“As important as the Ocular Hypertension Treatment Study is in total, one of the most significant points raised was the relationship between the central corneal thickness measurement and intraocular pressure,” proclaims Martin Wand, MD, a glaucoma specialist in Hartford, Conn. “Anybody who reads the literature is aware of that. But prior to OHTS only a few of us really knew what to do with this information in practice.” In this article, ophthalmologists focused on glaucoma explain why embracing the routine measurement of pachymetry is worthwhile. Also reviewed are a number of smaller, user-friendly pachymeters designed to make measurement easy, accurate and fast.

The Message
“It’s clear to me that more than any other finding by recent clinical trial, clinicians have embraced and adopted the procedure of measuring central corneal thickness,” states Robert D. Fechtner, MD, of the University of Medicine and Dentistry of New Jersey in Newark. “The OHTS called our attention to CCT as a potential independent risk factor for developing glaucoma, and I believe this news has been widely disseminated.”

Dr. Wand is not quite as confident that the message has gotten through about the role of pachymetry in glaucoma management. “Given what OHTS has taught us, you cannot properly evaluate a glaucoma patient without doing the pachymetry. But I don’t think that this point has filtered down adequately to the general ophthalmologist for a couple of reasons. The main one being just the cost of getting a pachymeter. While we do now have Level I coding for this exam, the payment comes out to only about $11—for both eyes.”

Accutome’s AccuPach V has a voice option that speaks results aloud.

He continues: “When you consider the investment in a $4,000 machine that might only be used on a few of the 30 patients a general ophthalmologist sees everyday, I can understand how he might decide against it.”

While a strong advocate for measurement of CCT, Dr. Wand firmly states that pachymetry does not need to be done on every patient who is seen for every complaint. “However, in any patient who is either a glaucoma suspect, has low-tension glaucoma, ocular hypertension, and I daresay virtually any patient who is already on treatment, it’s a critical one-time measurement,” he says. For this reason, Dr. Wand is disappointed in insurance companies that reimburse only for pachymetry on OAG suspects, saying that ruling “defeats the purpose, the benefit, of this particular test.”

A CPT Code and Practice Guidelines
Ronald Fellman, MD, of Glaucoma Associates in Dallas, sits on the Health Policy Committee of the American Academy of Ophthalmology. He considers the work of the HPC to be important because the passage of CPT codes has a profound effect on health care. “Once a code is established, it implies that rigorous peer review has been conducted, and has both scientific and socioeconomic impact.”

“Clearly a mainstream code was needed for pachymetry. The previous code used was a Level III technology assessment code, 0025T,” he explains. “Based on the OHTS data, the HPC now had the evidence to establish a new Level I CPT code for pachymetry. It was clear to the committee that this service should not be bundled with the eye or E/M codes because it was a distinct new service that impacted care in a new way.”

Now that they can be more confident of being paid for this service, some ophthalmologists think the practice of doing pachymetry will spread. New Jersey’s Dr. Fechtner disagrees that pachymetry was sparse to begin with, put off because of a lack of a code. Even now, he believes that ophthalmologists will order pachymetry as a service to their patients, not for what he calls the “remarkably low” reimbursement for the procedure.

Early Revision to Include CCT

The early revision of the AAO’s Preferred Practice Pattern for Primary Open-angle Glaucoma Suspect includes the following language on page 9: “Determination of central corneal thickness: Central corneal thickness is determined in each eye, preferably with an electronic pachymeter. Evaluation of corneal thickness aids in determining risk of developing glaucoma and interpreting unexpected IOP measurement results. Increased corneal thickness can produce falsely high IOP readings, and decreased corneal thickness can produce falsely low IOP readings.”

Another significant development demonstrating the weight ophthalmology is giving to the measurement of CCT is the ahead-of-schedule revision of the Academy’s Preferred Practice Pattern for Primary Open Angle Glaucoma and for OAG Suspect. Dr. Wand, who served as counselor of the American Glaucoma Society to the AAO, says that the AGS worked closely with the AAO to get these early revisions. “If it’s in the PPP, it’s the gold standard of treatment and that’s what needs to be done.” Dr. Wand explains that the new PPPs for OAG and OAG Suspect were not due to be published until February 2005. However, the new PPPs were released in January 2003, two years ahead of schedule and only seven months after the publication of OHTS. “It’s very unusual for an early revision to be published ‘out of cycle,’ ” says Dr. Wand. “But they [the AAO and the AGS] thought the inclusion of CCT measurement was so important that the PPPs for OAG and OAG Suspect were completed ahead of schedule.”

A Correction Factor
Dr. Fechtner is quick to point out that OHTS tells us a lot more about glaucoma management than just the need to convert the measured IOP. “It was only once the OHTS came out that CCT was suggested to be an independent risk factor for glaucoma,” he says. “By that I mean it might be not just the effect that CT has on the measurement of pressure, but at least in one study, the effect appears to be independent of the influence it has on the pressure measurement.”

