Blue cones transform into red and green to build sharp vision
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- Johns Hopkins University researchers used lab-grown retinal organoids to identify that between fetal weeks 10 and 14, blue cones in the developing foveola convert into red and green cones, overturning a 30-year-old migration model.
- Retinoic acid, a molecule derived from vitamin A, is broken down to reduce new blue cone formation, then thyroid hormones drive remaining blue cones to switch identity into red and green cones, lead researcher Robert J. Johnston Jr. explained.
- The foveola — the tiny retinal region responsible for sharpest vision — contains only red and green cones and accounts for roughly half of all human visual perception, despite covering a small portion of the retina.
- The study, published in the Proceedings of the National Academy of Sciences, could improve organoid models of the foveola to enable future cell replacement therapies for macular degeneration and glaucoma, which currently have no cure.
- Researchers struggled to study this process earlier because common lab animals like mice and fish don't develop the same photoreceptor arrangement, making the human retinal organoid approach key to the discovery.
Why it matters: Macular degeneration is the first retinal region to fail in age-related eye disease and currently has no cure. If organoid models can be refined to produce transplantable, made-to-order photoreceptor cells — as the Johns Hopkins team is now attempting — patients with macular degeneration and glaucoma could eventually regain vision through cell replacement therapy, a treatment pathway that did not exist under the old migration model.
