Sensorless adaptive optics optical coherence tomography for two photon excited fluorescence mouse retinal imaging

Two-Photon Excited Fluorescence (TPEF) is a common modality for volumetric imaging within a biological sample. The molecule-specific contrast of TPEF imaging of the retina enables novel in vivo studies of disease and retina physiology. Furthermore, retinal studies can be aided by imaging the relevant cells, which can be fluorescently labelled with fluorophores such as GFP. The multiphoton absorption suppresses the out-of-focus background signal and improves with the axial sectioning without a confocal aperture in the optical detection path. Imaging the retina with near infrared (NIR) light is ideal since the retina contain visual pigments that are sensitive to visible wavelengths and NIR light has less scattering within biological tissue than shorter wavelengths. However, high pulse energy is required to generate the TPEF, yet minimizing the incident exposure energy is required for non-invasive imaging. TPEF signal intensity increases quartically with the spot size, which leads to high sensitivity to aberrations that distribute the energy deposition of the focused light1. For retinal imaging, decreasing the spot size requires the imaging beam to fill a larger area of the eye, which corresponds to an increase in the aberration amplitudes and often results in low TPEF. Recent research has demonstrated improvements to the TPEF signal for retinal imaging using AO for aberrations correction2,3,4.