Frequently Asked Questions

Measurement Parameters

What is Hysteresis?

What is the difference between viscous and elastic resistance?

Elastic materials are those for which strain
(deformation) is directly proportional to stress (applied force), independent of the length of time or the rate at which the force is applied.

Viscous materials are those for which the relationship between strain and stress depends on time or rate. The resistance to the applied force depends primarily on the speed at which the force is applied (greater speed = greater
resistance).

Structures or systems that are said to be “visco-elastic” contain characteristics of both types of material. A simple example is an automotive suspension strut assembly.

There is a component of static resistance (a coil spring) and a component of dynamic resistance (a shock absorber, also known as a damper). Together, the two parts make up a visco-elastic system. The response of such a system to an applied load depends upon the material properties, the magnitude of the force, and the rate at which the force is applied.

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)?

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?