Chat Highlights
Testing in Glaucoma
March 28, 2001

Norma Devine, Editor

On Wednesday, March 28, 2001, Dr. Rick Wilson, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Testing in Glaucoma." 

Moderator:  Welcome Dr. Wilson.  Tonight's topic is "Testing in Glaucoma."  Any questions for Dr. Wilson?

P:  Do you have any suggestions about taking visual field (VF) tests?  Is it best to press the button only when we are sure we see the light? 

Dr.Wilson:  You could drink some coffee so you'll be wide awake.  Hit  the button when you feel reasonably sure you see a light.  Don't listen to the clicks of the machine, and try to keep your eye centered on the target.

P:   Does the VF test or the doctor's examination of the optic nerve reveal more about the condition of the eye?

Dr.Wilson:  Early in the course of the disease, the appearance of the optic nerve reveals more.  The VF test reveals more in advanced cases, especially with regard to progression.

P:   Shouldn't a technician be in the room with the patient taking the test?

Dr.Wilson:   Yes. 

P:  I think a technician should be in the room only if  he or she can keep from rustling papers.  I can't concentrate if there's noise.  

P:  What does a VF test reveal that might cause a doctor to recommend that the patient have surgery? 

Dr.Wilson:  An increase in the scotomas (black areas in the VF field where one does not see well). 

Moderator:  Will visual inspection of the optic nerve always reveal damage that does not yet show up on the visual field test?  

Dr.Wilson:  At least 85% of the time a trained observer of the optic nerve will see signs of damage before the VF test will reveal them.     

P:  I have taken VF tests at different times and places and have had different results.  I even had a different type of field test at Wills which, unlike the others, showed no loss.  How accurate is the test?

Dr.Wilson:  The test is subjective, and has a fair amount of variability.  

P:  I read that the blue-on-yellow VF test may be more sensitive than the white-on-white test.  Is that true?  

Dr.Wilson:  That is true for early glaucoma and early detection of progressive glaucoma. Unfortunately, as is true with all sensitive tests,  there is a lot of noise and variability in  blue-on-yellow perimetry, compared to the white-on-white perimetry.

P:  In a VF  test, does the presence of a cataract  cause those same black areas (scotomas), so that one can't really tell whether the loss of vision is caused by the cataract?  

Dr.Wilson:  A cataract gives a diffuse, almost universal loss of sensitivity, whereas glaucoma gives localized loss.

P:  Why does the test last longer for some patients than for others?  

Dr.Wilson:  There are several different programs, each taking a different amount of time. Each test retests some of the points tested.  If the patient does a poor job giving consistent answers, the test takes a lot longer.

P:  If there are areas on the VF test that are better and areas that are worse, is the test inconclusive?   My doctor says that it's impossible to improve, so she ignored the improved part and focused on the darker area.  From that, she concluded I need surgery.  My IOP pressure is 20.  

Dr.Wilson:  The variability of  fluctuation, which I mentioned earlier,  means some areas are getting better, others are getting worse.  One needs to look at the whole picture.

P:  What do you mean by "the whole picture?"

Dr.Wilson:  By that I mean the overall impression of the VF field.  

P:  In  a VF test, how many decibels (dB) of  Mean Deviation (MD) are considered normal?  How about Pattern Standard Deviation (PSD)?

Dr.Wilson:  Usually less than five dB.  

P:  I was told that my optic nerve is enlarged and cupped.  Is that  a true sign of glaucoma?  I had photos taken only once, a few years ago.

Dr.Wilson:  Yes, the optic nerve is the most common cause for the label "glaucoma suspect."  

P:   How many VF tests are used for a baseline?

Dr.Wilson:  Usually there is a baseline of  two or three VF tests.  

Moderator:  Can two tests taken three months apart accurately show progression of field loss?

Dr.Wilson:  Yes, if  the VF loss is moving ahead rapidly enough.  

Moderator:  Wouldn't the loss have to be quite significant to come to that conclusion? 

Dr.Wilson:  The loss would have to appear to be glaucomatous.  

P:  What do you mean by "glaucomatous?"

Dr.Wilson:  Having to do with glaucoma. 

P:  When would you schedule another VF test after a trabeculectomy? Is it possible for the visual field to improve?

Dr.Wilson:  I would schedule a new baseline VF as soon as the best vision was obtained postoperatively.  And yes, the VF can noticeably improve if there is a significant drop in the IOP. 

P:  During a previous chat it was mentioned that about 35% of the optic new is lost before loss is seen on a VF test. Why, then, give a VF test before that happens?  

Dr.Wilson:  To try to detect the amount of loss at the earliest possible moment. 

P:  How much change in the Mean Deviation (MD) would we expect to see from using a miotic?

Dr.Wilson:  That depends upon how small the pupil got.  I would expect 3 to 6 dB, but don't quote me on that.

P:  In damaged eyes, is it possible that, over time, photographs or HRT (Heidelberg Retinal Tomography) can harm cells? Can they cause an epiretinal membrane?

Dr.Wilson:  I doubt that they would cause an epiretinal membrane.  I also doubt they would cause retinal injury, but cannot categorically deny it.

P:  How often are photos of the optic nerve taken after a patient is diagnosed as a glaucoma suspect?  I was told they are taken every five years.

Dr.Wilson:  I take photos any time I see a change in the optic nerve.  If it is a HRT, then I get it every 12 to 18 months.

P:  Is there a new instrument for measuring intraocular pressure (IOP) using a laser?

Dr.Wilson:  Several new techniques are in the works.  I haven't had any experience with them yet, and they are not on the market.  

P:  How important is it to have photos taken?   I have never had a photo taken, even though my case is not a simple one.

Dr.Wilson:  If your glaucoma is far advanced, photos probably are not important at all.  Photos are important in the early stages.  

P:  My wife's IOP has always been 20 and below.  Now that her pressure measured 22, her doctor wants to start her on eye drops.  Does she need to start taking eye drops?  

Dr.Wilson:  She must have other factors besides IOP.

P:  Can an afferent pupillary defect be detected if the pupils are constricted by pilocarpine?

Dr.Wilson:  Not if both eyes are non-reactive.  If one is reactive, such a defect can be detected.  

P:  What kind of surgery is best for teenagers? 

Dr.Wilson:  A shunt or a trabeculectomy is best for teenagers.

P:  What is the difference between a shunt and a trabeculectomy?

Dr.Wilson:  Take a look at the information on each of those procedures on the Wills glaucoma web pages.  That will tell you more than I can in a short time here.

On April 4, Dr. Wilson discussed "When a Trabeculectomy Fails" in the Chat room. Click here for highlights of that meeting.

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