Dr. Fellman agrees that at this point we don’t need an exact number for the adjusted IOP: “We just need doctors to realize that the current pressure they check in the office may not be perfect.” He says that simply noting that the cornea is normal, thick or thin is useful. “If a patient is worsening at a supposedly acceptable IOP, and the doctor finds the cornea to be thin, it could explain why the patient is worsening,” he reasons. “The doctor has to adjust the IOP down to compensate for this, whether he knows an exact number or not.”

Five IOP conversion formulas are built into the IOPac.

Dr. Fechtner suspects that now with so much interest in the subject, there will be more study on correction factors. “We might learn it is not only the central cornea that affects the pressure reading; we may need to sample various areas in the cornea to understand its architecture,” he says. “Also, the formulas currently out there are linear, and I suspect this may turn out to be a non-linear function.”

Available Units
Device manufacturers have caught on that measuring central corneal thickness has gone mainstream, and have come up with a selection of new pachymeters that, they say, make the routine practice of pachymetry easy, convenient and accurate.

A full-size printer, the ability to average results, battery-powered and portability are the top requests in pachymeters that sales representatives at Accutome hear, says Andrew Chandler, marketing manager for the Malvern, Pa.-based company. “Most machines on the market are pretty accurate now,” he says, “even the handhelds. Much of the accuracy depends on the technique used to take the reading.” Accutome is introducing its AccuPach V in June, which will have an optional, full-size paper printer and can take a number of separate or continuous measurements and offer an average. This pachymeter also has a voice option that speaks results aloud, a feature Mr. Chandler said is appreciated by refractive surgeons who use the pachymeter during surgery.

The AccuPach V includes a conversion factor that can be invoked by the user.
Five IOP conversion formulas are built into the IOPac available from Heidelberg Engineering (Vista, Calif). Timothy Ehrecke, president of Portable Ophthalmic Devices, Inc. (Bettendorf, Iowa), which manufactures the IOPac, adds that there is memory available in the unit for the doctor to add up to three of his own conversion formulas, and users will be able to download any new formulas that emerge via the Heidelberg web site. The IOPac uses Palm technology, a platform with which many physicians are already familiar, says Mr. Ehrecke. He continues that the wireless transmission of information to other hardware, such as a printer, is one feature of their pachymeter that sets the IOPac apart.

DGH Technology (Exton, Pa.) offers the only one-handed pachymeter according to marketing representative Tom McSunas. He believes that convenience is top priority for his customers, and offers them the Pachmate DGH 55. It has only a few buttons but can do bilateral measurements, run an average, and has an IOP conversion formula built into the unit. “And it’s small enough to fit into a lab coat or shirt pocket,” he adds.

Sonogage (Cleveland, Ohio), does include a conversion formula in its pachymeter models because “our customers asked us to include it,” says company president, Alex Dybbs. “While we don’t know the exact number, it helps as a guide,” he explains. The CorneoGage Plus has a white tip on its probe, which Mr. Dybbs says helps the technician visualize better positioning and consequently, get a more accurate reading. To help with technique, the CorneoGage Plus guides the positioning of the probe by restricting the user to being within 5 degrees from perpendicular. Any more, and the machine won’t take a reading.

Pachymeter Manufacturers

A partial listing of companies:

Accutome: accutome.com

DGH: pachymeter.com

Heidelberg Engineering: HeidelbergEngineering.com

Quantel Medical: quantelmedical.com

Sonogage: sonogage.com

Sonomed: sonomed.com

“The usefulness of a handheld or portable pachymeter would vary depending on the office layout. For instance, do they take the unit around to each patient, or is it set up in a certain room?” wonders Dr. Fellman. His office uses a portable Quantel unit and is pleased with its reproducible readings. “Obviously, a reliable reading is still dependent on the skill of the technician, so adequate training is important,” he points out.

“I understand where the equipment manufacturers are coming from in wanting to include a conversion factor in the pachymeter, because most of us want something in black and white, an exact figure,” acknowledges Dr. Wand. “Unfortunately, it doesn’t work that way. Nothing but sticking a needle into the eye is going to give us the true pressure.”

“We need to keep in mind that the treatment of glaucoma is not based on any number or any single test,” he summarizes. “It’s really the combination of everything—the whole examination of the patient, the family history, the lifestyle, the progression in the past. That’s the art of medicine; to be able to put all of these bits of information together and arrive at what’s best for the individual. We can’t rely on pachymetry to solve our problem, but it has made us aware that the pressure reading is not nearly as accurate as we thought.” 

Review published a table of widely used correction values in its July 2002 article, “Rethinking Pachymetry and Intraocular Pressure,” by Leon Herndon, MD. Visit http://www.revophth.com/index.asp?page=1_144.htm.