Solar irradiance spectra.

Visible range of the ASTM G173-03 solar irradiance spectrum, measured at a global tilt of 37° pointing to the sun (blue). The solar irradiance spectrum when not staring directly at the sun, including light scattered by the atmosphere and light reflected off the earth’s surface, is also shown (red).</p

Correlation between calibrated SW-AF measurements and histologic data on lipofuscin granules.

We considered the product of optical path length (l) and granule concentration (ng) to be indicative of light absorption by lipofuscin granules. Here, we tested whether this product correlates with calibrated SW- AF measurements published earlier (‘qAF8’ [28, 44, 45]), possibly allowing an estimation of this product (ng · l) in patients with STGD1 based on their qAF8 values. qAF8 values were measured in the posterior pole of the fundus (colored area in the inset). Blue dots represent average values of healthy people of different age-ranges; the red dot represents average values of patients with STGD1 (age P = 0.0259); therefore, a linear regression analysis was performed with data from healthy people (solid line). With the average qAF8 value of patients with STGD1, we extrapolated the value of (ng · l) in STGD1 prior to atrophy of the RPE (red dot).</p

Total rates of oxygen uptake by lipofuscin during light exposure.

<p>Rates of oxygen uptake (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172635#pone.0172635.g008" target="_blank">Fig 8</a>) were integrated along the wavelength of incident radiation to obtain the total rate of O₂-uptake, as an indication of cellular oxidative stress in-vivo during exposure to diffuse sunlight (white bars) or during SW-AF imaging (grey bars). X-axes: Age of healthy individuals, or patients with STGD1 (age, 20).</p

Optical screening by visual pigments (VP) in the outer segments of paramacular photoreceptors.

The wavelength-dependent single-pass optical density (OD) of light passing through the outer segments was calculated under conditions of daylight illuminance, amounting to 4400 photopic cd·m-2. See text for details.</p

Light attenuation by RPE-melanin in-vivo varies with age and the presence of Stargardt disease.

<p>We calculated the total optical density (OD) of paramacular RPE-melanin versus wavelength of incident radiation with Eqs <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172635#pone.0172635.e004" target="_blank">4</a>–<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172635#pone.0172635.e006" target="_blank">6</a> based on results of Monte-Carlo simulations. Colored lines indicate attenuation in healthy people of different ages: 20 (red), 40 (green), and 60 (orange). The same is shown for a 20-year old patient with STGD1 (black).</p

Relative contributions of light scattering and absorption by RPE-melanin.

<p>(A) Agreement between Monte-Carlo simulation and theory, plotted based on conditions in the paramacular RPE of a healthy 20-year old person. The optical density (OD) was calculated based on the product of the attenuation coefficient and the melanosome layer thickness (<i>l</i>_melanin). Attenuation by absorption (striped line), scattering (dotted line), and total attenuation (straight line) are plotted separately. The MC results are shown in blue (left Y-axis) and the theoretical result is shown in red (right Y-axis). See text for details. (B) Simulations of a thin (3 μm; blue) and thick (52.5 μm; orange) layer of melanosomes. In case of thicker layers, there is a dominance of the absorption coefficient (<i>μ</i>_{<i>a</i>, melanin}, straight lines) over the backscattering coefficient (<i>μ′</i>_{<i>s</i>, melanin}, striped lines) for all tested wavelengths.</p

Retinal exposure from diffuse solar irradiation compared to excitation light of short-wavelength retinal auto-fluorescence.

<p>At <i>λ</i> = 488 nm the peak height is indicated by single colored dots. Exposures were calculated by Eqs (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172635#pone.0172635.e002" target="_blank">2</a>) and (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172635#pone.0172635.e003" target="_blank">3</a>), respectively. Exposures in ocular media of different ages are plotted; 20 year-old (red), 40 year-old (green), and 60 year-old (orange).</p

Numerical simulation of oxygen uptake by lipofuscin in paramacular RPE in-vivo during exposure to diffuse sunlight.

<p>Oxygen uptake was calculated based on results from a previous investigation of oxygen uptake by isolated human lipofuscin granules [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0172635#pone.0172635.ref020" target="_blank">20</a>], after correction for factors affecting retinal exposure levels in-vivo (see text). Results were plotted for healthy people of different ages: 20-year old (red), 40-year old (green), and 60-year old (orange). Results for 20-year old patients with STGD1 are also shown (grey).</p

Monte-Carlo simulation of light scattering and absorption in a thick layer of melanosomes.

<p>In this plot generated by MontCarl, the optical paths (blue lines) of 3000 photons are ray-traced through a relatively thick layer of RPE-melanosomes at the concentration in-vivo. Photons are injected by an infinitely thin light beam at X/ Y = 0/ 0. The X- and Z-axes, respectively, indicate the lateral and vertical (depth) location in the sample. Most photons are either absorbed or scattered back at Z = 30 μm. At the assumed maximum in-vivo layer ‘thickness’ of RPE-melanosomes (3 μm), a small proportion of photons are backscattered or absorbed.</p