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Medical Forum / General / Vision / August 2006Pachymetry as a part of routine comprehensive eye examinations
I spoke with a couple of doctors today at an ocular pathology symposium I would consider to be well-qualified on the subject of glaucoma: o Murray Fingeret, OD (see <http://tinyurl.com/j9uw9> and <http://tinyurl.com/lyk5k>) o Peter Joson, MD (see <http://tinyurl.com/eqaa7>) regarding the discussion we had here a few weeks ago (see <http://tinyurl.com/ejn56>): | Also, a lot of "borderline" glaucoma suspicions can be eliminated by | pachymetry. Very often I get an eyebrow-raising Goldmann tonometry of | 22 but then measure 620 mu corneas. The eyebrow relaxes. | | But I also see a lot of people with 16 mm Goldmann and around 440 mu | corneas. Up go the eyebrows again... I essentially gave them that above example. Both said (as of 8/13/2006) measuring CCT without any other risk factors for glaucoma was nothing they did nor believed should be part of a routine comprehensive eye examination for people who are not ocular hypertensive, not glaucoma suspects (based on other factors than CCT) or glaucoma patients. Dr. Joson said he doesn't take CCTs on every patient he examines. He does on ocular hypertensives and known glaucoma patients who are progressing despite apparent good IOP control. Dr. Fingeret went even further. He has heard of ODs labeling ALL patients with thin corneas a "glaucoma suspect" and having them come back for 6 months glaucoma suspect checks. He basically said that was silly. He also said that even if a patient had pressures of 19 with a CCT of 440 that without any other risk factors, he would not classify such a patient as a glaucoma suspect; he said knowing the CCT tells you nothing in this case. He said the OHTS only showed the usefulness of CCT in known ocular hypertensives, not in patients with normal IOPs. He also said that even if a patient had pressures of 19 with a > CCT of 440 that without any other risk factors, he would not classify > such a patient as a glaucoma suspect; he said knowing the CCT tells > you nothing in this case. He said the OHTS only showed the usefulness > of CCT in known ocular hypertensives, not in patients with normal > IOPs. baloney. the pachymetry would tell you that the true iop is more like 26. hasn't anyone seen the correction tables???? That's almost certainly a glaucoma patient, and is DEFINITELY a glaucoma suspect and an ocular hypertensive. Of course if you don't do pachymetry, well ignorance is bliss... w.stacy, o.d. (what is the reluctance to do a 15 second test once in a patient's lifetime, a test that will enable accurate correction of ALL the goldmann tonometries FROM THEN ON? I don't get it). > He also said that even if a patient had pressures of 19 with a >> CCT of 440 that without any other risk factors, he would not classify [quoted text clipped - 12 lines] > >w.stacy, o.d. I solicited feedback from experts in the field of glaucoma regarding your position. Here are the first ones to come back: Murray Fingeret, OD -- president of the Optometric Glaucoma Society (<http://tinyurl.com/lyk5k>) -- member of The Glaucoma Foundation (<http://tinyurl.com/j9uw9>): "The Current Standard of Care is that Pachymetry is indicated when a risk for glaucoma exists. It is NOT part of the routine, standard, comprehensive examination. Why, because there is not data to explain how we should use corneal thickness measurements in a healthy patient. Until this data exists, nobody has a clue how to interpret and use CCT in a healthy patient. So the idea that you are not meeting the standard of care is crazy. Just the opposite would happen, you would be liable for fraud and doing unnecessary medical testing." (Ouch!) Douglas Anderson, MD -- Chair in Ophthalmology -- Bascom Palmer Eye Institute, Miami, FL -- (<http://tinyurl.com/zq9ew> and <http://tinyurl.com/k8k7c>): "Another way to look at all this is to realize that we may examine a patient to tell whether he already has disease that needs treatment. In another setting we are estimating risk of future disease. So we note age, IOP, disc appearance, and family history as our major risk indicators. You could add CCT, but personally, if all other risk factors are absent, and there is no sign of already developed disease, I'm not in the camp that would advocate CCT." >(what is the reluctance to do a 15 second test once in a patient's >lifetime, a test that will enable accurate correction of ALL the >goldmann tonometries FROM THEN ON? I don't get it). It is unnecessary testing and of unproven significance in 8/2006. Certainly feel free to perform pachymetry as part of *your* routine, standard, comprehensive eye examination. But to bill it to major medical insurance as medically necessary or to imply (or flat out state) it is "standard of care" for a routine eye examination (like checking IOP, pupils, performing ophthalmoscopy, checking VAs, etc.) is not a tenable position in 8/2006 unless you are able to find widely accepted experts in the field of glaucoma support your position. May I offer the following suggestion, which you are certainly free to consider or ignore: Do as I did. When I read your arguments, I disagreed with them. So I solicited the expert opinion of a couple of doctors that are widely considered to be experts in the field of glaucoma in both Optometry and Ophthalmology. I don't think anyone can question the credentials of Dr. Fingeret and Dr. Anderson in the area of glaucoma. >> He also said that even if a patient had pressures of 19 with a >> >>>CCT of 440 that without any other risk factors, he would not classify >>>such a patient as a glaucoma suspect; he said knowing the CCT tells >>>you nothing in this case. If he actually said that, I disagree with him and you, I don't care what his and your credentials are. If you measure a goldmann 26 mm hg "without any other risk factors", would you not consider such a patient as a glaucoma suspect? 