Although these results suggest that the modulation of singlet oxygen has an impact on the frequency of nonviable, A2E-laden RPE after blue light illumination, we were also intrigued by the proclivity for intracellular A2E to undergo fluorescence quenching under blue light (data not shown). To begin to investigate this observation, A2E in aqueous media was exposed to 430 nm illumination (0.095 mW/mm
2, 10 minutes), and A2E was quantified by HPLC. The HPLC profile revealed a decrease in the absorbance of the A2E peak, denoting a loss of A2E after blue light illumination, compared with the control nonilluminated sample
(Fig. 2) . This decrement in A2E was attenuated, however, when the sample was incubated in oxygen depleter to reduce oxygen before 430-nm illumination
(Fig. 2) . The FAB-MS spectra of blue-light-illuminated A2E revealed not only a molecular ion peak at a mass-to-charge ratio (m/z) of 592, corresponding to the molecular mass of A2E (C
42H
58ON),
36 but also a series of additional molecular ion peaks (e.g., m/z 608, 624, 640, 656, 672, 688), each of which differed from its neighbors by mass 16
(Fig. 3) . Moreover, the extent to which these derivatives of A2E were formed was dependent on the intensity of illumination. Thus, when the spectra derived from irradiances of 0.075, 0.095, and 0.15 mW/mm
2 were compared, it was apparent that as the irradiance increased, the higher-mass peaks became prominent, and additional peaks at m/z 656, 672, and 688 appeared. Concomitant with these spectral differences, the intensity of the A2E peak at m/z 592 was diminished
(Figs. 3C 3D) , consistent with the light associated reduction of A2E observed by quantitative HPLC
(Fig. 2) and fluorescence microscopy (not shown).