The Elves in Rings of Power and Lord of the Rings were known for their superior eyesight. There have been three examples of this thus far, two from the Rings of Power and one from Lord of the Rings. When Galadriel traveled with the Numenoreans to Middle Earth, she encountered Isildur on deck and asked him if he came up to catch the first sight of land. She then told him he should see it in a few moments, while she had noticed it for the past hour. Elrond visited his friend Durin at Khazad-dûm, and from a great distance, he followed the conversation between Durin and his wife Disa. In Lord of the Rings, there is the scene in which Aragorn, Legolas, and Gimli are traveling through Rohan. Legolas is able to recognize details of a rapidly-moving group of horsemen from five leagues away. Clearly Tolkien’s Elves had eyesight far more acute than humans.
In order to consider the question of how far the Elves could see, the process of seeing needs a rough explanation. In basic terms, light from an object travels and moves through the lens of the eye, which focuses an image on the retina. As this light passes through the narrow opening of the pupil, it spreads out. How far away the object is helps determine the clarity of the image perceived with the eye. Almost all eyes function in this way, and the eyes of the Elves in Rings of Power and Lord of the Rings shouldn’t be any different.
But they are different. Galadriel could see what Isildur could not, and Elrond was able to spy on his friends. Aragorn, in Lord of the Rings, « saw a shadow on the distant green, a dark swift-moving blur, » but Legolas saw the details. In the Tolkien canon, these were matters of fact, and as such they couldn’t have human-like eyes. Larger, anime-style eyes could have greatly improved vision, but they were out because in both the books and Lord of the Rings and Rings of Power, the Elves did not have saucer-sized eyes. Nor did they have eagle-eyes, which are the best all-around design as eyes go. Elves were unique creatures, and attempts at sussing out how far they could see just don’t add up. They could see as far as Tolkien wanted them to see.
Elves were conferred with many special abilities. They were gifted with immortality, though many would argue that’s no gift. They did not fall prey to age or disease. As an adjunct to their superior vision, they were able to see creatures of shadow, such as the Ringwraiths. Some had the power of healing, and others could conjure protection for their lands. Perhaps the most incredible ability the Elves possessed was their skill at crafting magical things. The Silmarils, heavily featured in Tolkien’s Silmarillion, were made by the Elves. Their importance in the lore was only rivaled by Sauron’s ring. Galadriel’s mirror, the Palantiri, and lembas bread were all works of the Elves. They made good use of their long lives.
In Lord of the Rings and Rings of Power, the Elves are shown to have abilities that humans do not. This raised questions of how far could they actually see and how powerful were they really. J.R.R. Tolkien created a vast legendarium full of fascinating races and compelling stories that have long outlasted him. Elves in various Tolkien lore were figures of wonder, and his depictions of their capabilities in Lord of the Rings and his other works had more to say about how they viewed and reacted to the world than whether they could see a man on a horse five leagues away.