Methods for Clinical Evaluation
Chat Highlights
March 22, 2006

On Wednesday, March 22, 2006, Dr. Jeff Henderer, a glaucoma specialist at Wills, and the glaucoma chat group discussed "Methods for Clinical Evaluation."

Moderator:  Tonight's topic is “Methods for Clinical Evaluation.”  Dr. Henderer, what should a clinical evaluation of glaucoma include?

Dr. Jeff Henderer:  Well, the first step is always to take a history.  That would include information about visual symptoms and family history.  It would also include things like intraocular pressure (IOP) history and diseases such as low blood pressure, migraines, diabetes, and so on.

Moderator:  What's next?

Dr. Jeff Henderer:   The next step is to examine the eye.  You need to look carefully at the nerve to see if glaucoma is present.  Once you have completed the history and examination, then you decide if disease is present and what to do about it.

Moderator:  What are the main tools used in clinical evaluation?

Dr. Jeff Henderer:   The main tools are the doctor's eyes and ears and brain.  Ancillary tools would include the applanation tonometer for measuring the IOP, the visual field test, and perhaps optic nerve imaging.

P:  How do you use your ears in making an evaluation?

Dr. Jeff Henderer:   You have to listen to patients.  If they are telling you they have a problem, they have a problem.  I remember when I was a resident, some of the older residents liked to say that they didn't bother listening to patients.  They would examine them and then tell them what was bothering them.  That's backwards.  The history should guide the examination.  That is especially true in advanced disease, when there is little optic nerve and visual field remaining to follow.

P:   How do you decide which tests are warranted?  Do all suspects need all tests?

Dr. Jeff Henderer:   In my book, all suspects need documentation of their current state.  That means IOP measurements and nerve documentation.  Visual field tests are useful. Other tests, like optic nerve imaging, are very promising, but we don't have enough information to say that they do better than the doctor.

P:   Do you always measure central cornea thickness?

Dr. Jeff Henderer:   I do measure corneal thickness.  It is an important risk factor.  Not because you can "correct" the IOP.  Perhaps you can; perhaps you can't.  There is no nomogram that you can use.  Most of us like to think in terms of "thin," "normal," or "thick".  Thin means higher risk.  Thick means lower risk.  One of the interesting things I heard at the AAO (American Academy of Ophthalmology) meeting last fall was that corneal rigidity, not corneal thickness, per se, might be the most important measurement.

P:   What is corneal rigidity?

Dr. Jeff Henderer:   I confess that I don't have much knowledge of corneal rigidity, other than to say that a "stiffer" cornea is not going to indent as readily with the applanation tonometer.  Therefore, it will cause the IOP to be falsely elevated.  It is probably true that thicker corneas are more likely to be rigid, but not always.  For example, corneal edema might cause a thick cornea that is soft and flexible.  At this time, measuring corneal rigidity is really not possible except in research settings.

P:   How important is gonioscopy?

Dr. Jeff Henderer:   Well, for me gonioscopy is most useful when the patient has glaucoma, and I want to determine which type it is.  For a glaucoma suspect, I'm not thinking of the angle.  For glaucoma patients, though, I am.  Every patient should have gonioscopy.

P:   When a glaucoma suspect comes in with elevated pressures, why aren't you thinking of the angle?  A friend of mine who is a glaucoma suspect with high IOPs was examined today by a glaucoma specialist.  Her pressures were in the teens, not the twenties, her angles were narrow, and she needs laser surgery.

Dr. Jeff Henderer:   Well, I guess it's a bit of semantics. I don't consider a patient with "narrow angles" to be glaucoma suspect.  A narrow angle is an anatomical issue that has nothing to do with glaucoma.  True, narrow angles can lead to an "attack of glaucoma," but there are loads of narrow- angle patients who will never get glaucoma.  I was referring to the patient in whom the optic nerve may be suspicious.  That's the true glaucoma suspect, in my mind.  Sorry about that confusion.

