2-Photon-Excited Fluorescence SLO of the Human Eye

Article: Seeing the chemistry of vision
Source: Institute of Physical Chemistry, Polish Academy of Sciences (Poland)
Published: January 10, 2022

Two-photon-excited fluoresence of endogenous chromophores of a human retina
in three regions of interest (and with continuous wave scanning)

Advances in ophthalmic imaging modalities, such as optical coherence tomography (OCT), scanning laser ophthalmoscopy (SLO), and fundus autofluorescence (FA) have deepened our understanding of the mechanisms of eye diseases. However, some researchers argue that non-invasive assessment of metabolic processes occurring in retinal cells, such as of visual pigment regeneration, will become essential for eye diseases such as age-related macular degeneration (AMD), wherein cells in the early stage of a disease-altered retina cannot be distinguished from those of a healthy retina. Furthermore, fluorescent vitamin A derivatives, chemical intermediates of the process of light transduction, are highly sensitive to UV light, thus safe ways to analyze these markers are beyond current imaging instruments. In the present study, researchers in Poland, along with colleagues in the U.S. (at UC Irvine) developed a compact two-photon-excited fluorescence scanning laser ophthalmoscope (TPEF-SLO) and used it to spectrally resolve images of the human retina based on 2-photon excitation with near-infrared light. The instrument allowed the metabolites of vitamin A that are involved in vision, such as retinol or retinol esters, to be viewed in real time. Comparison between the eyes of two healthy human subjects and mouse models of retinal degeneration confirmed similar rapid accumulation of bisretinoid condensation products. The authors think that TPEF SLO imaging can be a noninvasive method to measure and quantify visual cycle intermediates and toxic byproducts of metabolic pathways leading to retinal degeneration. They state, "Noninvasive assessment of metabolic processes that sustain regeneration of human retinal visual pigments (visual cycle) is essential to improve ophthalmic diagnostics and to accelerate development of new treatments to counter retinal diseases...This approach opens the possibility for monitoring eye diseases in the earliest stages before structural damage to the retina occurs."

My rating of this study: ⭐⭐⭐

Boguslawski J, Palczewska G, Tomczewski S, et al. "In vivo imaging of the human eye using a two-photon excited fluorescence scanning laser ophthalmoscope." Journal of Clinical Investigation.  30 November 2021. https://doi.org/10.1172/JCI154218