Pachymeters help you achieve accurate corneal thickness measurements in your patients; however, if one is wearing contact lenses or has ocular disorders the readings could be drastically affected. Today, there are a few things that should be considered when you are ready to take measurements or make your next pachymeter purchase.
When To Measure
There is no best time of day to perform pachymetry, says Dr. Elliot M. Kirstein, OD, FAAO, director of Harper’s Point Eye Associates in Cincinnati
However if a patient has contact lenses, Dr. Kirstein says “The eye should be measured after a lens is removed - then an hour or two later after the cornea recovers to the original thickness.”
Today's Five Biggest Pachymeter Considerations
1) Today's ultrasound pachymetry is popular due to its low cost, simple usage and its ease of repeatable use. Elliot M. Kirstein, OD, FAAO, director of Harper’s Point Eye Associates in Cincinnati, believes ultrasound represents at least 98% of today's pachymetry market.
2) Traditional optical slit-lamp pachymetry is an aging technology that few use anymore.
According to J. James Thimons, OD, Medical Director for Ophthalmic Consultants of Connecticut; pachymeters like the scanning-slit devices are using optical principles to discover relative changes in corneal thicknesses. These kinds of pachymeters are not equally accurate to other technology approaches.
Within the variations on this technology, optical pachymeters “tend to read thinner in my experience,” Dr. Thimons said.
Some factors can cause a cornea to be thicker or thinner than average, according to Dr. Kirstein, research coordinator at Ziemer Ophthalmology.
3) These ultrasonic probes will provide highly accurate density analysis of this tissue. They analyze front and back so that surface reflection properties are measured accurately. Ultrasonic pachymeters are the most accurate of those now available.
4) A nomogram can compensate for the discrepancy of optical pachymeters that read a bit thinner.
Most doctors prefer the ultrasound systems. This is due to correlation with important Ocular Hypertension Treatment Studies - a set baseline for all basic decisions about treatment of glaucoma patients.
5) About The New Pachymeter Options
Murray Fingeret, OD, chief of optometry at the Department of Veterans Administration New York Harbor Healthcare System in Brooklyn, acknowledged that newer pachymeters take multiple measurements at one time. “As long as the standard deviation is relatively low – preferably under 5 microns – these measurements are accurate,” Fingeret said.
New imaging devices that utilize Scheimpflug cameras - are also showing reliable corneal thicknesses from one limbus to the other, however they are not competitive with ultrasound price point.
Citation: information for parts of this article were excerpted from Primary Care Optometry News, October 2007 in an article by Bob Kronemyer.