Experimental assessment of human corneal hysteresis.
OBJECTIVE
Hysteresis is a viscoelastic property characterized by the difference in behavior under loading and unloading. The aim of the study was to determine corneal hysteresis using experimental means.


METHODS
Twenty-nine human corneas with 50-95 year age were subjected to cycles of pressure loading and unloading. Two pressure application rates were adopted to approximate static and dynamic loading conditions.


RESULTS
The behavior under both loading and unloading was found to stiffen with increased age. The unloading behavior appeared to be largely independent of the pressure level at which unloading started. The difference between the behavior patterns under loading and unloading was quantified and used as a measure of corneal hysteresis. The hysteresis area was significantly larger with faster loading and with decreased age.


CONCLUSIONS
The trend for hysteresis to decrease with age is in agreement with previous clinical observations. Hysteresis was also found to increase with faster pressure application.
Elsheikh
Ahmed
A
Division of Civil Engineering, University of Dundee, Dundee, United Kingdom. a.i.h.elsheikh@dundee.ac.uk
Wang
Defu
D
Rama
Paolo
P
Campanelli
Marino
M
Garway-Heath
David
D
D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D003187:Compliance; D003315:Cornea / Q000502:physiology*; D004547:Elastic Tissue / Q000502:physiology*; D006801:Humans; D008433:Mathematics; D008875:Middle Aged; D008954:Models, Biological; D011312:Pressure; D013314:Stress, Mechanical