As we age, so do our eyes; most commonly, this involves changes to our vision and new glasses, but there are more severe forms of age-related eye problems. One of these is age-related macular degeneration, which affects the macula — the back part of the eye that gives us sharp vision and the ability to distinguish details. The result is a blurriness in the central part of our visual field.
The macula is part of the eye’s retina, which is the light-sensitive tissue mostly composed of the eye’s visual cells: cone and rod photoreceptor cells. The retina also contains a layer called the retinal pigment epithelium (RPE), which has several important functions, including light absorption, cleaning up cellular waste, and keeping the other cells of the eye healthy.
The cells of the RPE also nourish and maintain the eye’s photoreceptor cells, which is why one of the most promising treatment strategies for age-related macular degeneration is to replace aging, degenerating RPE cells with new ones grown from human embryonic stem cells.
Scientist have proposed several methods for converting stem cells into RPE, but there is still a gap in our knowledge of how cells respond to these stimuli over time. For example, some protocols take a few months while others can take up to a year. And yet, scientists are not clear as to what exactly happens over that period of time.
Mixed cell populations
“None of the differentiation protocols proposed for clinical trials have been scrutinized over time at the single-cell level — we know they can make retinal pigment cells, but how cells evolve to that state remains a mystery,” says Dr Gioele La Manno, a researcher with EPFL’s Life Sciences Independent Research (ELISIR) program.
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