How does keratoconus affect vision?

Keratoconus causes blurry or distorted vision, which can be either blurry close vision or blurry long distance vision, but more commonly blurry long distance vision (or both!). This often starts in the teens or early 20s, and is due to increasing myopia and astigmatism.
In the early stages, this blurry vision can be corrected with glasses, but as the condition progresses vision with glasses becomes blurry too. Also, some people with keratoconus experience light sensitivity (photophobia) and glare, and even ghosting and double vision. RGP (rigid gas permeable) contact lenses are usually fairly successful in restoring clear vision.