A Look at Corneal Pachymeters
BY MARJORIE J. RAH, OD, PHD
Whether you're co-managing
refractive surgery, treating glaucoma or monitoring corneal edema, you may find
yourself in need of a corneal pachymeter. Pachymetry has changed how we manage glaucoma. Likewise, determining eligibility
for refractive surgical procedures depends on accurate corneal thickness measurements.
Medical plans cover pachyme-try when practitioners use it
to determine the treatment plan for a glaucoma suspect or glaucoma patient. It's
billed as bilateral code 76514 and requires interpretation and report. Some plans
may cover it only once per lifetime.
Several pachymeter models are available in a wide range of prices
and portability. I had the opportunity to observe some of the available instruments
at the 2005 American Academy of Optometry meeting. Not surprisingly, the highlighted
feature was IOP correction. In fact, many pachyme-ters now have a function that
automatically calculates the correction.
The Pachmate DGH 55 (DGH Technology, Inc.) is a portable handheld
model. It's only 6.9 inches long, 1.7 inches wide and weighs a mere 3.6 ounces.
A running average and standard deviation in microns are displayed on the screen
and it will accommodate up to 25 measurements bilaterally. It also displays IOP
correction on the screen. The instrument features an adjustable probe angle that
detaches for cleaning. Standard measurement range is 200μm to 1,100μm
and it has a flap option of 95μm to 1,100μm. The company states an accuracy
range of ± 5μm.
Also from DGH Technology is the Pachette 3. It's portable,
but not handheld. It shares the same features and specifications (with the exception
of size) as the Pachmate DGH 55.
The Corneo-Gage Plus (Sonogage, Inc.) is a slightly larger, but
portable, ultrasonic pachymeter that includes a built-in dot matrix printer. The
manufacturer says a 50 MHz transducer provides accuracy of ± 0.4μm and
a measurement range of 25μm to 2,000μm. This instrument doesn't average
individual readings. The printout displays each individual measurement. The instrument
also has a built-in IOP correction nomogram.
For gadget lovers, Heidelberg Engineering offers the IOPac Standard
and IOPac Advanced pachymeters with a platform based on Palm technology. The probe
ultrasound frequency of 20 MHz provides a measurement range of 300μm to 1,000μm.
The manufacturer says the accuracy range is ± 5μm. The probe is adjustable
to either a straight or a 45-degree angled position. Both models automatically average
readings, display individual measurements and are compatible with medical, pharmaceutical
and ICD-9 Palm software. The Advanced model includes automatic CCT corrected IOP
calculations. It also has refractive measurement capability and infrared capability
There is also a slit-lamp mounted pachymeter available from Haag-Streit
which uses optical coherence reflectometry. According to the company, it has the
ability to measure epithelial corneal thickness and has a non-contact measurement
that is accurate to ± 1μm. A thermal printer is provided with the instrument
along with connections to a PC or laptop computer.
Features and Price
The price for pachymeters begins around $1,995 and increases with
additional features. This list is by no means exhaustive of all the available models,
but represents many of the popular instruments currently available.
Dr. Rah is an assistant
professor at the New England College of Optometry where she works primarily in the
Cornea and Contact Lens Service in patient care, teaching and research.
Contact Lens Spectrum, Issue: February 2006