Imaging method reveals long-lived patterns in cells of the eye

My lab is interested in
imaging the eye, one of the only places where
you can look inside the human body
and see a complete tissue, full of neurons, epithelial
cells, and vasculature. When light enters the eye,
it gets focused down to the back of the eye, on a thin layer of tissue
called the retina, where it gets detected by
a specialized neuron called a photoreceptor. These photoreceptors don’t
exist all by themselves, but require the nourishment
of a surrounding cell, called the retinal pigment
epithelial cell, or RPE. RPE cells have historically
been very difficult to image, because they contain pigment. And so any light that enters
the eye gets captured and absorbed by the retinal
pigment epithelial cells, making it difficult to image
them using optical techniques. We’ve developed a new way
to image the RPE based on the use of an
existing FDA-approved dye called indocyanine green,
or ICG. This dye is injected
intravenously, where it travels up to the eye and is taken up rapidly
by the RPE cells. After a relatively
uniform uptake, it settles into a heterogenous
pattern, with neighboring cells having different amounts of
fluorescence. And this heterogeneity
is what enables us to distinguish neighboring
cells from each other. Surprisingly we found that
with a repeat injection, one year later
in the same eye, that the same pattern
was formed. And so we could use this
fluorescent signature as a way to track the eye
across time, at a cellular level. To acquire these images we use
a technique called adaptive optics, which is a
technique that allows us to image at a cellular-level
resolution inside the eye. Because we deploy our
instrument in a clinical setting, we have
access to a special population
of patients, including a patient with
Bietti crystalline dystrophy, a disease that is thought
to affect the RPE. We found in a shorter
timespan of 7 months that there was a change in
the fluorescent signature of the RPE,
indicating that the RPE was likely to be disrupted
in the early stages of disease. We’re currently exploring
different ways to translate this technology to the clinic, where it can be more
readily accessible.

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