P:   Is it important for the pupils to be dilated during a clinical examination for glaucoma?

Dr. Jeff Henderer:   Dilating the pupils allows a better examination of the optic nerve.

P:   Does dilating the pupils present a problem for pigmentary glaucoma?

Dr. Jeff Henderer:   Pupil dilation does cause pigment to disperse and, in some cases, has been associated with an increase in IOP. In my experience, that's rare.  I think the risk of an IOP rise is vastly outweighed by the benefit to the optic nerve exam.  So I dilate pupils.

P:   Since pupil dilation can be a problem for narrow-angle glaucoma patients, what do you do?

Dr. Jeff Henderer:   Good point.  For the narrow-angle glaucoma patient, it's a judgment call.  If the angle is too narrow (and there is no agreement about what is too narrow), then I don't dilate. I do my best to look at the nerve through an undilated pupil.

P:   Should patients with narrow angles whose pupils are dilated for an examination of the optic nerve have their IOPs checked during dilation?

Dr. Jeff Henderer:   That's not a bad idea.  Some doctors like to see evidence of IOP rise with dilation in order to decide if the angle is narrow enough to treat with laser.  That's not, in my experience, the most common approach.  More commonly, the decision is based on the doctor's educated hunch about what is too narrow.

P:   How often should a patient have a dilated eye exam?

Dr. Jeff Henderer:   I like to perform a dilated eye exam on a patient once a year, and look at the nerve every visit without dilating the pupils.

P:   Can you see the optic nerve more clearly during a dilated eye exam?

Dr. Jeff Henderer:   Sort of.  That can be true if there is a really small pupil (for example, if the patient is using Pilocarpine), or if a cataract is present.  The real reason is that a bigger pupil allows the doctor to use a more powerful lens to get a more magnified, stereoscopic view.

P:   Is it better to take a visual field test while the pupils are dilated or not dilated?  I've taken the tests both ways at the same glaucoma specialist's office.

Dr. Jeff Henderer:   In my experience, it is more important to repeat the visual field tests the same way each time.  That permits the most "apples-to-apples" comparison.  For me, if the patient is on Pilocarpine, I dilate.  Otherwise, I don't.

P:   My eyes and head ache slightly for hours after dilation.  Is that a common complaint or related to glaucoma?

Dr. Jeff Henderer:   If the dilation causes the IOP to go up, that might cause a headache.  The fact that lights are brighter could cause the same problems.  I would not say it's common, nor would I say it's glaucoma.  You'd need to know the IOP.

P:   When my glaucoma became uncontrolled, my ophthalmologist sent me to a glaucoma specialist, but wouldn't give me any records to take along.  He said the glaucoma specialist would want to make his own determination. Is that common?  Although I was a long-time patient of the ophthalmologist, I didn't go back to him.

Dr. Jeff Henderer:   Well, it's hard to know the exact scenario there, but I, personally, like to see those records.  It gives me a sense of the IOP history, and if there are old visual field tests, that helps, too.  Further, the records might give me an impression of the optic nerve from several years ago, and then I can try to determine if change has occurred.

P:   My optometrist's assistant used a portable tonometer recently to measure my IOP.  Are such tonometers accurate?

Dr. Jeff Henderer:   There is a variety of tonometers, which are all pretty accurate within the normal IOP range.  I suppose the most accurate is still the Goldmann tonometer, but sometimes I also use portable tonometry.

P:   Although my visual acuity is measured at each visit to my glaucoma specialist, how often should I see my optometrist for an updated prescription for myopia?  Also, should I expect changes in visual acuity after bilateral trabeculectomies?

Dr. Jeff Henderer:   I suspect that once a year, or two, you should have a refraction.  In general, I don't expect visual acuity changes after surgery.  That's not to say they don't happen, due to a change in the cataract or a change in the relationship of the lens to the cornea after the IOP is lowered.  But, in general, I like to see the visual acuity return to about pre-op levels within a week or two.

