Deprivation of vision during critical periods of childhood development has long been thought to result in irreversible vision loss. Now, researchers from the Schepens Eye Research Institute/Massachusetts Eye and Ear, Harvard Medical School (HMS) and Massachusetts Institute of Technology (MIT) have challenged that theory by studying a unique population of pediatric patients who were blind during these critical periods before removal of bilateral cataracts. The researchers found improvement after sight onset in contrast sensitivity tests, which measure basic visual function and have well-understood neural underpinnings. Their results show that the human visual system can retain plasticity beyond critical periods, even after early and extended blindness. Their findings were recently published in the Proceedings of the National Advancement of Science (PNAS) Early Edition.
"Our research group has been studying the development of vision in children who were blind from birth because of congenital cataracts. We have been measuring if and how their vision develops after surgery in late childhood and adolescence to remove cataracts, which enables sight for the first time. Our results show remarkable plasticity and vision continues to improve in many children long after the surgery," said Senior Author Peter J. Bex, Ph.D., Senior Scientist, Schepens Eye Research Institute/Mass. Eye and Ear and Associate Professor, HMS Department of Ophthalmology.
The authors explain the research: Project Prakash is a joint scientific and humanitarian effort led by Pawan Sinha, Ph.D., full professor at MIT. The humanitarian part aims to address problems of treatable blindness in India by providing surgeries free of cost to children with cataracts. In the Western world, children born with cataracts typically are treated in the first year of life, but children with this condition in rural India often go untreated because their families lack the necessary financial resources. The project also aims to answer the questions: can children who suffer from extended congenital blindness develop vision after cataract surgery and if so, how does this process happen?
The "critical period" or the "critical window" is a traditional concept in the field of neuroscience that suggest that there is "plasticity," or potential for development, early in life. But as we grow older ― and in the case of vision, pass the age of 7 or 8 ― there is less and less plasticity in the visual system.