What is the role of the Ocular Response Analyzer (ORA) in the workup of primary open-angle glaucoma (POAG)?

Updated: Mar 14, 2019
  • Author: Kristin Schmid Biggerstaff, MD; Chief Editor: Inci Irak Dersu, MD, MPH  more...
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Answer

Other technologies for measuring intraocular pressure continue to be studied to determine if they are more accurate than Goldmann tonometry. To date, none have been able to surpass it in accuracy for all patients; however, in the future, they may be useful for those who have abnormal pachymetry or other corneal properties. Their role is yet to be finalized. [15, 16, 17, 18] Two examples of new technology are described below.

The Ocular Response Analyzer (ORA)® from Reichert [19] uses a rapid air impulse and an electro-optical system to record two applanation pressure measurements; one measurement is while the cornea is moving inward, and the other measurement is as the cornea returns. Because of its biomechanical properties, the cornea resists the dynamic air puff, thereby causing delays in the inward and outward applanation events and resulting in two different pressure values. See the image below.

Intraocular pressure measurements. Adapted from Re Intraocular pressure measurements. Adapted from Reichert Ophthalmic Instruments, Ocular Response Analyzer, How does it work Web page.

The average of these two pressure values provides a repeatable, Goldmann-correlated IOP measurement. The difference between these two values is referred to as corneal hysteresis, which is a measurement of the corneal tissue properties that is a result of viscous damping in the corneal tissue. Low corneal hysteresis demonstrates that the cornea is less capable of absorbing (damping) the energy of the air pulse. There is good evidence that glaucoma progresses at a faster rate in patients who have low corneal hysteresis.

Some experts hypothesize that this is not primarily a function of corneal thinning, but rather a result of weakening of the tissue structure related to creation of the flap. Decreased corneal hysteresis may also play a role in indicating the presence or onset of other corneal tissue disorders.


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