When wearing the glasses, the user is able to see events shortly before they happen as well as giving some degree of foreseeability in terms of making choices.
Marina allows Ella to wear the glasses in order to make her feel more involved in the team, on the journey to find Number Eight. Ella soon notices a rocket flying towards them, though the others can't see it. Sure enough, the rocket comes into view and the group are forced to jump from the moving van. Ella also uses the glasses to look at possible paths to take towards Eight, the others cannot tell the difference between each path but Ella is able to correctly choose the right path.
During Eight's test of Ella, she forsees that the glasses are knocked off her face and destroyed before it happens, causing her to scream out. The glasses are then swiped off of her face and crushed by a falling tree branch, something Ella feel responsible for.