https://www.scientificamerican.com/article/lab-grown-human-retinas-illuminate-how-eyes-develop-color-vision/

Sight begins when light bounces off surfaces and enters our eyes. The muscles of our pupils control how much light passes through, and the clear cornea and lens bend the light and focus it onto the retina, a thin strip of tissue covered in millions of light-sensitive neurons, or photoreceptors.

These nerve cells, named for the way they are shaped—like rods and cones—are where light is converted into electrical signals then sent via the optic nerve to the visual centers of the brain. A paper published October 11 in Science uses a retina grown outside the body to show how cones develop into the eyes’ color sensors.