Abstract
Healthy eyes are vital for a better quality of human life. Historically, for man-made materials, scientists and engineers use stress concentration factors to characterise the effects of structural non-homogeneities on their mechanical strength. However, such information is scarce for the human eye. Here we present the shear stress distribution profiles of a healthy human cornea surface in vivo using photo-stress analysis tomography, which is a non-intrusive and non-X-ray based method. The corneal birefringent retardation measured here is comparable to that of previous studies. Using this, we derive eye stress concentration factors and the directional alignment of major principal stress on the surface of the cornea. Similar to thermometers being used for monitoring the general health in humans, this report provides a foundation to characterise the shear stress carrying capacity of the cornea, and a potential bench mark for validating theoretical modelling of stresses in the human eye in future.
Highlights
Unlike in the case of man-made materials, information on the shear stress distribution characteristics and estimates of shear stress concentration factors of the human eye is scarcely found in the literature
The study is based on measuring birefringence in the cornea[3] (Fig. 1) using photo stress analysis tomography (PSAT), a method well known in engineering[4] and medical applications[5] for visualising stresses in birefringent materials
The shear stress distribution at both the horizontal and vertical planes, and at the plane carrying maximum shear stress of the cornea is shown to have a good level of correlation with the diamond-like architecture of corneal tissues[16] (Figs. 4, 5)
Summary
For man-made materials, scientists and engineers use stress concentration factors to characterise the effects of structural non-homogeneities on their mechanical strength Such information is scarce for the human eye. We provide in-vivo distribution of shear stress and stress concentration characteristics on the surface of a healthy human eye. Recent developments in the digital imaging and processing of birefringent data provide the opportunity to visualise shear stress distribution whole-field in the eye This is advantageous as the birefringent measures can be quantified for any point of interest on the surface of cornea in relation to its optical axes. Previous studies on birefringent measurements in the human eye have focused mainly on the medical treatment perspectives for example, to characterise retinal structures[14], their age effects[14] and in vitro analysis of keratoconus[15].
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