As light enters our eye it passes through the cornea – the transparent skin over the iris and pupil – and the lens. Like glancing arrows, the light rays are bent into focus. They shoot across a clear, gel-filled chamber and strike a layer of light-sensitive cells that line the back of the eye. This is the retina, where the true alchemy begins. The light triggers a cascade of chemical and electrical impulses that race along the optic nerve to the brain, which creates an image – vision. However retinal problems such as age-related macular degeneration – the leading cause of visual impairment in the UK – can lead to blindness. But scientists have managed to grow a human retina from stem cells, which could be used to halt or reverse vision loss. Here, stem cells in the lab-grown retina have differentiated into photoreceptors (stained green) that respond to light.
Written by Nick Kennedy
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.
BPoD is also available in Catalan at www.bpod.cat with translations by the University of Valencia.