26 is what the above person's corrected pressure is. You can't have it both ways. It is NOT part of the > routine, standard, comprehensive examination. I already several posts ago relented on that point. Obviously pachymetry needs only be one once, the first time goldmann tonometry is done, while the eye is still numb, as a calibrating tool for that one and all future ones, and of course once again if corneal laser work is done. You can disagree with that, but don't wave credentials at me. Instead, tell me where my reasoning is off. I say doing golmann tonometry without knowing the corneal thickness is like weighing someone without knowing their height. You'll get a reading all right, but it won't mean much. w.stacy, o.d. [snip] >If you measure a goldmann 26 mm hg "without any other risk factors", >would you not consider such a patient as a glaucoma suspect? We need to be real careful here so there is no confusion: I would not consider a patient who has an "uncorrected" Goldmann tonometry reading of 19mm Hg and no other glaucomatous risk factors besides having a thin cornea (e.g., CCT of 440) to be a glaucoma suspect in 8/2006. Why? For two reasons: 1. Because the OHTS does not make the conclusion that eye doctors should. 2. Because the general consensus of people considered to be experts in the field of glaucoma do not believe I should. > 26 is what the above person's corrected pressure is. Based on some conversion tables you are correct. However, the relevance of this has not been shown to exist in non-glaucomatous/non-ocular HTN patients. [snip] >> It is NOT part of the routine, standard, comprehensive examination. > [quoted text clipped - 3 lines] >one and all future ones, and of course once again if corneal laser >work is done. I should have been clearer here: It is not part of the "standard of case" for the baseline of the routine, standard comprehensive eyecare database. >You can disagree with that, but don't wave credentials at me. I wasn't trying to "wave credentials at you". I was trying to show you that my opinions are not just mine, but consistent with others (I intentionally asked those who are accepted to be experts in the field of glaucoma). I also believe, but don't know for sure without taking a survey, that it is also easily the general consensus of the *vast majority* of experts in the field of glaucoma and probably the vast majority of ophthalmologists. Maybe even ODs too, but I wonder if quite a few ODs have been "brainwashed" by Sonogage? >Instead, tell me where my reasoning is off. Fair enough. It's like I said before -- the OHTS does not come to the conclusion that CCT is a risk factor or that Goldmann tonometry readings need to be corrected for by pachymetry readings in non-glaucomatous/non-ocular HTN patients. It can't because there were no non ocular HTN/non-glaucomatous patients enrolled in that study. You do realize that the OHTS dealt only with ocular HTN/ known glaucoma patients and therefore the fact that CCT was a glaucomatous risk factor in those ocular HTN patients that developed glaucoma cannot be extrapolated or proven to exist in people outside of that population (i.e., "healthy patients")? >I say doing golmann tonometry without knowing the corneal thickness is >like weighing someone without knowing their height. You'll get a >reading all right, but it won't mean much. In ocular HTN and glaucoma patients, you are correct. However, no proof exists that such "correction" is relevant or important in "healthy eyes" and therefore performing such testing is not proven to be indicated in 08/2006. The problem is that you don't recognize your example of a 19 mm Hg Goldmann patient with 440 mu corneas as being ocular hypertensive. Maybe the ohts study and your experts didn't either. So be it. You are all wrong. It is not exactly rocket science to place the above patient in the oh category by definition. Sorry, I attended Berkeley. I always challenge authority. And I do believe that although pachymetry is not required by all "authorities" at this time, it soon will be. w.stacy, o.d. > The problem is that you don't recognize your example of a 19 mm Hg > Goldmann patient with 440 mu corneas as being ocular hypertensive. [quoted text clipped - 9 lines] > > w.stacy, o.d. Hogwash. If pachymetry is vitally important in glaucoma diagnosis, why not have GDx, HRT, or OCT become the "standard of care"? After all, isn't nerve fiber loss the key and most important sign that something isn't right? Except before nerve fiber imaging, it was field loss as the diagnostic key. Except before automated fields, it was ONH rim defect that was the key. Except before fundus/ONH photos it was elevated pressure that was the key. And that, doc, is the answer. Something isn't right and that doesn't mean that a pressure of 19 or for that matter 26 is the problem. With or without pachymetry. My corneas are, for whatever strange and variant anatomical build, are unequal. My pressures *are* equal and 16. Pachy corrected, one was 19. GDx with latest software "found" a sector with enough loss to flag it. HRT and OCT did not. Fields did not. ONH photo did not. GDx with older software did not. I'd guess the "flaw" is in the software or installed comparative database. My situation was initially to *test* the new GDx protocols at a conference. If GDx was done and nothing else, I would be labeled "suspect" or "glaucoma---rx drops". If pachy was done and nothing else, I would be a "suspect". If then OCT or HRT was done, I would be off the hook. I could go on with various scenarios but the bottom line is that no single test yields the answer. I will maintain, however, and this is strongly supported by the "experts" that pressures are for the most part useless in the diagnosis of glaucoma. Now with our latest tools, even following pressures during treatment may be useless. How much reduction is enough? It's really just a guess, isn't it? If got dozens of patients with pressures in the mid twenties for years with absolutely no