Four in five cases of vision loss can still be treated
WHO estimates that about four-fifths of vision loss can still be prevented or cured—covering cloudy lenses, trachoma, river blindness, glaucoma, diabetic eye damage, and focusing problems left without correction. As of 2015, some 940 million people had vision loss: 246 million with low vision and 39 million blind, mostly over fifty in developing regions.
Visual impairment is partial or total loss of visual perception that, without eyewear, devices, or medical care, can block everyday tasks such as reading and walking. Worldwide, focusing problems left without glasses or contacts account for the largest share of cases, cloudy lenses for roughly a third, and glaucoma for only a small slice. Cloudy lenses top the list of causes of blindness; macular degeneration, diabetic eye damage, corneal clouding, childhood blindness, infections, and brain injury (cortical visual impairment) also matter. Child screening may improve later vision and schooling; routine screening of symptom-free adults has uncertain benefit.
In 2010 WHO switched from “best corrected” to “presenting” visual acuity in ICD-11 so uncorrected refractive error would no longer be overlooked. Categories run from mild (better than 6/18) through moderate and severe impairment to blindness grades down to no light perception. Legal definitions diverge: U.S. legal blindness is typically vision not correctable beyond 20/200 in the better eye, or a remaining field of 20 degrees or less—language rooted in a 1934 American Medical Association definition later written into Social Security rules.
Acuity alone poorly predicts daily function; someone at 20/40 may struggle while another at 20/200 manages if demands are low. Low-vision specialists use optical and electronic magnification, lighting, and contrast training to maximize residual sight; non-visual aids and braille support those with little or no useful vision. Rates of impairment have fallen since the 1990s, yet economic costs remain high through treatment spending and lost work. Temporary blackouts such as amaurosis fugax can signal serious disease and need urgent attention.
Source: Visual impairment
