IOP: Corneal hysteresis

Corneal hysteresis (CH) is a measurement that reflects the viscoelastic properties of the cornea and its biomechanical integrity. Hysteresis is expressed in units of mmHg, just like intraocular pressure (IOP). Unlike IOP, CH shows no significant variation throughout the day [1]. The Ocular Response Analyzer (ORA) (Reichert Corp. Buffalo, NY) is an instrument that measures CH. It uses a rapid air pulse to record two applanation pressures (Fig. 11.1) [2]. One applanation pressure is recorded while the cornea is moving inward, during indentation, and the second is measured while the cornea is moving outward (while recovering from indentation). The difference between the two pressures is CH. These two pressures are different because of corneal resistance properties delaying the inward and outward applanation. © 2010 Springer-Verlag Berlin Heidelberg.

Duke Scholars

Author Leon Walker Herndon Jr. Ophthalmology, Glaucoma