detectable pathology. What about LASIK'd people ? Nicely thinned and altered topograhpy corneas, so no need for tonometry there. What about the 60mmHg suction ring pressure---did that cause any nerve fiber loss that one day, along with age related loss might trigger a GDx "you've got glaucoma" report? Anyone ever try to figure that out? For me, I'll just keep on doing regular old tonometry because "it's the way it's done", dilated fundus exams with a really good ONH eval, FDT or Matrix fields on every patient and refer the suspects to a colleague with lots of experience and with NFL imaging machine. Heck, I might as well get a pachy----I really do like new toys. LB, O.D. > Heck, I might as well get a pachy----I really do like new toys. You really should, if you're doing goldmann tonometry, as the handy little correction table gives you more confidence in the readings. I do know that iop has fallen into low esteem of late, but it is still standard of care. So if you're going to do it, you might just as well know what the pressures are corrected for corneal thickness (ranges from +7 to -7 mm Hg correction in corneas from 445 to 745 mu). For really thick or thin corneas you can extrapolate for even larger corrections. And a pachymeter is cheap and easy to use (easier for me than goldmann tonometry) w.stacy, o.d. >If pachymetry is vitally important in glaucoma diagnosis, why not have >GDx, HRT, or OCT become the "standard of care"? Please clarify. If you are talking about ocular hypertensives and glaucoma patients, those tests are the "standard of care" as part of their baseline workup and periodically thereafter to assist in the diagnosis and management of glaucoma/glaucoma suspects as far as I am concerned. I routinely perform objective optic nerve head (ONH) analysis (HRT) and objective retinal nerve fiber layer (RNFL) analysis (EITHER GDx/VCC OR OCT -- NOT BOTH) on all my glaucoma suspects and many of those with other forms of optic neuropathies. (Aside: I would love to have GDx/VCC and OCT BOTH, but insurance companies would nail me if I did that routinely.) If you are talking about routine, comprehensive eye examinations in "healthy patients", then the number one reason these aren't is the unfavorable benefit-to-cost on the health care system to implement these tests to screen "healthy patients". The gold standard for glaucoma diagnosis continues to be (as it has been "forever") stereoscopic evaluation of the ONH and RNFL via fundus photography. Most of the time what these objective tests do is confirm my diagnosis based on fundoscopy or draw my attention to re-evaluate particular parts of the ONH or RNFL. IOW, when these tests come back suggesting pathology, I look where they suggest the problem is based on anatomy. If there is NO optic nerve/RNFL disease there, I give little weight to the results. If there is definite disease, it confirms what I saw. If the ONH/RNFL is questionable, then the results of those tests might be what convinces me to recommend or not recommend treatment. BTW, these objective tests will hopefully end up being a Godsend when it comes to glaucoma suspects/patients with ONH anomalies like severly tilted discs who are poor visual field takers.. >After all, isn't nerve fiber loss the key and most important sign that >something isn't right? That's current thinking, but objective RNFL isn't as sensitive in 8/2006 as a trained doctor who stereoscopically evaluates the ONH and RNFL via funduscopy and fundus photography. >Except before nerve fiber imaging, it was field loss as the diagnostic >key. [quoted text clipped - 3 lines] >Except before fundus/ONH photos it was elevated pressure that was the >key. True. When I started managing glaucoma, everyone with IOPs over 21 pretty much got treated. >And that, doc, is the answer. Something isn't right and that doesn't >mean that a pressure of 19 or for that matter 26 is the problem. With or >without pachymetry. Current thinking on IOP is basically this: IOP is something we need to consider lowering when progressive glaucomatous optic neuropathy occurs. It is the ONLY risk factor we as doctors can influence to reduce the risk of progression. >My corneas are, for whatever strange and variant anatomical build, are >unequal. My pressures *are* equal and 16. Pachy corrected, one was 19. We also need to remember that the reason we correct Goldmann tonometry via CCTs is not that CCT directly influence Goldmann tonometry. Corneal rigidity does (we think). We measure corneal rigidity *indirectly* via by measuring CCT. We don't know if everyone with the same CCT has the same corneal rigidity. Just like people have different textures of skin, different propensities to scar. >GDx with latest software "found" a sector with enough loss to flag it. >HRT and OCT did not. Fields did not. ONH photo did not. GDx with older >software did not. I'd guess the "flaw" is in the software or installed >comparative database. Or maybe you have extremely early RNFL loss that wasn't there 10 years ago. Or maybe you were born with a lack of RNFL there congenitally. Or maybe it's an artifact. See, now by running this test on yourself, you are now going to be, if in your mind only, a glaucoma suspect for life. You are not gonna be able to sleep and constantly worry :) Even if everything else is perfect, you will always have that thought in the back of your head. >My situation was initially to *test* the new GDx protocols at a >conference. If GDx was done and nothing else, I would be labeled >"suspect" or "glaucoma---rx drops". If pachy was done and nothing else, >I would be a "suspect". If then OCT or HRT was done, I would be off the >hook. Right. I personally continue to advocate the community accepted standard of care to screen for glaucoma in patients presenting for routine comprehensive eye examinations. No need to unnecessarily "brand" someone a glaucoma suspect. >I could go on with various scenarios but the bottom line is that no >single test yields the answer. I will