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Frequently Asked Questions
Measurement Parameters
- What is Hysteresis?
- What is the difference between viscous and elastic resistance?
- How is Corneal Hysteresis measured?
- What is Corneal Hysteresis
- What is IOPg?
- Is IOPg different from the IOP value presented by a traditional Non-Contact Tonometer (NCT)?
- Yes. In a traditional NCT the IOP measurement is made by applanating the cornea using a precisely-metered collimated-air-pulse. As the cornea moves inward under the force of the air-pulse, the shape of the cornea is monitored by an electro-optical applanation detection system. When the cornea reaches applanation, the air-pulse pressure value is recorded and converted to a Goldmann-correlated IOP measurement in mmHg.
The Ocular Response Analyzer works in a similar manner, except that it uses a bi-directional applanation process. Under the force of the air-pulse, the cornea moves inward, past initial applanation, and then returns as the air-pulse pressure declines. The applantion pressure is recorded at both the inward and outward applanation events. These pressure values are avereaged and then converted to mmHg to provide a Goldmann-correlated IOP value. The averaging of the inward and outward applanation events reduces measurement error that may result from "dynamic corneal resistance" in response to the dynamic nature of the air-pulse. The result is a stronger correlation with Goldmann-measured IOP values than with a traditional NCT.
- Is there a massage effect caused by repeated measurements with the Ocular Response Analyzer?
- What is IOPcc?
- How is IOPcc measured?
- What is CRF?
- What is the range of Corneal Hysteresis in normal Subjects?
- What is the range of Corneal Resistance Factor (CRF) in normal subjects
- What is the average value of Corneal Hysteresis in normal subjects?
- What is the average value of Corneal Resistance factor (CRF) in normal subjects?
- Are CH and CRF Related to the “Modulus of Elasticity” of the cornea?
- What is the acceptable repeat measurement variability for the corneal hysteresis measurement?
- What is the acceptable repeat measurement variability for the corneal resistance factor (CRF) measurement?
- Why is IOPg higher/lower than my Goldmann IOP value?
- How do Corneal Hysteresis (CH) and Corneal Reistance Factor (CRF) differ?
- Is Corneal Hysteresis (CH) related to Central Corneal Thickness (CCT)?
Interpreting results
- What is the average value of Corneal Hysteresis in normal subjects?
- What is the acceptable repeat measurement variability for the corneal hysteresis measurement?
- What is the acceptable repeat measurement variability for the corneal resistance factor (CRF) measurement?
- Why is IOPg higher/lower than my Goldmann IOP value?
- What are the characteristics of a "good" measurement signal for a normal subject?
- How can I tell a "bad signal" from a "good signal"?
Using the instrument
- What is the acceptable repeat measurement variability for the corneal hysteresis measurement?
- What is the acceptable repeat measurement variability for the corneal resistance factor (CRF) measurement?
- Why is IOPg higher/lower than my Goldmann IOP value?
- Why are the average values in the software different from the true mathematical average?
- Where are the results saved when I use the pachymeter?
- Should I use anesthesia before taking an Ocular Response Analyzer measurement?
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