Label-free imaging of bipolar cell axons in mouse retina by second-harmonic generation

Here we present label-free imaging of retinal bipolar cell axons by second-harmonic generation microscopy. The nonlinear optical signal arises from uniformly polarized microtubules, providing a surrogate contrast for the functional integrity of axons. The unique properties of microtubule SHG from the inner plexiform layer were employed for testing an outstanding hypothesis in glaucoma, namely, the persistence of BC axons in the disease during a critical period when the synaptic connections to the retinal ganglion cells are lost.