How Do We See?

show/hide words to know

Cataract: a condition in which a cloudy lens in the eye causes blindness.

Macular Degeneration: a condition caused by deterioration of the retinas; this is the most common cause of blindness.

What Causes Blindness?

Girl with sunglasses

You've probably been told not to stare at the sun. When you do, you overstimulate sensors on your retina, and they may not work as well anymore. Image by B & W girl portrait with sunglasses by Hamed Saber.

It might creep in without you even noticing. One day, you'll look around and things seem a bit...blurry. Don't worry, you are not alone. Most people have difficulty seeing clearly and must use glasses or contact lenses. This includes many older people as well. This is because their eye muscles do not work as well as they use to and cannot focus light into their eyes correctly.

What Does it Mean to Be Blind?

A lot of people think being blind means you live in a world of darkness. But that isn't always the case. Some people who can't see very well cannot use glasses to correct their vision  glasses won't help. Even if they are not completely blind, these people are referred to as Legally Blind.

What Causes Blindness?

Many diseases, illnesses, and infections can cause blindness. These affect the physical structure of the eye and can often be treated with medication or surgery. For example, many people will get cataracts when they get older, which occurs when the lens of the eyes becomes cloudy. People who have cataracts see things as if they were looking through a foggy window. Some types of cataracts are usually not permanent and can be fixed through surgery.
Dogs view with cataracts

Things might look blurry for someone with cataracts. Click for more detail.

Other types of blindness are permanent and may even worsen over time. For example, damage to the optic nerve will cause a disruption of visual information from the eye to the brain. This is a condition called "Optic Nerve Atrophy". It cannot be repaired because the optic nerve is deep in the brain where surgery is not possible.
The most common cause of blindness is “Macular Degeneration.” Macular degeneration occurs when the retina begins to pull away from the back of the eye. This disrupts the special sensors in the retina and sends confusing information to the brain.

Additional images via Wikimedia Commons. Refraction through glasses by Hackfish.

View Citation

You may need to edit author's name to meet the style formats, which are in most cases "Last name, First name."

Bibliographic details:

  • Article: What Causes Blindness?
  • Author(s): Page Baluch, Ashleigh Gonzales
  • Publisher: Arizona State University School of Life Sciences Ask A Biologist
  • Site name: ASU - Ask A Biologist
  • Date published: July 1, 2015
  • Date accessed: June 12, 2024
  • Link:

APA Style

Page Baluch, Ashleigh Gonzales. (2015, July 01). What Causes Blindness?. ASU - Ask A Biologist. Retrieved June 12, 2024 from

American Psychological Association. For more info, see

Chicago Manual of Style

Page Baluch, Ashleigh Gonzales. "What Causes Blindness?". ASU - Ask A Biologist. 01 July, 2015.

MLA 2017 Style

Page Baluch, Ashleigh Gonzales. "What Causes Blindness?". ASU - Ask A Biologist. 01 Jul 2015. ASU - Ask A Biologist, Web. 12 Jun 2024.

Modern Language Association, 7th Ed. For more info, see
refraction through glasses

Some people need to use glasses to see things clearly.

Be Part of
Ask A Biologist

By volunteering, or simply sending us feedback on the site. Scientists, teachers, writers, illustrators, and translators are all important to the program. If you are interested in helping with the website we have a Volunteers page to get the process started.

Donate icon  Contribute

Share this page:


Share to Google Classroom