This change was made as newer studies showed that best-corrected vision overlooks a larger proportion of the population who has visual impairment due to uncorrected refractive errors, and/or lack of access to medical or surgical treatment. The previous definition which used "best corrected visual acuity" was changed to "presenting visual acuity". In 2010, the WHO definition for visual impairment was changed and now follows the ICD-11. Ī typical Snellen chart that is frequently used for visual acuity testing. Visual impairments have considerable economic costs both directly due to the cost of treatment and indirectly due to decreased ability to work. Rates of visual impairment have decreased since the 1990s. The majority of people with poor vision are in the developing world and are over the age of 50 years. 246 million had low vision and 39 million were blind. Īs of 2015 there were 940 million people with some degree of vision loss. Many people with significant visual impairment benefit from vision rehabilitation, changes in their environment, and assistive devices. This includes cataracts, the infections river blindness and trachoma, glaucoma, diabetic retinopathy, uncorrected refractive errors, and some cases of childhood blindness. The World Health Organization (WHO) estimates that 80% of visual impairment is either preventable or curable with treatment. Screening adults without symptoms is of uncertain benefit. Screening for vision problems in children may improve future vision and educational achievement.
These cases are known as cortical visual impairment. Visual impairment can also be caused by problems in the brain due to stroke, premature birth, or trauma, among others. Other disorders that may cause visual problems include age-related macular degeneration, diabetic retinopathy, corneal clouding, childhood blindness, and a number of infections. Cataracts are the most common cause of blindness. Refractive errors include near-sightedness, far-sightedness, presbyopia, and astigmatism. The most common causes of visual impairment globally are uncorrected refractive errors (43%), cataracts (33%), and glaucoma (2%). The term blindness is used for complete or nearly complete vision loss. The American Academy of Ophthalmology defines visual impairment as the best-corrected visual acuity of less than 20/40 in the better eye, and the World Health Organization defines it as a presenting acuity of less than 6/12 in the better eye. As such low vision can be used as a disability metric and varies based on an individual's experience, environmental demands, accommodations, and access to services.
Low vision is a functional definition of visual impairment that is chronic, uncorrectable with treatment or correctable lenses, and impacts daily living.
Visual impairment, also known as vision impairment, is a medical definition primarily measured based on an individual's better eye visual acuity in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment– visual impairment may cause the individual difficulties with normal daily tasks including reading and walking. Vision rehabilitation, changes in the environment, assistive devices ( eyeglasses, white cane) Uncorrected refractive errors, cataracts, glaucoma Non-24-hour sleep–wake disorder, falls in older adults A white cane, the international symbol of blindness