AN IMPLANT that squirts chemicals into the back of your eye may not sound like much fun. But a solar-powered chip that stimulates retinal cells by spraying them with neurotransmitters could restore sight to blind people. Unlike other implants under development that apply an electric charge directly to retinal cells, the device does not cause the cells to heat up. It also uses very little power, so it does not need external batteries. The retina, which lines the back and sides of the eyeball, contains photoreceptor cells that release signalling chemicals called neurotransmitters in response to light. The neurotransmitters pass into nerve cells on top of the photoreceptors, from where the signals are relayed to the brain via a series of electrical and chemical reactions. In people with retinal diseases such as age-related macular degeneration and retinitis pigmentosa, the photoreceptors become damaged, ultimately causing blindness.