OUR EYES, unlike other organs hidden deep within our bodies, sit in plain sight. They have been inspirations for artists, symbols for the superstitious, and objects of scientific fascination for centuries. In ancient Greece, medical pioneers cut them open in public dissections, revealing delicate layers of retina, cornea, and iris. In the early 10th century, Persian physician al-Razi discovered that the pupil dilates and contracts to control the amount of light that enters. Six centuries later, the Renaissance-era anatomist Vesalius sketched a cross-section of the orb—with some errors. But eyes themselves are imperfect: Just one fault could cause the whole organ to glitch or break down. 

It turns out that flaws are common in our vision. More than 7 million Americans have some form of vision loss, which can include partial or full blindness, according to a 2021 analysis of 25 years of data from the US Census, the Centers for Disease Control and Prevention, and others. Many of these conditions are present from birth. Mutations in particular regions of DNA can lead to incorrectly formed optical parts. This can distort a person's sight, especially if the issues are in the retina, the layer of cells at the back of the eye that captures incoming light and transmits it to the brain. But what if we could give someone with limited vision a corrected version of their genetic material to fix the malfunctioning parts?