Product Review: Reichert Ocular Response Analyzer

David A. Goldman, M.D.

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Though our ability to properly screen patients and diagnose them with particular disease is excellent, we continue to improve our methodology so that we may recognize these pathologies sooner and better prevent adverse sequelae. By imaging the cornea with topography maps and dual-scheimpflug images, we may extrapolate about its strength, but in reality we can never be certain. Corneal hysteresis appears to give a very good indication of the biomechanical properties of the cornea in an accurate and repeatable manner.

Corneal hysteresis is the ability of the cornea to absorb and dissipate energy. To measure this, a precise amount of air is pulsed onto the cornea. Similar to with Goldmann tonometry, this air causes the cornea to move inward towards a slight concavity. Following the air pulse, the cornea returns to its original configuration. During this process, an advanced optical system measures this change 400 times during 20 milliseconds. A second independent value is then measured and the average of this is presented as the Goldmann correlated IOP value. The difference between these values (peak and trough) is measured as corneal hysteresis.

These measurements have been shown in multiple studies not only to be repeatable, but to be useful in the detection of glaucoma and keratoconus. Wells et al (IOVS 2008) reported that optic nerve compliance was associated with patients with corneal hysteresis in patients with glaucoma. It was felt that greater corneal hysteresis was associated with more bowing of the lamina with IOP elevation. Bochman et al (Graefes Arch Clin Exp Ophthalmol. 2008) reported that corneal hysteresis was lower in glaucomatous eyes with acquired pit of the optic nerve (APON) vs glaucomatous eyes without APON. Furthermore, several studies have now demonstrated low corneal hysteresis to be associated with more progressive glaucoma independent of its relationship with intraocular pressure. In this manner, we may be able to better predict which of our glaucoma suspect patients are going to develop glaucoma as well as which glaucoma patients are more likely to require more aggressive therapy. As FDA approval of corneal crosslinking occurs, we can expect to hear significantly more discussion regarding corneal hysteresis as a method to measure response to crosslinking. Currently there is only one device that measures corneal hysteresis; the Ocular Response Analyzer from Reichert.

Taking up a very small amount of space, the second generation ORA has multiple features that have been updated: A touch-screen interface that can be mounted on the left or right side of the device allows users maximum flexibility in deciding where to place the device. The newer platform is able to auto-align the patient in the x, y, and z axis in a fast and quiet manner to maximize efficiency and reduce patient fatigue. The interface and associated software have also been upgraded to streamline the entire process. All of these changes have made the testing experience more efficient for the physician and more comfortable for the patient.

As we continue to achieve greater visual outcomes with improving technologies, so too must we improve our screening capabilities. Corneal hysteresis gives us another variable to measure in our pre-refractive and glaucoma suspect patients that will allow us not only to better screen patients for potential disease but also follow conditions such as glaucoma with more accurate IOP measurement. The ocular response analyzer is an excellent practice addition to perform such measurements.