 Visual imperment, visual imperment, also known as vision imperment or vision loss, is a decreased ability to see to a degree that causes problems not fixable by usual means, such as glasses. Some also include those who have a decreased ability to see because they do not have access to glasses or contact lenses. Visual imperment is often defined as a best corrected visual acuity of worse than either 20 over 40 or 20 over 60. The term blindness is used for complete or nearly complete vision loss. Visual imperment may cause people difficulties with normal daily activities such as driving, reading, socializing, and walking. The most common causes of visual imperment globally are uncorrected refractive errors 43% cataracts 33% and glaucoma 2%. Refractive errors include nearsighted, farsighted, presbyopia, and astigmatism. Cataracts are the most common cause of blindness. Other disorders that may cause visual problems include age-related macular degeneration, diabetic retinopathy, corneal clouding, childhood blindness, and a number of infections. Visual imperment can also be caused by problems in the brain due to stroke, premature birth, or trauma among others. These cases are known as cortical visual imperment. Screening for vision problems in children may improve future vision and educational achievement. Screening adults without symptoms is of uncertain benefit. Diagnosis is by an eye exam. World Health Organization who estimates that 80% of visual imperment is either preventable or curable with treatment. This includes cataracts, the infections river blindness and trachoma, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness. Many people with significant visual imperment benefit from vision rehabilitation, changes in their environment, and assisted devices. As of 2015 there were 940 million people with some degree of vision loss. 246 million had low vision and 39 million were blind. The majority of people with poor vision are in the developing world and are over the age of 50 years. Rates of visual imperment have decreased since the 1990s. Visual imperments have considerable economic costs both directly due to the cost of treatment and indirectly due to decreased ability to work.