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David DeVries, Melanie C W Campbell, Laura Emptage, Chris Cookson, Marsha Kisilak, Francisco J. Avila, Juan M Bueno, Rachel Redekop, Matthew Wilson; Polarization properties of amyloid beta deposits in ex vivo human retinas from those with Alzheimer’s disease differ from surrounding retina. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):2385.
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© ARVO (1962-2015); The Authors (2016-present)
Alzheimer’s disease (AD) is diagnosed from plaques composed of insoluble fibrils of amyloid beta (Aβ) in the brain. Aβ has been found near the optic nerve fibre layer of the retina by us in those with AD using fluorescence staining. We have shown that some polarization properties of presumed Aβ deposits and pure Aβ differ from surrounding areas. The neural retina is optically accessible so polarization properties could enable non-invasive detection of Aβ deposits in the living eye. Here we characterize additional polarization properties of Aβ deposits which produce contrast, including retardation.
Retinas were dissected from eyes obtained following informed consent and fixed in paraformaldehyde or formalin for those with a diagnosis of AD and age matched normals without AD or glaucoma. The retina was stained with 0.1% Thioflavin-S, (which is polarization insensitive) and measured using a Nikon transmission microscope fitted with a polarimeter. The Mueller matrix (MM) describes the interaction of a sample with states of polarized light. It is calculated from 16 images. Polarimetry images were taken of regions, -ve and +ve for Aβ deposits. Spatially resolved MM of the areas and then their false colour images of polarization properties were calculated. These properties included degree of polarization, diattentuation, polarizance, and retardance. Paired t-tests compared the properties of +ve and -ve areas in AD +ve retinas and unpaired t-tests compared them with areas in control retinas.
28 deposits and nearby -ve areas were characterised in 3 retinas, +ve for AD, as well as areas in 3 control retinas. As previously reported by us, degree of polarization, diattentuation and polarizance produced some contrast of the deposits. Across all deposits, degree of polarization (p<0.0008) and retardation (p<0.0005) gave significantly different mean values between areas with and without deposits and compared to control retinal areas. Retardation values of deposits were well above those reported for the optic nerve fibre layer in ex vivo retinas. Related indices were also explored for the sensitivity and specificity of using polarization imaging to detect the deposits.
The measurement of polarization properties is a promising non-invasive and inexpensive method of locating and tracking Aβ deposits in the retina as a biomarker of AD.
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