maintain, however, and this is >strongly supported by the "experts" that pressures are for the most part >useless in the diagnosis of glaucoma. For the most part, true -- IOP is merely a risk factor. A risk factor whose risk increases the higher the IOP goes. At some point, we decide to treat pressures rather than progressive glaucomatous optic neuropathy. >Now with our latest tools, even following pressures during treatment >may be useless. Pressure reduction is, of course, vitally important because it is the only risk factor we, as eye doctors, can influence. >How much reduction is enough? It's really just a guess, isn't it? Yes, it is. We have ideas and guidelines, but no a priori knowledge of the amount of pressure reduction is the minimum necessary to maintain good visual function and quality of life for an individual patient's lifetime. [snip] Excellent and timely discussion, eh? My additional comments follow. I've cut some of your post leaving that which keeps the flow. Clearly we mostly agree and your obviously provide an appropriate and competent level of care. I have chosen to not delve so deeply into glaucoma treatment mostly because my patient base is (thus far) low risk, my bank account can't handle the RNLF scanners' costs and in our small community we have some excellent glaucoma specialists OMDs with the appropriate tools to do right by the patient. I've learned much from them directly through doctor-to-doctor education and patient follow up care. > I routinely perform objective optic nerve head (ONH) analysis (HRT) > and objective retinal nerve fiber layer (RNFL) analysis (EITHER [quoted text clipped - 8 lines] > unfavorable benefit-to-cost on the health care system to implement > these tests to screen "healthy patients". And that is because super-critical screening will result in flagging an unnecessarily larger group of people as suspects who do not require treatment or even follow up. To pick up one person who will develop glaucomatous field loss, perhaps thousands of people will undergo extensive testing (read: $$$) to find out nothing is wrong. (Numbers made up for discussion.) Surely that's worth it for the one person, but should society have to absorb the costs? > The gold standard for glaucoma diagnosis continues to be (as it has > been "forever") stereoscopic evaluation of the ONH and RNFL via fundus > photography. The manufacturers of the RNFL scanners would disagree. ;-) > >After all, isn't nerve fiber loss the key and most important sign that > >something isn't right? > > That's current thinking, but objective RNFL isn't as sensitive in > 8/2006 as a trained doctor who stereoscopically evaluates the ONH and > RNFL via funduscopy and fundus photography. We thought is was in 12/05 but then the normative database snuck in some false positives. Is it the machine or the software that's the problem? Wouldn't it be nice to objectify the definitive diagnosis? But I do agree with your statement. > Current thinking on IOP is basically this: IOP is something we need > to consider lowering when progressive glaucomatous optic neuropathy > occurs. It is the ONLY risk factor we as doctors can influence to > reduce the risk of progression. What ever happened to analysis of capillary profusion and treatment to address that as the risk factor to manipulate? And which comes first, degradation of profusion causing something to elevate IOP or IOP that causes something to reduce capillary profusion? > We also need to remember that the reason we correct Goldmann tonometry > via CCTs is not that CCT directly influence Goldmann tonometry. > Corneal rigidity does (we think). We measure corneal rigidity > *indirectly* via by measuring CCT. We don't know if everyone with the > same CCT has the same corneal rigidity. Just like people have > different textures of skin, different propensities to scar. Hence what is the value of pachymetry if we don't know the answers to the above? > Or maybe you have extremely early RNFL loss that wasn't there 10 years > ago. Or maybe you were born with a lack of RNFL there congenitally. [quoted text clipped - 3 lines] > in your mind only, a glaucoma suspect for life. You are not gonna be > able to sleep and constantly worry :) Nope. Software error. Gotta be! I'd bet on anatomical anomaly. > >I could go on with various scenarios but the bottom line is that no > >single test yields the answer. I will maintain, however, and this is [quoted text clipped - 19 lines] > of pressure reduction is the minimum necessary to maintain good visual > function and quality of life for an individual patient's lifetime. You'd think by now we would. But when we consider that the diagnosis and treatment/management of glaucoma has so radically changed in only the last 5-10 years, it would be awesome if we could understand the root cause and influence that. Thanks for this interesting discussion (devoid of Otis and Ace---yeah!). I wonder how much of this gets to the average reader. --LB, O.D. >Excellent and timely discussion, eh? My additional comments follow. >I've cut some of your post leaving that which keeps the flow. Sure -- sounds good. >Clearly we mostly agree and your obviously provide an appropriate and >competent level of care. I have chosen to not delve so deeply into [quoted text clipped - 4 lines] >from them directly through doctor-to-doctor education and patient follow >up care. I am in a large urban area where there are a lot of OMDs and even glaucoma subspecialists. However, I am still trying to be as heavily involved in the evaluation, management and treatment of glaucoma as my comfort level and the laws of the state of California allow me to. [snip] >> The gold standard for glaucoma diagnosis continues to be (as it has >> been "forever") stereoscopic evaluation of the ONH and RNFL via fundus >> photography. > >The manufacturers of the RNFL scanners would disagree. ;-) Why am I not surprised? >Wouldn't it be nice to objectify the definitive diagnosis? But I do >agree with your statement. Yes