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 for printing.
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.