Temperature dependent fluorescence of A2-E, the main fluorescent lipofuscin component in the RPE

Purpose. A2-E is the dominant fluorophore of lipofuscin in the retinal pigment epithelium. In an in-vitro setup, we determined the temperature- dependent changes of the A2-E fluorescence with the aim of also assessing the potential value of such measurements for determining retinal temperature by autofluorescence measurements during laser treatment. Methods. A2-E was biosynthesized and diluted in Dimethyl Sulfoxide (DMSO) to 1 μM. Fluorescence measurements were performed with a photospectrometer under various temperatures ranging from 20°C to 75°C. Autofluorescence was excited at 467 nm, and emission was detected around 632 nm. Results. A2-E fluorescence intensity showed a linear decrease concomitant with temperature increment. At 75°C, the fluorescence intensity decreased by 43% compared to at 20°C. Fluorescence intensity was completely reversible dependent on the temperature, which cannot be explained by thermal A2-E alteration. Conclusions. If the A2-E temperature-dependent fluorescence in-vitro is transferable to human fundus autofluorescence, then it may be possible to apply an autofluorescence-based online detection device for noninvasive determination of fundus temperature during in vivo laser treatment. This is of clinical relevance, especially for the application of photodynamic therapy (PDT) and transpupillary thermotherpy (TTT).