around me.

Dr. Jeff Henderer:  Yes, that can happen.  The best way to see if a field is different is to compare the most recent one with the first one to see whether a trend is developing. 

P:  Visual fields taken over a period of time can vary significantly, can't they? I have six here for my wife, taken over the past two years.  None are the same and some seem better than the prior ones.  When she had just recovered from the flu, the test results were absurd.  She was tired that day.

Dr. Jeff Henderer:  That is the biggest problem with field tests.  They vary. Therefore, it can be hard to determine which are truly worse.  Fatigue is a big problem, too. That's why you usually need to repeat the test to confirm.  That is a big area of research.

P:  I have secondary glaucoma in my right eye caused by severe trauma to the eye when I was 18 years old.  I was diagnosed just over three years ago at age 45, and my visual fields have been stable since then.  I am using .25% solution of timolol once per day.  A cataract, apparently caused by the same trauma, has been getting worse, to the point where refraction in that eye can be corrected only to about 20/80.  I say "about" because I can make out letters and get some of them, but they are by no means clear.  Is that acuity level bad enough to affect accuracy of the outcome of my visual field test, scheduled for March 17th?

Dr. Jeff Henderer:  Yes, it is. It is likely that you will need to take that into account.  The machine does already.  However, it is possible that eyes with poor central vision will need larger spot sizes to make the test "easier," so that you can get some useful information.

P:  It is my understanding that on the visual field test for glaucoma, visual field loss from other things such a cataracts and macular degeneration is factored out.  Will visual field loss from a worsening cataract show up in the Pattern Standard Deviation (PSD) numbers?

Dr. Jeff Henderer:  Not really.  The pattern plot is supposed to factor this stuff out.  The total plot includes it.  That is, for Humphrey testing and Octopus testing.  Other machines are different.

P:  Is "total plot" the same same as Mean Deviation (MD)?

Dr. Jeff Henderer:  Sort of.  The MD is the number used to "sum" the "abnormality" of the field.  That is akin to the plot on the lower left of the printout, called the total deviation plot.  The PSD is the "sum" of the pattern plot.

P:  If visual field tests are normal, but there's a 40% loss of optic nerve tissue, would that be considered early-stage glaucoma?  I am using two eye drops in the affected eye.  Shouldn't I also be using drops in the fellow eye that, so far, is normal? 

Dr. Jeff Henderer:  That is another big problem with field tests.  The scale is such that early loss is not detected very well.  In general, I only like to treat the eye with disease, but in some situations it might be appropriate to treat a non-affected eye.

P:  Would it be correct to say the visual field test supplies an indication, as opposed to an absolute value, of visual functioning?

Dr. Jeff Henderer:  That's not a bad way to put it.  There is no doubt that the field test does not catch all defects, and even very bad defects are often not totally blind.

P:  I had a visual field test last April, and the print-out showed vision loss corresponding to a blind spot that had developed in one eye.  Last month I had a follow-up field test.  It showed a reduction of the blind spot, corresponding to improvement in vision that I've noticed over the past nine months or so.  My diagnosis was normal-tension glaucoma.  Can you comment, please?

Dr. Jeff Henderer:  Great!  I'm hoping that your vision is improving because you are being treated for glaucoma.  It sounds as if the field test is a good test for you.

P:  Do you take into consideration what the patient feels his or her visual loss is?  

Dr. Jeff Henderer:  Actually, that is one of the first questions asked.  If the patient feels he or she is getting worse, then that means a lot to me, even if the field is stable.  I'm likely to make therapy changes just for that reason.

P:  Does a "red" visual field test track glaucomatous changes or does it only monitor damage caused by taking Plaquenil?

Dr. Jeff Henderer:  Traditionally, that test is used for testing the macula, but there are other colors (blue and yellow) that are supposed to be more effective for glaucoma testing.

P:  Are visual field tests necessary for a patient who has had successful filtering surgery?

Dr. Jeff Henderer:  Personally, I still test,  as "successful" is not a well- defined term.  On the other hand, if I can do no more, then I'm not sure it's useful.

P:  My wife is virtually blind in her right eye.  The last visual field test showed an MD of -27.20 DB.  That's pretty bad isn't it? The PSD was 7.15 DB.  Two years earlier, those numbers were MD of -20.23 DB and PSD of 11.01 DB.

Dr. Jeff Henderer:  That is advanced loss.  Fields of this type are very variable.  Care needs to be taken in calling them worse on the basis of one test.

