Blindness

Overview

Blindness is the loss of vision that cannot be fully corrected with standard treatments like glasses, contact lenses, or surgery. It ranges from partial vision loss to complete blindness, with causes that may be genetic, congenital, or acquired over time. The severity and type of vision loss influence what accommodations or assistive technologies may be needed.

Classifications of Blindness

Blindness is classified in several ways depending on severity and cause.

Legal Blindness

Legal blindness is defined under U.S. law as having best-corrected visual acuity of 20/200 or worse in the better eye, or a visual field limited to 20 degrees or less. People classified as legally blind may still perceive light or shapes, but often experience significant difficulty with daily tasks.

Total Blindness

Total blindness means having no light perception (NLP). Individuals with total blindness cannot detect any visual stimuli, including light or movement. Though less common, it presents significant challenges and often requires tools like screen readers, tactile signage, and mobility training.

Partial Blindness

Partial blindness includes varying levels of usable vision. People may have blurred central vision, reduced peripheral vision, or trouble seeing in low light. Common causes include glaucoma, cataracts, and age-related macular degeneration.

Color Blindness

Color blindness is a deficiency in color perception, usually inherited, affecting the ability to differentiate specific color pairs (commonly red-green or blue-yellow). While it does not affect general vision, it can impact color-dependent digital content.

Congenital Blindness

This refers to vision loss present at birth, often due to developmental abnormalities of the eyes, optic nerve, or brain. Causes include genetic mutations, prenatal infections, and birth trauma.

Common Causes of Blindness

Common causes include genetic eye diseases (retinitis pigmentosa, Stargardt disease), infectious diseases (trachoma, HSV), macular degeneration, cataracts, diabetic retinopathy, and glaucoma. Each affects different parts of the eye and may lead to gradual or sudden vision loss.

Living With Blindness

Globally, over 2 billion people have some form of visual impairment. Approximately 43 million are completely blind. Adults with blindness often face barriers in employment and daily life. In the U.S., the ADA requires reasonable accommodations in workplaces, public spaces, and digital environments. Ensuring digital content is accessible—such as using alt text, heading structures, and keyboard navigation—plays a key role in supporting blind users online.