In Vivo Biomechanical Measurements of the Cornea

Abstract

In early corneal examinations, the relationships between the morphological and biomechanical features of the cornea were unclear. Although consistent links have been demonstrated between the two in certain cases, these are not valid in many diseased states. An accurate assessment of the corneal biomechanical properties is essential for understanding the condition of the cornea. Studies on corneal biomechanics in vivo suggest that clinical problems such as refractive surgery and ectatic corneal disease are closely related to changes in biomechanical parameters. Current techniques are available to assess the mechanical characteristics of the cornea in vivo. Accordingly, various attempts have been expended to obtain the relevant mechanical parameters from different perspectives, using the air-puff method, ultrasound, optical techniques, and finite element analyses. However, a measurement technique that can comprehensively reflect the full mechanical characteristics of the cornea (gold standard) has not yet been developed. We review herein the in vivo measurement techniques used to assess corneal biomechanics, and discuss their advantages and limitations to provide a comprehensive introduction to the current state of technical development to support more accurate clinical decisions.

Keywords: bioengineering; biomechanics; corneal; ophthalmology.

Figure 1

Development of in vivo corneal biomechanical measurements. Initial techniques for assessing the corneal mechanical characteristics utilized air puffs (e.g., ocular response analyzer (ORA)) [14]. Later, less destructive corneal deformation techniques, such as ultrasound (mechanical waves) [16,17], were developed. In recent years, new technologies such as brillouin microscopy (BM) [18] have emerged. Some commercial devices (ORA, corneal visualization Scheimpflug technology (Corvis ST)) are now used in clinical settings.

Figure 2

Example of an ectatic eye observed using Corvis ST and Pentacam. Corneal parameters are displayed in the upper left and corneal deformation morphology is displayed in the lower left. Corneal morphological data are shown on the right. The Belin−Ambrósio display (BAD) D is a parameter based on corneal morphology to assess the risk of corneal ectasia. The corneal biomechanical index (CBI) and the total biomechanical index (TBI) are shown at the bottom.