P:  How many visual fields tests do you need to confirm progressive glaucomatous damage?  Or does it depend on the amount of damage that shows up?

Dr. Jeff Henderer:  Yes, it depends, but if the amount of damage really changes and you see nerve changes, too, then you only need one test.  If it is subtle, then I'd repeat.  Three or more field tests might be needed to say for sure. 

P:  If a patient has problems seeing certain colors, how important is that in testing?  

Dr. Jeff Henderer:  Well, the machine only tests white, red and blue and white and yellow backgrounds.  Loss of color vision is not important for white spots, but can be associated with glaucoma (hence the color testing).  That may be exactly the point of the test.  So, don't worry about the color.  It's much more important to concentrate.

P:  After one eye is patched for the test, how much time is needed to give the patient's other eye time to be ready for the visual field test? 

Dr. Jeff Henderer:  I usually find that by the time the machine has been programmed and all that,  patients are ready for the second eye.  But if you feel that you are not ready, by all means tell the tech and wait.  If you are not comfortable, the test may not be as accurate as you'd like.

P:  How often do you recommend visual field tests for someone with ocular hypertension and no apparent optic nerve changes?

Dr. Jeff Henderer:  That depends on how high the IOP is, and if there is treatment.  In general, I'd say every six to twelve months.  

P:  Is it true that once some of the visual field is lost, it can't be regained?  

Dr. Jeff Henderer:  In general, yes.  However, sometimes with treatment you can "regain" lost field.  Uncommon, for sure, but it happens.

P:  What are the indications in the visual field test of an eye that has had a trabeculectomy that loss is not due to progression of glaucoma?  

Dr. Jeff Henderer:  I suppose the most common reason to lose field after a trabeculectomy, if it is not due to glaucoma, is cataract.  Loss due to cataract typically is characterized by depression on the total plot that is not present on the pattern plot. The pattern plot is a statistical manipulation of the data to correct for that effect.

P:  Yes, but if the pattern plot shows loss, how can it be determined that the loss is not due to glaucoma just by looking at the results of the visual field test?

Dr. Jeff Henderer:  It is the relative amount of loss between the two plots. Loss that is greater on the total plot than the pattern plot is possibly due to cataract. If the two plots are equal, then there is probably no cataract and then it's just glaucoma.

P:  Three years ago I was diagnosed as having normal-tension glaucoma.  My visual field tests are normal, but there are signs of damage to the optic nerve.   I see my doctor every four months, but am not using any glaucoma medications.  So far, I think my vision is stable.  

Dr. Jeff Henderer:  Okay, but remember that visual field tests do not always detect early loss.  Your doctor must be following the optic nerve to see that there is no change.  Good.

P:  Can you have optic nerve damage and a normal visual field?

Dr. Jeff Henderer:  Yes, you can.

P:  I’ve heard references to the “pallor” of the optic nerve, and I’ve read that the pallor of the nerve in ischemic optic neuropathy is different from optic nerve pallor in "garden variety" glaucoma.  Can you say a little about pallor, as well as nerve strokes?  Are you able to differentiate between nerve strokes and other kinds of nerve damage in a general exam of the eye?

Dr. Jeff Henderer:  It can be confusing, since advanced glaucoma leads to rim pallor.  However, there is also loss of the rim.  There are very few eye diseases that cause rim thinning -- loss of tissue -- except glaucoma.  Giant cell (arteritis) is the other main one. Ischemic optic neuropathy gives pallor, yes, but no loss of rim tissue.  That is my main complaint about the idea of glaucoma being a "stroke" of the optic nerve.  In ischemic optic neuropathy you have a condition that really is a "stroke," yet you have no rim thinning!  Why not?  No idea.  There must be something else besides just ischemia at work.  And, yes, you should be able to tell the difference most of the time.

P:  Have any experiments been performed to demonstrate the efficacy of stem cell therapy using visual field testing?

Dr. Jeff Henderer:  Not that I am aware of, but that is a great idea.  Field testing is really the gold standard these days for glaucoma studies.  What the patients sees is what's important.  

P:  Thank you very much, Doctor. I really appreciate your being here in the chat room.

Dr. Jeff Henderer:  You're welcome.  Feel free to e-mail me.

End of highlights for February 19, 2003.

On February 26, Dr. Wilson discussed "Staging Glaucoma" in the Chat room. Click here for highlights of that meeting.

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