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B. I. Gaynes, M. Anastasio, E. Brey, C.-Y. Chou; Phase Contrast Imaging of the Mammalian Lens. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2019. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Phase contrast diffraction enhanced imaging (DEI) employs low dose spatially coherent energy to exploit changes in the refractive index of a specimen in order to provide scatter free images of both refractive and absorptive character. In addition, phase contrast images are amenable to tomographic reconstruction providing unique 3-dimensional visualization of a specimen. Since lens structure and function is uniquely based on a gradient of refractive indices, DEI is a particularly appealing methodology to apply to lens imaging. This study provides illustrative ex-vivo images obtained with phase contrast DEI in regard to the mammalian lens.
Adult New Zealand white rabbit lenses were subjected to two dimensional, diffraction enhanced phase contrast imaging. Eyes were enucleated and the lens removed and fixed in 2.5% glutaraldehyde in 0.07 m sodium cacodylate buffer at pH 7.2 for 24 hours. Following fixation, the lenses where placed in a custom designed specimen holder perpendicular to the imaging beam in an anterior-posterior direction. The image procedure utilized a polarized, vertically collimated energy source provided by the X15A beam line synchrotron located at Brookhaven National Laboratory. Following imaging of the intact lens, the lens was split sagittally and again placed perpendicular to the beam line for repeat image analysis.
The lens is clearly depicted by phase contrast imaging in both refractive and absorptive images. The lens periphery plainly demonstrates ringed structures indicative of change in refractive index among regions of lens discontinuity. The central lens region appears as a featureless form with a subtle concentric appearance. The images are remarkably crisp, however distinctive change in refractive indices through the bulk of lens organization is not fully resolvable.
Phase contrast DEI offers promise as a research tool to provide novel lens images in manner not previously visualized. However, current resolution may be below levels necessary to depict subtle refractive index changes characteristic of the lens. Although distinctive form is captured, further study is required to fully elucidate the character and pertinent lens related structural relationship of the images. Improvements in resolution are achievable and it may be possible to enhance lens images by altering the beam angle - lens orientation in conjunction with use of obliquely oriented transversely incised specimens.
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