Ex Vivo Measurement of Postmortem Tissue Changes in the Crystalline Lens by Brillouin Spectroscopy and Confocal Reflectance Microscopy

Abstract

Use of Brillouin spectroscopy in ophthalmology enables noninvasive, spatially resolved determination of the rheological properties of crystalline lens tissue. Furthermore, the Brillouin shift correlates with the protein concentration inside the lens. In vitro measurements on extracted porcine lenses demonstrate that results obtained with Brillouin spectroscopy depend strongly on time after death. The intensity of the Brillouin signal decreases significantly as early as 5 h postmortem. Moreover, the fluctuation of the Brillouin frequency shift inside the lens increases with postmortem time. Images of lens tissue taken with a confocal reflectance microscope between measurements reveal a degenerative aging process. These tissue changes correlate with our results from Brillouin spectroscopy. It is concluded that only in vivo measurements appropriately reflect the rheological properties of the eye lens and its protein concentration.

In Vivo Brillouin Analysis of the Aging Crystalline Lens

“…This result was confirmed by the ex vivo experiments, where we compared Brillouin moduli to shear moduli measured by traditional gold-standard shear rheometry. Our result is consistent with findings based on previous Brillouin scattering experiments, 21 , 24 , 29 , 44 , 45 bubble-based acoustic radiation force, 19 , 46 and conical probe indentation, 18 in which the elastic modulus in the nucleus was always larger than in the cortex in both animals and human samples. However, these results do not agree with other experiments using spinning platforms and localized small probes in which the nucleus was found to be softer than the cortex in human lenses at ages up to 30 to 50 years old.…”

“… 18 , 19 Ex vivo rheological assessment is also compounded by postmortem changes of the structural and mechanical properties of the lens tissue. 20 , 21 …”

Optical coherence elastography of cold cataract in porcine lens

“…This observation can be associated with residual effects of cataract formation, or overall changes in lens elasticity after 6 h of storage, for example, the loss of crystalline proteins after storage. 54 Previous work has shown that the duration of heating can also increase the elasticity of the lens. 50 When human lenses were heated for 4 h, the shear modulus was .…”

Inverse elastographic method for analyzing the ocular lens compression test

“…6). Since the reported value of for the porcine lens is 2.5-3.0 GPa, 46 the optimal value of G is e®ectively independent of as long as the /G ratio exceeds 100. This approach was previously adopted by Burd et al, who¯xed the ratio of bulk modulus to shear modulus at 100 for all simulations.…”