270 Introduction to Anatomy & Physiology The classic Snellen chart is used to diagnose myopia. This familiar chart includes rows of letters, with each successive row smaller than the one above. The Snellen chart and other charts similar to it are used only as a first step in diagnosing myopia. Medical eye specialists perform a number of tests before they prescribe corrective lenses for visual defects. Laser surgery techniques also can be performed to correct myopia. Hyperopia The opposite condition is hyperopia (high- per-OH-pee-uh), also known as farsightedness. In hyperopia, the distance from the lens to the retina is shortened because the shape of the eyeball is more flattened (Figure 7.8C). Light rays focus behind the retina instead of directly upon it. As a result, objects at a distance can be seen clearly, but objects close up appear blurry. Prescription lenses can correct this condition. Presbyopia Presbyopia (prez-bee-OH-pee-uh) is an age-related version of farsightedness. Onset of presbyopia commonly occurs between 40 and 45 years of age because of changes that stiffen and discolor the lens of the eye. Presbyopia causes blurring of up-close vision that impedes the ability to read printed material or text on a computer screen. Like hyperopia, it can be corrected with prescription lenses. leungchopan/Shutterstock.com Figure 7.7 Have your eyes examined on a regular basis and as soon as possible if you experience any of the problems discussed in this lesson. Note that several problems can be remedied if treated early but can be very damaging if left untreated. © Body Scientific International Figure 7.8 Common vision disorders compared to normal vision. A—Normal vision. B—Myopia. C—Hyperopia. If light rays focus on a point in front of your retina, do you have trouble seeing objects close to you or far away? Refraction of light rays Refraction of light rays Refraction of light rays Focusing point on retina Focusing point in front of retina Focusing point behind retina A Normal vision: light rays focus on the retina B Myopia (nearsightedness): light rays focus in front of the retina C Hyperopia (farsightedness): light rays focus beyond the retina Retina Light Light Light Copyright Goodheart-Willcox Co., Inc.