When discussing controversial treatments and new clinical protocols, point/counterpoint presentations remain an excellent method for providing readers with reasonable element of balance. Dr. Andrew S. Gurwood contributed to the Optometric Study Center, High-Tech Glaucoma Devices Hasten Diagnosis (July 15, 2004), with his robust support of keeping Goldmann applanation tonometry as the gold standard in measuring IOP in the context of a newer, perhaps more dependable, technology. Its just too easy to respond to his flawed arguments.
First, Dr. Gurwood states that the Ocular Hypertension Treatment Study (OHTS) revealed a linear relationship between central corneal thickness (CCT) and IOP. His point is, at best, unclear and misleading. To clarify, OHTS found that thin corneas appear to represent an independent risk factor for glaucoma.
Second, he emphasizes the multi-variant etiology of glaucoma and states that too much value should not be given to only one screening test such as IOP. I handily agree. In my practices two offices, excellent history taking, threshold fields, gonioscopy, diurnal IOP, nerve imaging, blood flow analysis and pachymetry support our glaucoma management decisions.
There is no silver bullet in glaucoma diagnosis. We simply want to use the most accurate instrument to measure each parameter.
Medical tests such as Goldmann, which render false negatives, are dangerous. It means that too many sick people will be overlooked.
As Dr. Gurwood stated, Goldmann recognized the limitations of tonometry, but understood that, as a screening tool, it could alert practitioners to the potential risk of disease. Why not use a device that does the screening in a more error-free fashion?
Goldmann is clearly misleading with thin, thick and/or edematous corneas, as well as post-op LASIK, keratoconus and other patients. These patients represent a significant percentage of everyday optometric patient populations.
A tonometer that is unaffected by LASIK is unquestionably worthy of a close look by the eye care community.Elliot M. Kirstein, O.D., www.drkirstein.com
Editors note: Dr. Kirstein is a consultant for Ziemer Ophthalmic Systems AG, the company that manufactures the Pascal dynamic contour tonometer.
Dr. Gurwood responds:
I thank Dr. Kirstein for pointing out the significant error, that slipped by the proofreading of my article, Another Perspective: Goldmann is Still the Gold Standard. The statement, the OHTS study revealed a linear relationship between CCT and IOP, is incorrect. The statement should have read, the OHTS study revealed a non-linear relationship between CCT and IOP. I apologize for this error.
Further, I appreciate Dr. Kirsteins passion for this new technology and the authentic enthusiasm he has for its inclusion in the diagnostic armamentarium for glaucoma.
It would be unwise to adopt a position against new technology capable of enhancing diagnostic yields. The Pascal tonometer does not meet these criteria. The Pascal is unwarranted and cost-ineffective when you consider that:
IOP is but a relative risk factor in the diagnosis of glaucoma.
Published algorithms accurately approximate the IOP corrected for CCT when such a conversion is necessary.
OHTS showed that CCT and IOP have a non-linear relationship, making CCT a risk a factor in-and-of-itself, independent of IOP, and making it necessary to obtain that data since we can interpret the constellation of signs and symptoms of glaucoma independently of knowing the corrected or true IOP.
All IOP measurements in the same office are relative to each other.
I do not contest the Pascals capability or that its data are accurate. My contention points out that the current system of Goldmann (with conversion as needed), in concert with all the other data, results in the same yield.
The Pascal tonometer is a luxury car. Its expensive and will require additional specialized maintenance or procedures to prepare it, you will have to go back to the old method if it breaks down, and its value (for now) is a matter of opinion, with no evidence to indicate that its use is beneficial in reducing false positives, false negatives or altering management regimens. Im sure that, if they were free, everyone would like to have one, but does it really get you where you want to go any better than what you had before?
-Andrew S. Gurwood, O.D.