it would. When I see glaucomatous optic neuropathy and those objective imagers confirm it, I feel good. And I think they might be great at picking up subtle progression (haven't seen hundreds of patients so I can't say), but for diagnosis of glaucoma they still could use a lot of improvement. >> Current thinking on IOP is basically this: IOP is something we need >> to consider lowering when progressive glaucomatous optic neuropathy [quoted text clipped - 3 lines] >What ever happened to analysis of capillary profusion and treatment to >address that as the risk factor to manipulate? I think mainstream eye doctors don't believe those objective laser Doppler flowimeters have proven to be sufficiently useful in the management of the vast majority of glaucoma patients, unlike HRT, GDx and OCT. >And which comes first, degradation of profusion causing something to >elevate IOP or IOP that causes something to reduce capillary >profusion? I believe the its the latter, but what do I know? In the vast majority of open-angle glaucoma (OAG) I think the vasogenic hypothesis of glaucoma makes the most sense (versus structural). >> We also need to remember that the reason we correct Goldmann tonometry >> via CCTs is not that CCT directly influence Goldmann tonometry. [quoted text clipped - 5 lines] >Hence what is the value of pachymetry if we don't know the answers to >the above? The value of pachymetry is we KNOW than thin corneas (for whatever reason) are significant risk factor for the progression from OHTN to glaucoma. We KNOW that even after compensating for the false low Goldmann tonometry readings we get with thin corneas, that even then it is a risk factor. IOW, an OHTN with THICK corneas with CCT-adjusted Goldmann tonometry readings of 27 has a lower risk of progressing to glaucoma than an OHTN with THIN corneas with a CCT-adjusted Goldmann tonometry readings of 27. We don't know WHY, but we know it DOES. Discovering WHY makes great research, but knowing it DOES makes great clinical care. >> Or maybe you have extremely early RNFL loss that wasn't there 10 years >> ago. Or maybe you were born with a lack of RNFL there congenitally. [quoted text clipped - 5 lines] > >Nope. Software error. Gotta be! I'd bet on anatomical anomaly. For curiosity's sake, I would repeat the GDx several times to verify its repeatability on your eye. If it is PRECISE, then follow serially for a couple of years with repeat GDxs. If it changes, suspect progression. If its stable, suspect stability (or progression so slow you may die of old age before you develop subjective visual dysfunction.) See what you got for running GDx on yourself! :) [snip] >> We have ideas and guidelines, but no a priori knowledge of the amount >> of pressure reduction is the minimum necessary to maintain good visual [quoted text clipped - 7 lines] >Thanks for this interesting discussion (devoid of Otis and Ace---yeah!). >I wonder how much of this gets to the average reader. Anytime. >>>We also need to remember that the reason we correct Goldmann tonometry >>>via CCTs is not that CCT directly influence Goldmann tonometry. >>>Corneal rigidity does (we think). We measure corneal rigidity >>>*indirectly* via by measuring CCT. Seems self-contradictory. As you said above, "we correct Goldmann tonometry via CTTs". And we do it according to the following table: Corneal Thickness Add to (+) or subtract from (-) Raw Goldmann 445 (microns) +7 460 +6 475 +5 490 +4 505 +3 515 +2 530 +1 545 0 560 -1 575 -2 585 -3 600 -4 615 -5 630 -6 645 -7 If the powers that be in the eye industry don't make these corrections BEFORE labeling a person such things as "ocular hypertensive" or "borderline glaucoma", they should be. BTW, it is not exactly rocket science nor is it some "unknown" personal corneal rigidity factor. Consider two balloons made of the same rubber material and inflated to the same internal pressure. The rubber is 1 mm thick in the first say 6 mm thick on the second. To flatten a given area of the second balloon is going to take more pressure than the same are on the first, no? w.stacy, o.d. >>>>We also need to remember that the reason we correct Goldmann tonometry >>>>via CCTs is not that CCT directly influence Goldmann tonometry. >>>>Corneal rigidity does (we think). We measure corneal rigidity >>>>*indirectly* via by measuring CCT. > >Seems self-contradictory. Not at all. >As you said above, "we correct Goldmann tonometry via CTTs". First of all, were you "correcting" Goldmann IOP measurements prior to the results of the Ocular Hypertension Treatment Study (OHTS) being made known? That being asked, now... In ocular hypertensives (OHTNs), we correct Goldmann tonometry per CCTs as a risk factor for them developing glaucoma. I don't use pachymetry correction cards. I merely remember "thin corneas" are at greatest risk. >And we do it according to the following table: [snip] Why do you use those? There are at least three, all of which are different and each of which have been published in peer-reviewed journals: Dougherty's (2000), Ehler's (1975), and Whitacker's (1997). What makes "yours" right? >If the powers that be in the eye industry don't make these corrections >BEFORE labeling a person such things as "ocular hypertensive" or >"borderline glaucoma", they should be. Based on what? As I wrote, the definition of OHTN (IOP >21 without evidence of glaucomatous optic neuropathy) was defined long before the OHTS. And that IOP was defined as based on that obtained from UNCORRECTED Goldmann tonometry readings. Please present evidence, preferably in the form of peer-reviewed studies or even opinion from someone who the general ophthalmic community would consider as an expert, to support this premise -- that we should make these corrections PRIOR to labeling someone OHTN? I don't even need that. If you can tell me that based on your anecdotal personal experience managing hundreds of glaucoma patients that this has become clear to you or you've personally observed a trend over