Purchase this article with an account.
A. E. Elsner, D. A. VanNasdale, B. P. Haggerty, J. A. Papay, M. J. Cannon, C. J. Kenrick, S. A. Burns; Aging and the Scattered Light Ratio in Confocal Polarized Light Imaging. Invest. Ophthalmol. Vis. Sci. 2008;49(13):888. doi: https://doi.org/.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
To probe structural changes to the retina with age that are too early or subtle to be visualized as distinct features using a novel metric of scattered light. To determine if this metric, the scattered light ratio, is related to aging in carefully selected, normal subjects.
We used scanning laser polarimetry to separate reflected light from scattered light. We acquired 3 sets of 15 deg, macular-centered images using a GDx with 780 nm illumination (Zeiss). A pinhole before each detector minimized scattered light anterior or posterior to the retina. Each set is 20 raw images, differing in input polarization, from the crossed detector and 20 from the parallel detector. The scattered light ratio is the proportion of light that was depolarized by multiple scattering. Thus, the grayscale of the light not modulated by polarization (the minimum) was computed from crossed detector data for each pixel. Assuming that scattered light reaches both detectors equally, this ratio is (2 X the minimum of the modulation)/(average light return). This ratio removes the effects of reflectivity of retinal and subretinal structures, instrument laser power or gain, or alignment variation. Samples at 1 deg from the fovea from 30 normal subjects, aged 15 - 30 yr, were compared to a group 50 - 75 yr. To quantify repeatability, the best data set was "Measurement 1," and the second best was "Measurement 2."
The scattered light ratio at 1 deg was 0.16 for the younger group and 0.25 for the older group, using Measurement 1. The older group had significantly more scattered light, as expected (P < 0.0001). Measurements 2 ratios were also 0.16 and 0.25, without a significant increase in variability for either group.
At 1 deg from the fovea, there is significantly more scattered light on average in healthy older retinas than in the younger retinas. This increase in light scattering has a potential impact on vision. Despite low absorption of near infrared light, the majority (75% or more) of light in healthy eyes was not multiply scattered, given carefully focused, polarized light and a small confocal aperture. Thus, a change in the distribution of scattered light may provide a sensitive method for detection of pathology.
This PDF is available to Subscribers Only