United News of Bangladesh

Scientists have discovered how the human eye develops sharp central vision before birth, a finding that could pave the way for new treatments to restore sight in people with serious eye diseases. The study, led by researchers at Johns Hopkins University, found that a vitamin A-derived molecule works together with thyroid hormones to shape the retina during fetal development. The findings challenge a long-held theory about how the eye's light-sensing cells develop. The research was published in the journal Proceedings of the National Academy of Sciences. Researchers used retinal organoids—tiny pieces of retinal tissue grown in the laboratory from fetal cells—to observe how the human retina develops over several months. These organoids closely resemble the structure and function of the retina. The team focused on the foveola, a tiny area at the centre of the retina that is responsible for the sharpest vision. Although it covers only a small part of the retina, it accounts for nearly half of a person's visual perception. "This is a key step toward understanding the centre of the retina, which is often the first part of the eye to be damaged in people with macular degeneration," said Robert J. Johnston Jr., associate professor of biology at Johns Hopkins University and the study's lead researcher. He said the findings could eventually help scientists grow and transplant healthy retinal tissue to restore vision. The researchers examined cone photoreceptors, the specialised cells that allow people to see colours and objects clearly in daylight. These cells develop into blue, green or red cones, each detecting different wavelengths of light. Unlike the rest of the retina, which contains all three types of cone cells, the foveola contains only red and green cones. Until now, scientists were unsure how this unique pattern forms. The study found that during the 10th to 12th weeks of fetal development, a small number of blue cone cells first appear in the developing foveola. By around the 14th week, however, those cells change into red and green cones. According to the researchers, this process happens in two stages. First, levels of retinoic acid—a molecule produced from vitamin A—drop, reducing the formation of new blue cone cells. Then thyroid hormones trigger the remaining blue cones to transform into red and green cones. Johnston said the sequence is important because blue cones in the centre of the retina would reduce the sharpness of vision. The findings also challenge a theory that has guided vision research for about three decades. Earlier research suggested that blue cone cells formed in the centre of the retina before moving outward. The new study instead indicates that these cells stay in place but gradually change into red and green cones. Researchers say the discovery could eventually lead to new treatments for vision loss caused by diseases such as Age-related macular degeneration and Glaucoma, both of which damage the retina and can lead to blindness. The team is continuing to improve laboratory-grown retinal tissue so it more closely matches the human retina. Scientists hope these organoids can one day produce healthy photoreceptor cells for transplantation to replace damaged cells and restore lost vision. Researchers cautioned that the work is still at an early stage and more studies are needed to confirm the safety and effectiveness of such treatments before they can be tested in patients. Source: Science Daily