time -- that is, that that information resulted in less progression of your patients' glaucomatous optic neuropathy, less false positives (treating people that really didn't have glaucoma) and less false negatives (not treating people that really did have glaucoma), I'll give some weight to that even... What I won't give weight to is theoretical, sounds good on paper, just makes sense, wild theory, or propoganda from companies whose goal it is to sell pachymeters, based on no real world solid proof. >BTW, it is not exactly rocket science nor is it some "unknown" personal >corneal rigidity factor. Consider two balloons made of the same rubber >material and inflated to the same internal pressure. The rubber is 1 mm >thick in the first say 6 mm thick on the second. To flatten a given >area of the second balloon is going to take more pressure than the same >are on the first, no? No. A cornea is not a piece of CR-39. All corneas are not made of exactly the same stuff. That's one of the reason we can't exactly predict the results of refractive surgery. More importantly, you fail to realize that the measurement of intraocular tensions via Goldmann tonometry is not as precise as you apparently make it out to be. It is, at best, imprecise -- an estimate -- with a lot of noise, especially when we are dealing with a single measurement on an individual patient. Many factors affect IOP including instrument calibration, technique, corneal curvature (+/- 2mm Hg), corneal hydration, corneal thickness (+/- 3mm Hg commonly) and corneal rigidity (via Young's modulus -- +/- 17mm Hg!!!!). P.S. No need for me to reinvent the wheel -- Much of this above information was shamelessly stolen from the August 2006 (Volume 11; Number 6) Primary Care Optometry News article entitled "Classify corneas simply as average, thin or thick" that begins on p.36. Any of you guys going to VisionExpo West in <1 m, or the Academy meeting in 12/2006 in Denver, CO??? >First of all, were you "correcting" Goldmann IOP measurements prior to >the results of the Ocular Hypertension Treatment Study (OHTS) being >made known? > no, just since I've had the pachymeter, about 2 years. >Why do you use those? > [quoted text clipped - 5 lines] > > I simply use a published card. I'm not sure what you're getting at. Surely any correction is better than no correction, and while your thick, thin or normal notion is better than no information, it's not as good as any calibration table. >>If the powers that be in the eye industry don't make these corrections >>BEFORE labeling a person such things as "ocular hypertensive" or [quoted text clipped - 9 lines] > > Thanks, since as you probably well know, one doesn't exist. >What I won't give weight to is theoretical, sounds good on paper, just >makes sense, wild theory, or propoganda from companies whose goal it >is to sell pachymeters, based on no real world solid proof. > > Well mine is a combo of the first three plus my experience, which has been that corneal thicknesses vary A LOT, and very often, I am set at ease or alarmed by my pachymetry readings (very thick or very thin, respectively). >All corneas are not made of exactly >the same stuff. That's one of the reason we can't exactly predict the >results of refractive surgery. > > Pretty much the same stuff, unless you can point me toward a peer reviewed article that shows significant differences in chemistry or physical structure among normal healthy unoperated on corneas. >More importantly, you fail to realize that the measurement of >intraocular tensions via Goldmann tonometry is not as precise as you [quoted text clipped - 3 lines] > > Oh I understand that well, and one of the biggest errors is unusually thin or thick corneas. Most of the others are operator error, in my experience, because my tonometry reading over the years for many patients are boringly enough usually within 1 or 2 mm. In fact if I had to give up doing tonometry or pachymetry on people with no known glaucoma risk factors, I'd probably give up the tonometry. >>First of all, were you "correcting" Goldmann IOP measurements prior to >>the results of the Ocular Hypertension Treatment Study (OHTS) being >>made known? >> >no, just since I've had the pachymeter, about 2 years. Why only ~2 years ago? We've known for dozens of years that Goldmann applanation tonometry was affected by CCT. We've had correction tables for at least 20 years! It's obvious. You got one and use one based on the OHTS. The "problem" is you draw unproven conclusions from the OHTS. The OHTS determined CCT is a risk factor in "traditionally" defined ocular hypertensives (OHTN) progressing to glaucoma, not in normotensive patients. There is (AFAIK) absolutely no proof, consensus of expert opinion or strong evidence one should "correct" Goldmann tonometry readings in normotensive patients or use this information to determine whether one is falsely labeled normotensive. >>Why do you use those? >> [quoted text clipped - 8 lines] >thick, thin or normal notion is better than no information, it's not as >good as any calibration table. I disagree. I look at the CCT in OHTNs and base the risk factor on the thickness. This is supported by the results of the OHTS and the expert opinion of glaucoma experts -- people who have treated hundreds of glaucoma patients are in all likelihood in a far better position than you to judge whether this is true or not. You take Goldmann applanation tonometry readings and apply a conversion (which may or may not be accurate) based on CCT in ALL patients to create a inexistant "precise" reading. This is not supported by the OHTS nor the expert opinion of glaucoma experts. >>>If the powers that be in the eye industry don't make these corrections >>>BEFORE labeling a person such things as "ocular hypertensive" or [quoted text clipped - 9 lines] >> >Thanks, since as you probably well know, one doesn't exist. Right. So you have nothing to you point me to to support your belief that eyecare doctors should "correct" Goldmann