Is squinting really that effective?
Light enters the eye from many directions. The lens of the eye bends these rays so that they come together at a focal point. When the rays come together at the retina the image is in focus. If this focal point is in front of the retina, close objects are clear--nearsightedness; if it is behind the retina, distant objects are clear-- farsightedness.
Now, because they are bent more, the rays that pass near the edge of the pupil are blurred more. If you can eliminate these edge rays then you will have less blurring. That's what squinting does. It uses the eyelids to block the blurred rays that enter the pupil near its edge. Squinting is not a long-term solution to poor vision, but it sometimes helps in a pinch.