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Ashwin Sampathkumar, Matin Khoshnevis, Jeffrey A Ketterling, Alfredo A Sadun, J Sebag; Optical Characterization of Vitreous with Multi-Wavelength Photon Correlation Spectroscopy (MWPCS). Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):384.
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© ARVO (1962-2015); The Authors (2016-present)
Age-related vitreous degeneration with posterior vitreous detachment and myopic vitreopathy are often accompanied by symptomatic floaters due to altered vitreous morphology. While floaters reduce contrast sensitivity and disturb vision, asteroid hyalosis (AH) is often asymptomatic, even when advanced. It is hypothesized that floaters are bothersome because of irregular surface morphology, while asteroid bodies are not disturbing because of smooth surfaces. This study developed instrumentation and analytics to measure light scattering to test this hypothesis.
Vitreous was modeled using solutions of type II collagen (Coll; .1%, .05%, .03%, .01%, .005%, .003%, .001%, and hyaluronan (HA; .25, .15, .075, .025, .015, .0075, and .0025μg/μl). The two were combined at concentrations of .01% Coll & .025μg/μl HA. AH was modeled with solutions of 75µm and 150µm microspheres, both individually and combined at concentrations ranging from .01% to 2.5%. The on- (α) and off-axis (β) scattering coefficients of all solutions were measured by MWPCS using broadband light that was collimated to the samples in cuvettes in an integrating sphere. The forward on-axis and lateral off-axis scattered light was collected using two spectrometers. Peaks in the off-axis spectra indicate surface irregularity of the structures in solution.
On-axis scattering of Coll, HA, Coll+HA and microsphere solutions declined with increasing concentration, up to a threshold beyond which multiple scattering produced pronounced non-linear trends (Fig 1). Off-axis measurements showed distinctive scattering peaks in the spectra, indicative of surface irregularities in vitreous model solutions, whereas measurements in the AH model (microsphere) solutions showed less scattering and smoother trends.
This MWPCS system detects variable light scattering as a function of concentration. Further, light scattering in model vitreous solutions was consistent with the hypothesis that the surface morphology of vitreous structures is irregular, influencing light scattering in a manner that would interfere with vision. Microspheres, however, had less pronounced effects owing to their smooth surface morphology and spherical shape. These results suggest utility for this approach in evaluating light scattering by various vitreous disorders.
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