Refractive error is a problem with focusing light onto the retina due to the shape of the eye.  The most common types involve near-sightedness (myopia), far-sightedness (hyperopia), and astigmatism (uneven focus of light). Presbyopia is a condition beginning around age 35, causing progressive difficulty with viewing near objects.  This typically results in a need to hold items further and further away in order to read. Refractive error and presbyopia cause blurry vision, headaches, and eye strain, and can be corrected with eyeglasses.

    Comprehensive Ophthalmology