Characterization of Corneal Indentation Hysteresis

Abstract

Abstract-The aim of this study is to design and develop a noninvasive corneal indentation method to measure the corneal hysteresis behavior under dynamic corneal indentation. Corneal indentation method is adapted for the design and development of a measurement method for the characterization of Corneal Indentation Hysteresis (CIH). Fourteen porcine eyes were tested using the corneal indentation method. The CIH measured in enucleated porcine eyes showed indentation rate and intraocular pressure dependences. The CIH increased with the indentation rate at lower IOP (< 25 mmHg) and the CIH decreased with the indentation rate at higher IOP (> 25 mmHg). The CIH was linear proportional to the IOP within an individual eye. The CIH was positively correlated with the IOP, corneal in-plane tensile stress and corneal tangent modulus (E). A new method based on corneal indentation for the measurement of Corneal Indentation Hysteresis in vivo is developed. To our knowledge, this is the first study to introduce the corneal indentation hysteresis and correlate the corneal indentation hysteresis and the corneal tangent modulus. I. INTRODUCTIONThe corneal biomechanical properties are of great interest due to its clinical potential application, particularly in early detection of keratoconus [1]. It has been also suggested that the corneal biomechanical properties may reflect the biomechanical behavior of the globe and give an indication of the susceptibility of glaucoma developing and progression [2,3]. Ocular Response Analyzer (ORA; Reichert Ophthalmic Instruments, Buffalo, NY, USA) is the first commercially available instrument capable to measure in vivo corneal biomechanical properties. The device uses a rapid jet of air to indent the cornea. The infrared reflectance profile from ORA during the bi-directional applanation process is measured and analyzed to provide two parameters of corneal biomechanics, corneal hysteresis (CH) and corneal response factor (CRF). The CH and CRF provided by ORA are non-standard biomechanical terms that are different from the classical knowledge of corneal biomechanics. The CH may be produced with different combinations of elastic modulus and the viscous damping parameters. The aim of this study is to design and develop a Match W. L. Ko is with the