Abstract
Macular pigments (MPs), by absorbing potentially toxic short-wavelength (400-500nm) visible light, provide protection against photo-chemical damage thought to be relevant in the pathogenesis of age-related macular degeneration (AMD). A method of screening for low levels of MPs could be part of a prevention strategy for helping people to delay the onset of AMD. We introduce a new method for assessing MP density that takes advantage of the polarization-dependent absorption of blue light by MPs, which results in the entoptic phenomenon called Haidinger's brushes (HB). Subjects were asked to identify the direction of rotation of HB when presented with a circular stimulus illuminated with an even intensity of polarized white light in which the electric field vector was rotating either clockwise or anti-clockwise. By reducing the degree of polarization of the stimulus light, a threshold for perceiving HB (degree of polarization threshold) was determined and correlated (r2=0.66) to macular pigment optical density assessed using dual-wavelength fundus autofluoresence. The speed and ease of measurement of degree of polarization threshold makes it well suited for large-scale screening of macular pigmentation.
Highlights
Macular pigments are xanthophyll carotenoids of dietary origin
A method of assessing macular pigment density (MPD) that is suitable for mass screening could provide a valuable tool for informing people of their natural levels of protection so that they can be empowered to take preventative actions to further protect their eyes from violet/blue light and reduce other risk factors including smoking [20,21] and obesity [22,23]
This objective physical measurement approach employs confocal scanning laser ophthalmoscopy imaging with lasers at two excitation wavelengths: 486 nm, which is strongly absorbed by macular pigments, and 518 nm, which is weakly absorbed by macular pigments
Summary
Macular pigments are xanthophyll carotenoids of dietary origin. Of the 600 or more carotenoids found in nature, and 40–50 found in the human diet [1], only lutein, zeaxanthin, and meso-zeaxanthin are concentrated in a dense layer in the inner retina directly over the macula, where they intercept the path of light before it reaches the photoreceptors. An entirely new method of assessing MPD was proposed [25] that is based on the differential absorbance of polarized light by the MPs [26], which is central to the underlying mechanism responsible for the perception of the entoptic phenomenon known as Haidinger’s brushes [27,28] This psychophysical approach uses the subjects’ threshold for detecting Haidinger’s brushes (HB) as the degree of polarization (DoP) is decreased to assess the total amount of MP in the macula (see the Theory section below). We compared degree of polarization threshold to macular pigment optical density (MPOD) measured using dual-wavelength fundus autofluorescence
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