IOPs based on CCT in classically defined non OHTN patients. >Well mine is a combo of the first three ("theoretical", "sounds good on paper" and "just makes sense".) >plus my experience which has been that corneal thicknesses vary A LOT, >and very often How does the fact that corneal thickness vary a lot mean it is clinically revelant or important for doctors to make that adjustment? >I am set at ease or alarmed by my pachymetry readings (very thick or >very thin,respectively). In OHTNs, they should, to a point, because that of the OHTS conclusions. [snip] >In fact if I had to give up doing tonometry or pachymetry on people with >no known glaucoma risk factors, I'd probably give up the tonometry. That is silly. Asymptomatic patient "A" comes in CCTs of 560, consistent IOPs of 45. This patient would never get worked up until there was obvious glaucomatous optic neuropathy which a huge percentage of patients like this would develop. If you checked IOPs on this person, you could/would have lowered the pressure a lot earlier than waiting for frank nerve damage. Asymptomatic patient "B" comes in CCTs of 430, IOPs of 10. These patients would undergo needless glaucoma workups costing potentially thousands of dollars and in all likelihood these patients would never develop glaucoma. Yes, I don't do pachymetry on people with no known glaucoma risk factors. And I sleep well at night knowing that the ophthalmic community in general considers that care to be proper in 8/2006. Of course, I am willing to change my position. I'll follow the literature and listen to the advice of experts in the field of glaucoma and eye care. I am just waiting for someone to give me a good reason to do so. >Yes, I don't do pachymetry on people with no known glaucoma risk >factors. And I sleep well at night knowing that the ophthalmic [quoted text clipped - 7 lines] >I am just waiting for someone to give me a good reason to do so. > That's what I tried to do, obviously unsuccessfully. I'm calling this another dead horse discussion. Sleep well w.stacy, o.d. i think your arguments are strong, but i think in the end the comments of Larrydoc summarize my feelings on this subject. nowadays it is almost essential that everyone have a pachymeter. it happens so often that i see a patient with borderline pressures that i need to use a pachymeter daily on many many patients. but not every patient. what about a teenage kid with C/D of 0.1 and pressures of 12 OU? for that patient their risk of having glaucoma is virtually nil. even the teenage kid with a C/D of 0.3 and pressures of 19 doesn't seem to me to be at such a risk that i need to use pachymetry. so i wouldn't argue that pachymetry should become a "prelim" test that must be done on everyone, but i would say that its use should be routine in any office. and i would go further by saying that some form of nerve fiber layer analysis ALSO must be available in any office that claims they are treating glaucoma. in my view if a doctor is claiming to offer glaucoma treatment without a nerve fiber analyzer and without a pachymeter (i.e. using only a visual field analyzer) then they need to realize that the field has changed dramatically and they are no longer offering standard-of-care treatment. although pachy's are cheap, a nerve fiber layer analyzer is not and its a bitter pill to swallow but reality is reality. glaucoma is a tough diagnosis to make and the recent technology has proven itself to be quite helpful in weeding out individual variability and getting at difficult measurements. i didn't attend berkeley but i too tend to think a little independently. i couldn't look at myself in the mirror and claim that i was a good glaucoma doctor unless i routinely utilized pachymetry and nerve fiber analysis. but pachymetry on everyone isn't necessary but IT IS if you at all suspect they could be a glaucoma suspect. maybe thats all you were saying to begin with, in which case i would agree. ========== > The problem is that you don't recognize your example of a 19 mm Hg > Goldmann patient with 440 mu corneas as being ocular hypertensive. [quoted text clipped - 9 lines] > > w.stacy, o.d. > so i wouldn't argue that pachymetry should become a "prelim" test that > must be done on everyone, but i would say that its use should be > routine in any office. Certainly not a prelim test on every exam, since in only needs to be once in a lifetime (plus once following keratomilieusis) as a calibration for the initial and all subsequent goldmann tonometries (and all previous tonometries on that patient). w.stacy, o.d. >i think your arguments are strong, but i think in the end the comments >of Larrydoc summarize my feelings on this subject. [Let's get this out of the way first: When I speak of OHTNs, I am talking about those that meet the classical definition of having IOPs >21 via uncorrected Goldmann tonometry without evidence of glaucomatous optic neuropathy.] >nowadays it is almost essential that everyone have a pachymeter. it >happens so often that i see a patient with borderline pressures that i [quoted text clipped - 7 lines] >must be done on everyone, but i would say that its use should be >routine in any office. I can't argue with you there. There are a lot of ocular hypertensives (OHTNs) out there and it is clear that "thin corneas" (either directly or indirectly) are a strong risk factor in predicting which of these OHTNs will develop glaucoma. >and i would go further by saying that some form of nerve fiber layer >analysis ALSO must be available in any office that claims they are [quoted text clipped - 7 lines] >recent technology has proven itself to be quite helpful in weeding out >individual variability and getting at difficult measurements. I don't think a doctor should have to necessarily have an objective retinal nerve fiber (RNFL) imaging/analysis device (i.e., GDx/VCC or Stratus OCT) in their office. Rather I would say this equipment should be *available* to any doctor who chooses to care for ocular