Written by Dr Jin Huang
Discipline of Biomedical Science, Sydney Medical School, The University of Sydney
Live imaging of ganglion cells using adaptive optics
Ganglion cells are the output nerve cells of the eye. This means they send signals to the rest of the brain for visual perception. That is how we see. Glaucoma is characterised by raised intra-ocular pressure which leads to ganglion cell death and blindness over time. Symptoms tend to appear after significant loss of ganglion cells coupled with impaired peripheral vision. If ganglion cells can be imaged over time, then early detection of their loss could lead to early treatments. This could slow down disease progression, preserve ganglion cell function and prevent further loss of vision.
Eye diseases such as retinal degeneration can be studied non-invasively using adaptive optics scanning light ophthalmoscopy. Adaptive optics were originally developed by astronomers to sharpen images by correcting the distortions in an image caused by turbulence in the atmosphere. In vision, adaptive optics compensate for distortions in the eye. This technique takes live images of cells in the retina such as photoreceptors, retinal pigment epithelial cells and blood cells in blood vessels. However, it is much harder to image ganglion cells as they are near transparent.
A recent study by Rossi and colleagues (PNAS, 2017) managed to image live ganglion cells in macaque monkeys and humans using a modification of confocal adaptive optics scanning light ophthalmoscopy. By combining images from different aperture positions, structural contrast was enhanced, and researchers were able to image individual cell bodies of ganglion cells. In the case of monkeys, even the nuclei within the cell bodies were visible. This resolution is currently not achievable for ganglion cell images taken from human eyes due to the need to use lower light intensity because of safety concerns. However, if similar resolution can be achieved with human eyes, then this technique could soon be used for early detection and examination of glaucoma.
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