If one is in the dark, Lumos would help him or her to see better.
In the epilogue in Deathly Hallows, while seeing their children off on the Hogwarts Express, Ron references a Supersensory Charm that allows him to park the car very easily, as the charm enhances vision. HP Lexicon This may not be exactly what you're looking for, though, as the Lexicon describes the charm as "[letting] the caster sense things out of his or her line of sight."
Although Hermione uses Impervius on Harry's glasses in Prisoner of Azkaban during a rainy Quidditch game, the spell doesn't affect Harry's eyesight per se -- it just keeps the rain from sticking to Harry's glasses. This spell is used in other contexts in other books. HP Lexicon
Mad-Eye Moody's magical eye is a strong demonstration of magic improving eyesight. In Order of the Phoenix, for example, Mrs. Weasley asks Moody to look through walls and into a desk to verify whether or not a Boggart is hiding there. Mad-Eye is able to do so and identifies it as a Boggart even though regular wizards have never known what a Boggart looks like in its natural state because it's a shape-shifter. I would imagine numerous intricate spells were used in the making of Moody's eye.
In Deathly Hallows, Harry allows Voldemort to kill him, and he finds himself in the King's Cross scene with Dumbledore -- he isn't wearing his glasses, nor does he need them. While in limbo, Harry can see perfectly without glasses. As the HP series is a Christian allegory series, there could be an implication of divine intervention here; whether one considers divine intervention to be a form of godly magic is going to vary person to person. I'm not saying it's either one way or the other, but just offering up the idea that death eases disability for the afterlife. I consider this a subjective topic, but it is HP canon and that's because of JKR's choice, not because of anything I did or thought of.
Conversely, there is a Conjunctivitis Curse that impairs eyesight -- Sirius suggests it to Harry during the Triwizard Tournament as a possible way to incapacitate the Hungarian Horntail during the first task. HP Lexicon