If left untreated, the clouding lens symptom caused by cataracts completely impairs vision, according to the American Academy of Ophthalmology. Worldwide, cataracts are responsible for about 51 percent of all blindness, the World Health Organization states. Cataracts most typically develop as part of the aging process.
In 2010, cataracts were the cause of blindness in about 20 million people across the globe, according to the WHO. The high incidence rate is due to limited access to cataract surgery in many parts of the world.
Other symptoms of cataracts include blurred or double vision, poor night vision, and sensitivity to light and glare, reports Mayo Clinic. People sometimes notice rings or halos around lights, and colors seem faded or yellowed. Glasses or contact lens prescriptions need to be updated frequently. Because cataracts grow slowly, vision loss is not always noticed until a cataract is fairly large.
Cataracts are typically not removed until they interfere with daily life, the AAO states. Until that point, it's standard practice for vision to be corrected with new prescriptions. More than half of Americans 80 and over have developed cataracts, and many of them have had corrective surgery, reports MedlinePlus. When a cataract is removed, an artificial lens is inserted in place of the clouded natural lens, Mayo Clinic explains.