EVALUATING THE CORNEA’S STRENGTH

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Reichert’s ORA is a corneal biomechanics analyzer and a tonometer.

Reichert’s ORA helps to preserve the vision of glaucoma patients.

At its heart, Reichert’s Ocular Response Analyzer (ORA) is a non-contact tonometer (NCT). And while standard NCTs have improved tremendously over the years, the ORA offers something more distinctive than your standard of measuring intraocular pressure (IOP).

UNDERSTANDING THE SCIENCE
Around 2001, David Luce, PhD, of Reichert, figured out there was additional information hidden in the air-puff’s measurement signal…information about the biomechanical properties of the cornea. Without going into a long scientific discussion, suffice it to say pachymeters measure the thickness of the cornea while topographers and keratometers measure the shape. The ORA, one could say, measures the strength of the cornea. (Read more about measuring the curvature of the cornea here.)

Just like the shock absorber on your car when you hit a bump in the road, the cornea flexes inward and outward under the force of the air jet it absorbs, and dissipates energy from the “blast.” Because it is fluid filled (viscous), the shock absorber dampens the force of the blow, thereby preventing the car from jolting violently. The ORA characterizes this shock-absorber capacity of the cornea in a measurement called corneal hysteresis (CH). This is the world’s only indication of in-vivo ocular biomechanics. I’ve found that patients with reduced CH (technically weaker corneas) have a greater likelihood of developing glaucoma as a glaucoma suspect or having progressive glaucoma in diagnosed patients.

COMMENTS FROM THE DOCS


“I love Reichert’s ORA and use it all the time. CH [corneal hystersis]has opened my eyes and helped me to diagnose many more ‘suspects.’”

—Bob Tyszko, OD,
Our Town Eye Care,
Peterborough, NH

“The ORA has become an invaluable instrument in my practice. While I have not abandoned Goldmann applanation tonometry (GAT), I routinely get ORA measurements on all of my glaucoma patients and consider these to be just as critical as the GAT measurements.”

—Robert Wooldridge, OD,
Eye Foundation of Utah,
Salt Lake City, UT

CORNEAL CLUES
Fast-forward to now where, as one might expect of a corneal measurement, CH can aid in the assessment of keratoconus. This is especially important when evaluating LASIK candidates.

The OHTS study in 2002 demonstrated that central corneal thickness (CCT) was a risk factor for conversion to glaucoma. However, there is no linear relationship between CCT and IOP. OHTS concluded that thinner corneas were at higher risk for glaucoma.

In fact, the investigators of OHTS used a number of different CCTIOP correction formulas and none of them made the adjusted IOP more significant than the thickness of the cornea itself. Since then we have learned that CH is a more powerful indicator of glaucoma risk hands-down. What makes it even more interesting is that CH is independently predictive of visual field progression.

A TONOMETER AT HEART

For that reason, as well as others, Reichert’s ORA has proven to be a necessary part of my practice. The machine’s IOPcc (corneal compensated IOP) provides an IOP measurement that agrees with Goldmann on average but is more associated with the status of glaucoma than actual Goldmann measurements. It has little correlation with CCT and stays fairly constant after refractive surgery.

This is important information because every day in my practice I often have to decide whether I need to stay the course or get more aggressive in order to preserve the vision of my glaucoma patients. The ORA and CH are important factors in my decision to not treat a patient with ocular hypertension or even sometimes stop treatment on a patient who has already been taking medication.

Ben Gaddie is the owner and director of the Gaddie Eye Centers, a multi-location full-service practice in Louisville, KY.

WHERE TO FIND IT:

Reichert • 716-686-4500 • reichert.com

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