The Ocular Response Analyzer (ORA) is the only instrument in the world capable of measuring Corneal Hysteresis (CH); an indication of the biomechanical properties of the cornea. This information is different from thickness or topography, which are geometrical attributes of the cornea. CH represents a tissue property, which provides more comprehensive information about ocular biomechanics. There are over 225 publications about ORA in the peer-reviewed literature
The CH measurement provides independent information that aids in the diagnosis and management of glaucoma. In cornea and refractive surgery, the Ocular Response Analyzer enables physicians to better identify eyes at risk of keratoconus. Finally, corneal biomechanics are what really influence the accuracy of tonometers. ORA's ability to measure biomechanical properties of the cornea enables the device to provide corneal compensated IOP, called IOPcc, which has been proven to be less influenced by corneal properties than Goldmann or other methods of tonometry.
Leon Herndon, MD (Associate Professor of Ophthalmology at Duke Eye Center) and James Brandt, MD (Professor of Ophthalmology & Vision Science Director, Glaucoma Service, UC Davis) discuss the measurement of corneal biomechanics with the Ocular Response Analyzer and the clinical implications of these measurements in Glaucoma.
Clinical Applications of the Ocular Response Analyzer:
The Ocular Hypertension Treatment Study (OHTS), and similar studies, have brought to light the relevance of corneal thickness in glaucoma. Numerous studies utilizing the Ocular Response Analyzer have confirmed the importance of the cornea in glaucoma decision making, demonstrating that the CH measurement is of even greater significance than CCT. Studies have proven that low CH is independently associated with glaucoma progression. As such, the CH measurement gives clinicians a new tool to help identify risk of glaucoma progression and to determine which patients may need to be treated more aggressively. The CH measurement has also been shown to be predictive of IOP response to medical therapy, making the CH measurement valuable in setting treatment goals and expectations.
Intraocular Pressure (IOP)
It is widely accepted that the measurement errors in Goldmann tonometry are due to the influence of corneal properties. However it has been determined that mathematical correction of IOP, by means of CCT adjustment algorithms, is invalid and this approach is not useful in individual patients. Quite simply, the thickness of the cornea is not a surrogate for its mechanical bending characteristics.
Ocular Response Analyzer's Corneal-Compensated Intraocular Pressure (IOPcc) takes biomechanical properties into consideration. IOPcc has been shown to be less dependent on corneal properties than other methods of tonometry and more associated with glaucoma status. The instrument?s unique ability to simultaneously provide a Goldmann-correlated IOP measurement (IOPG) and IOPcc provides clinicians with a better understanding of patient tonometry values.
The Ocular Response Analyzer enables clinicians to assess the cornea based on biomechanical tissue properties, rather than geometry only. It has been demonstrated that Corneal Hysteresis (CH) and Corneal Resistance Factor (CRF) measurements are significantly lower in keratoconus patients. Furthermore, CH and CRF are significantly reduced following refractive surgery as a result of complex biomechanical changes. CH and CRF provide a more complete characterization of corneal properties than CCT and topography alone, making these metrics useful in the pre-operative assessment of refractive surgery candidates.
Steven Vold, MD (BoozmanHof Regional Eye Clinic) discusses the clinical implications of corneal biomechanical measurements and the Ocular Response Analyzer with Nathan Radcliffe, MD (Weill Cornell Medical College, New York-Presbyterian Hospital) and David Taylor (Reichert Technologies).
What is Corneal Hysteresis?
Corneal Hysteresis (CH) is the difference in the inward and outward pressure values obtained during the dynamic bi-directional applanation process employed by the Ocular Response Analyzer, as a result of viscous damping in the cornea. It is a characterization of the cornea?s energy absorption capacity, which is a function of the biomechanical properties of the cornea.
Ocular Response Analyzer is the only instrument in the world capable of measuring corneal biomechanical properties and Corneal Compensated IOP.
How it Works.
The Ocular Response Analyzer utilizes a dynamic bi-directional applanation process to measure biomechanical properties of the cornea and the intraocular pressure of the eye. A precisely metered collimated air-pulse causes the cornea to move inwards, past applanation, and into a slight concavity. Milliseconds after applanation, as the air pulse force decreases, the cornea begins to return to its normal configuration. In the process, it once again passes through an applanated state.
An electro-optical system monitors the curvature of the cornea throughout the deformation process taking 400 data samples during the 20-millisecond measurement. Two independent pressure values are derived from the inward and outward applanation events. Viscous damping in the cornea results in an offset between the inward and outward pressure values. The difference between these two pressure values is Corneal Hysteresis (CH).
Comprehensive Pressure and Cornea Information
Powerful Software Package
Ocular Response Analyzer: At a Glance
Catalog Number -
16070 Ocular Response Analyzer System
16071 Ocular Response Analyzer System with chinrest
Measurement Range: 0 - 60 mmHg
Display Resolution: +/- 0.10 mmHg
Note: The accuracy complies with ISO 8612 Tonometer Standard
Voltage: 100 - 240 volts AC 50/60 Hz
Current: 1.5 A
Watts: 40 - 75 VA
Fuses: Slo-Blo(T), 2.5 Amp, 250V, glass type, 5x20mm
Operating System -
Windows 7® 32-bit, Embedded
Physical Dimensions -
Height: 17.0 inches (43.2 cm)
Width: 9.5 inches (24.1 cm)
Length: 13.5 inches (34.3 cm)
Weight, unpacked: 30 lbs. (13.6 Kg)
Screen: 12.1 inches
Provides the most clinically relevant measure of IOP.