Why do glasses seem perpetually smudged even when cleaned?

Because there is an incompletely transparent object between your eye and the world. While spectacle lenses are invaluable in correcting what eye doctors call Refractive Errors" such as myopia and astigmatism, they do so at a small cost in terms of visual quality. The front and back surface of any such lens, no matter how clean and unscratched, reflect a small amount of light and cause reflections. These are normally of little significance, especially compared to what the world may look like to a very nearsighted person. Furthermore, the further a spectacle lens is away from the natural focusing system of the eye (cornea, lens and retina) the more distortions are unavoidably created. The stronger a concave spectacle lens is, the smaller and further away it makes the object of regard. That is why the visual quality through contact lenses or after LASIK is more natural than through a spectacle lens even though all three may provide 20/20 visual acuity.

Written by J. Trevor Woodhams, M.D. - Chief of Surgery, Woodhams Eye Clinic