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Lydia Sauer, Sven Peters, Regine Augsten, Martin Hammer; Impact of Macular Pigment on Fluorescence Lifetimes. Invest. Ophthalmol. Vis. Sci. 2014;55(13):210.
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Macular pigment is known to attenuate the ocular fundus fluorescence by absorption of the short-wavelength excitation light. Fluorescence-lifetime-Imaging-Ophthalmoscopy (FLIO) is a new, non-invasive imaging method to study the human retina. Further investigations are necessary to asign measured lifetimes to specific fluorophores. In this study, we showed the impact of macular pigment on the fluorescence lifetime.
The time-resolved fundus autofluorescence of 20 healthy subjects has been recorded, using a prototype FLIO device (Heidelberg-Engineering, Heidelberg, Germany). Fluorescence decays were measured in two spectral channels (ch1: 490-560nm and ch2: 560-700nm) and approximated by a sum of three exponentials, t1, t2, and t3. Their amplitude-weighted means (tm) per channel and pixel were utilized as the main parameter for further statistical analysis. The macular lifetimes were averaged over a circular area of 1mm in diameter centered at the foveola. In parallel, the optical density (OD) of the macular pigment was measured with a fundus camera VisuCam (Carl Zeiss, Meditec Inc.). According to a standard protocol, the device provides the mean of the OD values as well as their integral over the fovea (volume). To prove statistically significant correlations for the obtained lifetimes and OD readings, the Pearson correlation coefficient (PCC) was employed.
An example of a color-coded fluorescence lifetime image (tm) is shown in figure 1. Tm in the short wavelength channel correlated significantly (p=0.012) to the mean OD with a Pearson correlation coefficient of -0.563. The correlation in ch2 did not show a significance (p=0.171; PCC=-0.328). In both channels, however, we found a significant correlation of tm to the OD-volume (ch1: p<0.001; PCC=-0.722 and ch2: p=0.004; PCC=-0.629).
In the retina of a healthy subject, fluorescence lifetimes are found to be shortest in the macular region (Schweitzer et al 2007, DOI: 10.1002/jemt). The revealed significant reduction of lifetimes with increasing macular pigment OD may explain this finding. However, further studies are required to elaborate whether Lutein or Zeaxanthin show fast decaying fluorescence or rather function as an optical emission filter by re-absorbing the autofluorescence of slow decaying components.
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