<unk> , also known as vision<unk> , is a medical definition primarily measured based on an individual's better eye<unk>  acuity; in the absence of treatment such as correctable eyewear, assistive devices, and medical treatment–<unk>  may cause the individual difficulties with normal daily tasks including reading and walking. Low vision is a functional definition of<unk>  that is chronic, uncorrectable with treatment or correctable lenses, and impacts daily living. 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. The American Academy of Ophthalmology defines<unk>  as the best-corrected<unk>  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. The term blindness is used for complete or nearly complete vision loss. The most common causes of<unk>  globally are uncorrected refractive errors (43%), cataracts (33%), and glaucoma (2%). Refractive errors include near-sightedness, far-sightedness, presbyopia, and astigmatism. Cataracts are the most common cause of blindness. Other disorders that may cause<unk>  problems include age-related macular degeneration, diabetic retinopathy, corneal clouding, childhood blindness, and a number of infections.<unk>  can also be caused by problems in the brain due to stroke, premature birth, or trauma, among others. These cases are known as cortical<unk> . 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. The World Health Organization (WHO) estimates that 80% of<unk>  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<unk>  benefit from vision rehabilitation, changes in their environment, and assistive 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<unk>  have decreased since the 1990s.<unk> s have considerable economic costs both directly due to the cost of treatment and indirectly due to decreased ability to work.
Visual impairment
Dyslexia
Vision disorder
Sexual dysfunction
Cognitive disorder
Cognitive deficit
Cortical blindness
Color blindness