Blindness can be treated with a simple chemical injection into the eye, research has shown.
Scientists in the US used the approach to restore a level of vision to congenitally blind mice. They hope an improved version of the compound may help people with inherited and age-related forms of blindness.
The chemical, called AAQ, works by making normally "blind" cells in the retina sensitive to light. It was tested on mice with genetic mutations which left them blind within months of birth.
After injecting very small amounts of AAQ into the animal's eyes, the scientists were able to confirm restoration of some degree of light sensitivity.
The pupils of the mice contracted in bright light, and they showed evidence of light avoidance. This is a typical rodent behaviour that would be impossible without the animals being able to see some light.
Study leader Professor Richard Kramer, from the University of California at Berkeley, said the approach offered advantages over electronic chip or gene therapy treatments.
"The advantage ... is that it is a simple chemical, which means that you can change the dosage, you can use it in combination with other therapies, or you can discontinue the therapy if you don't like the results," he said.
"As improved chemicals become available, you could offer them to patients. You can't do that when you surgically implant a chip or after you genetically modify somebody."
Co-author Dr Russell Van Gelder, from the University of Washington, added: "This is a major advance in the field of vision restoration."
The research is published in the journal Neuron. New and better versions of AAQ are now being tested that activate neurons for days rather than hours, said Prof Kramer.