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H. S. Ginis, I. Pentari, A. Pennos, I. G. Pallikaris; Intensity and Angular Distribution of Light Scattering From Corneal Tissue at Different Hydration States. Invest. Ophthalmol. Vis. Sci. 2010;51(13):5647.
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It is known that corneal edema is associated to increased light scatter. It was the purpose of this study was to accurately measure the narrow angle forward scattering properties of corneal stroma at different hydration levels using a sensitive optical technique.
Sixteen freshly enucleated porcine eyes were obtained from a local abattoir. The corneas were deepithelialized using a mechanical brush and the central 8 mm of each cornea were harvested using a Barron's PKP trephine. Corneal buttons were rinsed with saline and immersed for at least 3 hours in Dextran (300kDa) solutions with concentrations ranging from 5 to 20% w/w. For light scattering measurements the samples were mounted in purposely built holder with glass lenses enclosing firmly the corneal sample. This triplet served as a lens for a CCD camera. Scattered light measurements were performed in angles ranging from 8 arcmin to 17 degrees using circular stimuli on a computer screen. Before scatter measurements the thichness of each corneal sample was measured by means of a mechanical pachymeter (Mitutoyo IDC 112T, Japan). Corneal hydration was estimated by weighting the corneal samples and combing this measurement with one additional weight after each samples had been dried overnight in vacuum at a temperature of 60 degrees C. Scatter coefficient was determined as the fraction of energy of the PSF at angles wider than 10 arcmin divided by the equivalent number for a diffraction limited system.
The mean scatter coefficients for the samples at normal hydration levels was 0.22 (SD=0.059). This value was effectively double (0.46 ; SD= 0.048) at a moderate increase of stromal thickness by 17% and reached a value of 0.56 (SD=0.079) at a relative increase of corneal thickness of 62%. The angular distribution did not significantly depend on hydration.
As expected, scattered light in the cornea increases with edema. In the present study, it was documented that even small changes in corneal hydration affect significantly the narrow angle light scattering properties of corneal stroma.
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