Results from a phase 2 trial of phenytoin were published in the Lancet in January 2016. Researchers found that those taking phenytoin had 30% less damage to the retina (the light sensitive nerve fibre layer at the back of the eye), compared with those taking a placebo. This suggests that phenytoin could protect nerves from damage.
The trial involved 86 people who were experiencing early symptoms of acute optic neuritis. They took either phenytoin or a placebo for 13 weeks .