Wellman Center Lecture Series

Tuesday, April 10, 2018
12:00 – 1:00 pm

"Basic and Clinical Aspects of Corneal and Ocular Biomechanics"

Cynthia J. Roberts, PhD
Professor, Biomedical Engineering
Professor, Ophthalmology
Professor, Surgery OSU Eye and Ear Institute

Abstract:
Knowledge of corneal biomechanical properties is important in understanding the development and progression in many disease processes, as well as in screening for pathologic conditions and monitoring response to treatment. The cornea is a biomechanical structure composed of hundreds of lamellar layers that are oriented in different directions, and provide the strength necessary to contain the intraocular pressure (IOP). Biomechanical properties are a means to quantify the response to an applied load, which is the IOP in the case of the eye. However, measuring classic properties such as modulus of elasticity is challenging in the living eye, where destructive testing is not appropriate. Many technologies are under development, but are years away from translation to the clinic. In addition, the cornea is a viscoelastic material, which means not only that the response is distinct during the loading phase and the unloading phase of the externally applied load, but also that the response has a time-dependent component. In other words, the response will be different as a function of how quickly the load is applied. Two clinical devices are available commercially, and both use an air puff as the applied load on the cornea. The Ocular Response Analyzer (ORA) uses an indirect assessment of deformation response and produces a measurement representative of the viscoelastic nature of the cornea, called corneal hysteresis (CH), as well as pressure and deformation signals that can be analyzed for the cornea elastic response. The air puff is a function of how quickly the cornea applanates, with lower air pressure for a faster applanation or lower IOP. The Corvis ST uses a high speed camera with Scheimpflug geometry, to allow direct assessment of deformation response to a consistent air puff. Dynamic corneal response parameters are extracted from a series of images captured during the exam. However, for both devices, the strongest predictor of deformation amplitude is IOP, which must be taken into account in order to assess corneal biomechanics. Clinical applications and interpretation of the data produced by these devices will be discussed, including refractive surgery, keratoconus, corneal collagen crosslinking, and IOP measurement error.