Squinting of the eyes is common, and is commonly done in an attempt to see better. If the eye has refractive error (like nearsightedness or farsightedness) the images entering the eye do not focus well on the retina and look blurry. By squinting and looking through the eyelashes, you can actually see a little clearer. The eyelashes turn the eye into a pinhole camera, which improves depth of focus and improves vision. Squinting is not a good long-term vision solution (obviously), so glasses or contacts are prescribed to improve vision and decrease eye strain. See the entry on pinholes to understand this concept better.