Blindness

Blindness is a condition in which a person loses the ability to see to a degree that cannot be corrected by ordinary glasses or medical treatment. It can be total, meaning there is no vision or light perception, or partial, in which a person perceives some light and movement.

Vision works through a sequence: light passes through the cornea and lens, falls on the retina, and then the optic nerve transmits visual signals to the brain. Damage to any part of this sequence—at any stage—can result in blindness.

Definition and degrees

In medical terms, blindness and low vision are measured by visual acuity and visual field. Many people known as 'blind' retain some residual vision—for example, light perception or dim shapes. Therefore the term 'blindness' covers a wide range of conditions, not only complete darkness.

Causes

The leading causes worldwide include cataract (clouding of the lens), glaucoma (eye pressure that damages the optic nerve), retinal diseases related to diabetes, and uncorrected refractive error. Other causes are congenital, injury, infection, and malnutrition—such as vitamin A deficiency in children.

Daily life and tools

Blind people use Braille—a tactile writing system—canes for navigation, knowledge of familiar environments, and screen reader software. Mobile technology has expanded access to information and mobility.

Prevention

A large portion of blindness worldwide is considered preventable or treatable, particularly cataract and refractive errors corrected by glasses. Early screening, especially in people with diabetes and the elderly, can detect changes before they become permanent.