Refractive errors are one potential cause of blurred vision. The most common refractive errors are myopia (nearsightedness), hyperopia (farsightedness) and astigmatism (distorted vision); it is possible to have more than one refractive error at a time.
A myopic eye is longer than normal or has a cornea that is too steep, so that the light rays focus in front of the retina. Close objects look clear, but distant objects appear blurred.
A hyperopic eye is shorter than normal. Light from close objects cannot focus clearly on the retina. The words on a page will seem blurry, or it will be difficult to see well enough to do close-up tasks, like threading a needle.
Astigmatism distorts or blurs vision for both near and far objects. It’s almost like looking into a fun house mirror in which you appear too tall, too wide or too thin. When you have astigmatism, the cornea curves more in one direction than in the other – like a football. A normal cornea is round and smooth, like a basketball.
Adapted from the American Academy of Ophthalmology