When corneal tonometry is challenging, measuring IOP through the upper eyelid at the limbus may be an alternative.
“There are certain conditions where you cannot achieve a reliable pressure through the cornea,” Emil W. Chynn, MD, FACS, MBA, of Park Avenue Laser Vision in New York, told Ocular Surgery News. Such conditions include eyes with severe scarring, corneal edema, ocular trauma or a keratoprosthesis.
“At my practice, this represents a small percentage of patients, between 5% and 10%,” Chynn said. “And for general ophthalmologists, it might be only 1% to 2% of patients.”
On the other hand, many children cannot tolerate anyone touching their eyes, so in the pediatric population, perhaps 90% of patients would do better with the Diaton pen (BiCOM) than with Goldmann applanation tonometry, Chynn said.
No contact with cornea
According to Chynn, the Diaton pen is a reputable tonometer that accurately measures IOP. Except for air-puff tonometry, other devices that measure IOP, including the gold-standard Goldmann applanation tonometry, involve contact with the cornea.
There are inherent “dangers” in using a device that touches the cornea, Chynn said, citing corneal abrasion and infection.
“The No. 1 reason non-ophthalmologists shy away from tonometry is that they are afraid of causing a corneal abrasion,” he said.
On the other hand, air-puff testing is not as accurate as Goldmann applanation tonometry.
“I suspect that most ophthalmologists would agree that the air-puff is only good as a screening device,” Chynn said.
The Diaton is useful as a screening device for non-ophthalmologists such as general practitioners, internists or emergency department physicians because there is no contact with the cornea, only the upper eyelid. “There is also no risk of infection or abrasion,” Chynn said.
Using the device
To use the Diaton, the patient lies on a chair, perhaps leaning on the back of the chair, and then looks up at their extended thumb at an approximately 45° angle, centering the eye. The clinician gently positions the tonometer at the edge of the eyelid, so the pen is touching the limbus through the lid at the tarsus. The clinician then slightly taps the pen.
“The mechanism is similar to a Schiotz tonometer in that both devices work on a rebound principle,” Chynn said.
The device is about the size of a highlighter and features a small digital readout. The test takes less than a minute for both eyes.
Chynn said that his research measured accuracy of the Diaton within 2.4 mm Hg, which he said is considered acceptable and close to the accuracy of Goldmann tonometry, which is within 1.9 mm Hg.
A busy general ophthalmologist who sees 50 patients a day could benefit from the Diaton, especially those without a certified ophthalmic medical technician, he said.
Furthermore, there are no consumables, such as replacement tips or covers, and no sterilization is required, so the Diaton is less expensive, Chynn said. And because there is no involvement of the cornea, pachymetry is bypassed to adjust for corneal biometrics.
A second-generation easy-to-use model of the Diaton debuted about 3 years ago, Chynn said.
“Unfortunately, though, most ophthalmologists do not even know this device exists,” he said. – by Bob Kronemyer
- For more information:
- Emil W. Chynn, MD, FACS, MBA, can be reached at Park Avenue Laser Vision, 102 E. 25th St., New York, NY 10010; email: firstname.lastname@example.org.
Disclosure: Chynn reports no relevant financial disclosures.