As shown in Fig. 1(a), a super-continuum laser (SC-400 Fianium, Southampton, U.K.) is used as the light source for the SLO subsystem. By changing bandpass filter 1, different excitation wavelengths can be chosen. Currently, a dual-band bandpass filter (FF01-482/563, Semrock, Rochester, NY) is placed in the laser beam to restrict the light source spectrum to two spectral bands, providing strong excitation for green fluorescent protein (GFP) and mCherry, respectively, delivering a total of at the mouse pupil. A single bandpass filter (MF469-35, Thorlabs, Newton, NJ) delivering was used if only GFP-band excitation was desired. Emitted fluorescent light was separated by a dichroic mirror, DM1 (Di01-R488/561, Semrock, Rochester, NY) and collected by two photomultiplier modules, PMT2 and PMT3 (H7422-40 and H7422-50, respectively; Hamamatsu, Nagoya, Japan). Bandpass filters 2 and 3 (FF01-525/45 and FF01-609/54, Semrock, Rochester, NY) were used to further restrict the emission bands collected by PMT2 and PMT3 for GFP and mCherry, respectively. A reflected light signal was acquired by PMT1 (H7422-20 Hamamatsu, Nagoya, Japan). By flipping mirror M1 in and out of the beam, the light can be directed into spectrometer2 (QE65000 Ocean optics, Dunedin, New Zealand) to measure the fluorescence emission spectrum; when operating in spectrometer mode, the SLO can operate either in “point excitation” (no scanning) or “region of interest (ROI)” (scanning) mode, though the recorded spectral information in the latter mode arises from the entire ROI. A photo of a mouse positioned for imaging is shown in Fig. 1(b).