hypertensives, glaucoma suspects and clear cut glaucoma patients. Most neurologists don't own their own MRI, but use one routinely. Rhetorical question: Why? Rhetorial answer: Cost. Same with me. Why don't I own a HRT, GDx or OCT? Cost. I can't justify the (I'm just guessing here) $1,000 - $3,000/month lease payment on these things. Plus, technology is changing rapidly and I don't want to be stuck with costly device that will potentially be non state-of-the-art in 4 years. Case in point, we are now at HRT3. I wouldn't want to be using an HRT1 or antiquated scanning laser ophthalmoscope (circa 1994) on my 2006 patients. So when I need these tests done, I send the patients to a clinic where I have pachymetry, along with modern objective RNFL imaging, objective ONH imaging, and fundus photography perfomed. Pachymetry needs to be done only once (typically) and the other tests I have perfomed yearly (typically), and sending my patients < 8 miles away once a year makes a lot more financial sense to my office than purchasing/leasing said equipment. If HMOs weren't so prevelant around here, and if I wasn't only within the last year glaucoma certified in the state of California, things might be different. You have to be following more glaucoma patients than I am for it not to be a financial mistake. [snip] >The problem is that you don't recognize your example of a 19 mm Hg >Goldmann patient with 440 mu corneas as being ocular hypertensive. Where is the evidence that we should? Have you been measuring CCT routinely before the results of the Ocular Hypertension Treatment Study (OHTS) were released? It has been common knowledge for dozens of years before the Ocular Hypertension Trial Study (OHTS) that corneal rigidity (indirectly related to corneal thickness) was something that was considered to be relatively unimportant. The OHTS changed that. One of the conclusions came to is CCT was a statistically significant risk factor in those ocular hypertensives (OHTN) than developed glaucoma. Therefore, CCT should be measured in all ocular HTNs. From the study conclusions (emphasis mine -- see <http://tinyurl.com/k663w>): "a multivariate risk factor analysis of the trial results indicated that increased IOP, age, cup-to-disc ratio and thin corneas were all risk factors for the development of primary open-angle glaucoma among *ocular hypertensive patients*." Therefore, in OHTNs, the following needs to be remembered: "Corneal pachymetry, meanwhile, is useful not only in identifying those who have thin corneas - the strongest risk factor in the study - but also in determining the patients true IOP. Thinner corneas are less resistant to applanation instruments. In eyes with such corneas, tonometry can fail to detect the imbalance between the inflow and outflow of the aqueous humour which would be measured as an increased IOP in an eye with normal corneal thickness. The reverse is true in eyes with unusually thick corneas, he explained. Therefore, without corneal pachymetry, many patients with thin corneas who need treatment will not receive it, while many with thick corneas will receive treatment unnecessarily, he noted. "One should look at optic nerve assessment and corneal pachymetry very carefully in all *ocular hypertensives*, particularly in the initial examination," Dr Wilson said. " But where is the evidence that that fact makes any clinical significance or importance in healthy, non OHTN patients is what I am asking you? >Maybe the ohts study and your experts didn't either. These people aren't "my experts". These are just doctors considered widely to be experts in the field of glaucoma. >So be it. You are all wrong. :) >It is not exactly rocket science to place the above patient in the oh >category by definition. Yes it is. "Ocular hypertension" was something that existed before the OHTS. "Arbitrarily" defined to be IOP >21mm Hg (usually) without any evidence of glaucomatous optic neuropathy or the functional consequences of such (i.e., visual field loss). Arbitrarily meaning it was set at 2 standard deviations (SDs) above the average IOP reading. There was no "magic" about 21 except that was what 2 SDs above the average UNCORRECTED Goldmann IOP measurement was. And the "gold standard" for measuring IOP was, and still is considered to be, Goldmann tonometry. So, classifying someone as OHTN or not prior to the OHTS was always based on a comparison point using uncorrected Goldmann tonometry readings. The OHTS study didn't tell us we should come up with a new definition of OHTN, and there is no evidence we should change the definition of OHTN based on the OHTS. (Unless again you were compensating for CCT like 20 years ago when no one else was?) >Sorry, I attended Berkeley. So did Barry Weissman, and I forgave him. >I always challenge authority. Maybe you will be the next Nicolaus Copernicus? My impetus here is not to shoot you down. It's to really make you think that maybe you *really* need to re-think things if the OHTS and pretty much every glaucoma expert I have talked to disagrees with you. I must admit, I initially thought what you wrote made some sense. That is until I communicated with several glaucoma experts, listened what they consistently claimed was the error in your reasoning, and re-read the OHTS. >And I do believe that although pachymetry is not required by all >"authorities" at this time, it soon will be. Berkeley grads typically dig research while SCCO grads are into patient care, right? :) Why not come up with a study -- gotta be double-blind. Something like this (I'm probably way off on the protocol, but the idea is there): Take a bazillion patients. Check their Goldmann IOPs and measure their CCTs. Determine which of these progress to develop glaucoma and which do not. Give all that data to the statisticians. Discover if adjusting Goldmann IOPs based on a patient's CCT in non OHTN patients is important in real life rather than theoretically important. |
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