Imaging shear stress distribution and evaluating the stress concentration factor of the human eye.

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

Multidisciplinary Ophthalmic Imaging Henle Fiber Layer Phase Retardation Changes Associated With Age-Related Macular Degeneration

PURPOSE. To quantify and compare phase retardation amplitude and regularity associated with the Henle fiber layer (HFL) between nonexudative AMD patients and age-matched controls using scanning laser polarimetry (SLP) imaging. METHODS. A scanning laser polarimeter was used to collect 15 3 158 macular-centered images in 25 patients with nonexudative AMD and 25 age-matched controls. Raw image data were used to compute macular phase retardation maps associated with the HFL. Consecutive, annular regions of interest from 0.5 to 3.08 eccentricity, centered on the fovea, were used to generate intensity profiles from phase retardation data and analyzed with two complementary techniques: a normalized second harmonic frequency (2f) of the fast Fourier Transform (FFT) analysis and a curve fitting analysis using a 2f sine function. Paired t-tests were used to compare the normalized 2f FFT magnitude at each eccentricity between the two groups, the eccentricity that yielded the maximum normalized 2f FFT between paired individuals across the two groups, and curve fitting RMS error at each eccentricity between the two groups. RESULTS. Normalized 2f FFT components were lower in the AMD group at each eccentricity, with no difference between the two groups in the maximum normalized 2f FFT component eccentricity. The root-mean-square (RMS) error from curve fitting was significantly higher in the AMD group. CONCLUSIONS. Phase retardation changes in the central macula indicate loss and/or structural alterations to central cone photoreceptors in nonexudative AMD patients. Scanning laser polarimetry imaging is a noninvasive method for quantifying cone photoreceptor changes associated with central macular disease