The entire thrust of the article is related to the accuracy of the Goldmann tonometer, factors that influence the accuracy of the tonometry, tonometers that appear to be more accurate than Goldmann, and the future of tonometry. But the article totally ignored a key issue of importance.
Corneal biomechanics have a major impact on the accuracy of IOP measurement devices. Reichert pioneered the Ocular Response Analyzer (ORA), which has been commercially available since 2005 and in clinical research since 2002. This is the only device in the world capable of measuring corneal biomechanical properties. One of the features of the ORA is a “cornealcompensated” IOP, which reduces the influence of the cornea on the IOP measurement. Dr. Leon Herndon, who was quoted in this article, is a user of the ORA. He mentioned “corneal biomechanics” in his quote at the beginning of the article. It is my assumption that he referred specifically to the ORA in his interview, but there was no mention of this in the article.
ORA put corneal biomechanics on the map. As a result of this device, there are now entire program sections of major meetings (ASCRS, ESCRS, AAO, ARVO, etc.) dedicated to the topic of corneal biomechanics. There are more than 175 published articles about ORA and corneal biomechanics in the peer-reviewed literature. Dozens of these papers by high-profile opinion-leading ophthalmologists demonstrate that our IOP measurement is less affected by corneal properties and a better indicator of glaucomatous VF loss and progression than Goldmann. In the World Glaucoma Association’s book Intraocular Pressure Consensus Series 4, the ORA is specifically referenced as a tonometer that is less affected by corneal biomechanics than Goldmann.
In the segment of the article related to “Other Technologies” (p. 47), there is again no mention of ORA.In the first paragraph of this section the author erroneously claims that rebound tonometry is not as likely to be affected by corneal properties. This is totally inaccurate and there are numerous publications in the literature that demonstrate rebound tonometry is MORE affected by corneal properties than Goldmann.
I believe the omission of a discussion of the ORA has done a great disservice to your readers by not including a very important issue that is central to the focus of the article.
Advanced Diagnostic Devices
To the Editor:
My comments are in response to your June 2011 issue of Review. Though interest in diurnal IOP seems to wax and wane, it appears that, once again, the heat is up. The proverbial questions are: Can better knowledge of individual fluctuations heighten our ability to prognosticate glaucomatous progression? And, if so, how shall we acquire this knowledge?
I wear two hats on this issue. First, I am a doctor, spending the majority of my working hours diagnosing and managing glaucoma. Wow, wouldn’t it be great to have a practical, approvable technique for acquiring diurnal IOP data? It would be even better if I could get paid a little for doing the test.
Here’s where my ophthalmic industry hat goes on. The real question is not “Do we have the technology?” We do. The problem is that industry cannot figure out how to bring us a test that is sanitary, affordable and practical. While we can be reimbursed for properly administering diurnal IOP measurement, insurance law prohibits physicians from passing the costs of testing consumables or additional hardware on to the patient. So, if the ideal IOP contact lens is invented, what should the cost to the end user (doctor) be? Can industry produce a reliable disposable devise for under $25? How can we reliably prevent cross contamination with a reusable device, or can we make a cheap disposable device?
It is unfortunate that, in the immediate future, diurnal devices will probably only be practical in research or institutional settings. If there is someone out there who can deliver a more optimistic picture, please do so. My patients are waiting.
My second comment is in response to Dr. Lehrer’s reported observation that Pascal tonometric values tend to drift downward as the instrument ages. Let me begin by saying that the Pascal is a precision electronic device. Like all electronic and mechanical devices (including Goldmann tonometers) it can be broken. Fortuitously, the error that Dr. Lehrer reports can easily be prevented.
First is the matter of technique. If a patient receives the test for the first time, we can expect him to be anxious. First readings are often high. Keep in mind that, while the Pascal is precise, it cannot know if the patient is holding his breath or squeezing his lids. That’s the doctor’s job. There is extensive information on the topic of variability of IOP included in this same issue of Review.
The Pascal comes with instructions as well as access to support personnel within the company to help physicans understand the instrument and manage questions. The simple way to check Pascal tip performance is the Pascal “Q” value. If one cannot achieve values of one or two on a typical patient, there may be a problem and you should call Ziemer technical support ASAP. If you call Ziemer, they can easily show you how to check for a broken sensor or check it for you. By the way, they’ll probably direct your call to me!
Elliot Kirstein, OD
Director at Harper's Point Eye Associates
former director at Ziemer Ophthalmology