P:   After cataract surgery with an IOL (intraocular lens) implanted, is there any reason for visual acuity to change over time in that eye?

Dr. Jeff Henderer:   Tough question. In principle, I would have to say there is no reason for visual acuity to change.  In reality, it can and sometimes does. Why that happens I have never really investigated.  Remember that the lens only accounts for about one-third of the refractive power of the eye.  The cornea accounts for about two-thirds.  Perhaps some corneal changes occur over time in some patients.

P:   How does clinical evaluation differ from 10 or 15 years ago?

Dr. Jeff Henderer:   We haven't talked much about optic nerve imaging.  That's the biggest change in the past 10 years.  These machines have great promise, especially for detecting change.  But we're still trying to figure out the best way to use them.

P:   Is optical nerve imaging the same as HRT (Heidelberg Retinal Tomography)?

Dr. Jeff Henderer:   The HRT is one of three commonly used imaging devices.  The HRT works by measuring the amount of neuro-retinal rim on the nerve.  The other two (the OCT and GDx) work by measuring the amount of nerve tissue on the retina surrounding the optic nerve. We don't know if one is better than the other, so we refer to them all as imaging devices.

P:   Do you think doctors could become too dependent on imaging devices and one day not look at the eye?  The last time I had a refraction, it was done by a machine and a technician.

Dr. Jeff Henderer:   Great point!  I have heard stories about doctors who don't look at the optic nerve and rely solely on imaging.  That's a mistake. Imaging devices can't detect some aspects of the nerve, such as disc hemorrhages and nerve pallor, that can help a doctor decide if disease is present.

P:   Is megalopapilla seen very often by glaucoma specialists?  I read that it is often misdiagnosed as glaucoma.

Dr. Jeff Henderer:   I don't see megalopapilla very often.  It's a congenital variant, and I guess looks like glaucoma, because there is a large cup.  However, that's a normal variant. I certainly see nerves of different sizes, as human beings have big and small nerves, just as we have big and small feet.  The size of the optic nerve is very important to measure and one of the reasons we like the Spaeth disc staging system.

[Editor's Note: See Chat Highlights, February 15, 2006, "Disc Damage Likelihood Scale." http://www.willsglaucoma.org/supportgroup/20060215.htm]

P:   Do nerves differ in size because of the number of cells, or size of cells, or both?  What is optimal?

Dr. Jeff Henderer:   Well, I don't know exactly why nerves differ in size. I guess it's genetic, just as foot size is genetic.  But what I do know is that everyone has roughly the same number of ganglion cells.  The implication is that for people with big nerves, the nerve won't be filled by the cells, while small nerve will be filled.  So big nerves have big cups and small nerves do not.  Calling a big cup "glaucoma" is not possible unless you know the context of the disc size.

P:  I was told that I lost about 50% of my vision.  I have pigmentary glaucoma.  Does that mean I've lost about half of the fibers that make up the optic nerve?

Dr. Jeff Henderer: You might think so, but it's not so. It turns out that we have about a million nerve fibers. We don't need a million, however, to see. In fact, we lose about 5,000 to 7,000 a year just by being alive. Anyway, it turns out that about 40% of the nerves have to be damaged before conventional field tests detect damage. That depends a bit on the location of damage, but it is a rule of thumb.

P: How can we know the percent of vision we have lost?

Dr. Jeff Henderer: That is such a good question that you'd think there'd be an easy answer.   But there is not.  You can base it on the amount of field loss, or the visual acuity (depending on the cause of vision loss).  There is special field test called the Esterman Field that will generate an "efficiency score" that can be plugged into the AMA visual disability guidelines.  They are complicated.  It turns out, for instance, that if you are completely blind in one eye and normal in the other, you are considered something like 75% visually disabled and 24% whole-body disabled.

Moderator: Thank you, Dr. Henderer.  We look forward to your next visit.

Dr. Jeff Henderer:   You're welcome.  Good night everyone.

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