Blindness & Vision Impairment: Medical Vocabulary

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  • 0:00 Blind as a Bat
  • 0:37 Blindness
  • 2:13 Amblyopia & Scotoma
  • 3:41 Lesson Summary
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Lesson Transcript
Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

Do you know what blindness really is? Can you tell me both definitions for it? And have you ever heard of scotoma or amblyopia? I'm sure you have, as they have very common names you've heard of before.

Blind as a Bat

I don't know for sure where the phrase 'blind as a bat' came from, but bats can actually sense light and have a really great way of seeing, in their own way, in complete darkness when a person would otherwise be blind without something like a flashlight.

But what is blindness, anyways? Well, if you are like most people, you'd say that it's when you can't see anything at all. If you're a lawyer or an ophthalmologist, or inclined to be one, then the definition for blindness is a bit different.

Let's find out exactly what blindness is and define a couple of other terms related to partial vision loss.


Again, we can really define blindness in one of two ways. Blindness can either be seen, no pun intended, as:

  • The complete inability to see anything at all
  • Legal blindness, a state where vision is worse than 20/200 when corrected for with glasses or contact lenses

What is worse than 20/200? Well, you know that really famous Snellen eye chart? You know; the one with all those letters in rows?

At 20 feet away, if you have perfect vision, you'd be able to read the 20/20 line without a hitch. That really big E at the very top of the eye chart? That's the 20/200 line. People who are legally blind cannot even make out that gigantic E when standing 20 feet away from the eye chart, even with glasses or contact lenses. That's legally blind for you.

To put that into perspective for you, a person with 20/20 vision can read the big E 200 feet away, whereas a person who is legally blind can't read it, even with glasses, from 20 feet away. So, quite clearly, a person with such an impairment is justly considered to be legally blind even if they are able to sense light.

Causes for blindness in one or both eyes are many. They include trauma, something along the lines of King Harold II getting hit in the eye with an arrow, but in some alternative universe, somehow surviving. They also include diseases such as diabetes or conditions such as macular degeneration.

Amblyopia & Scotoma

Not all people who experience vision loss must be absolutely blind or legally blind. There are times when we may experience dimness of vision or a blind spot. Meaning, we lose some sense of vision.

For instance, amblyopia is dimness or decrease in vision with no apparent detectable disease or disorder of the eye itself. Sometimes this is called lazy eye. 'Amblyo-' means 'dull' or 'dim' and '-opia' refers to some sort of condition affecting vision.

Basically, this definition tells us that the eye itself is not sick. It looks normal. However, the person has reduced vision because the nervous pathways between the eye and brain don't work properly. This means one eye is favored by the brain over the other eye, the one that has poorer vision.

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