Short-sight: Why is vision blurred?
The cause of short-sighted blur
In a normal eye light enters through the cornea, passes through the pupil (the natural opening in the iris) and continues through the lens located just behind the iris.
If there is no refractive error (a glasses prescription) the cornea and lens focus the parallel light rays to converge together to make a sharp image on the retina. This light-sensitive layer converts the light into information that passes along the optic nerve emerging from the back of the eye, taking the vision data to the rear part of the brain; the so-called occipital lobe then processes this information so that you get a visual perception and awareness of the world around you.
Myopia, the medical term for near-sightedness, is most commonly caused by growth of the eyeball, with the eye becoming longer from front to back. Often the front focusing part of the eye (the cornea and lens) is completely normal but the ‘screen’ where the image is projected onto is too far back. The image is now incorrectly in front of the retina, with the light rays crossing and continuing to form a blurred image.