What is Bad Eyesight? [And What is Legally Blind?]

Millions of people around the world wear glasses and contacts for bad eyesight. But that term is so broad that it covers everything from mild farsightedness to those who are legally blind.

But what is actually considered bad eyesight? And when is it considered legally blind?

We’ll answer both these questions and more in our full guide below.

What is normal or 20/20 vision?

Normal vision (or normal visual acuity) is typically 20/20, which means you can read the eighth row of a Snellen eye chart at a distance of 20 feet.

See this in action in the video below from VSP Vision Care’s Youtube channel.

Only about 35% of adults have 20/20 vision, and not every deviation from that number causes concern or need for correction. But you need at least 20/40 vision to pass an eye test to drive without corrective lenses.

The higher the second number, the stronger correction you need.

What is Bad Eyesight?

The World Health Organization categorizes visual impairment in the below categories:

• Normal (20/15-20/25)
• Near-normal (20/30-20/60)
• Moderate (20/70-20/160)
• Severe (20/200-20/400)
• Profound (20/500-20/1000)
• Near-Total/Total (beyond 20/1000)

Is Your Eyesight Bad?

Based on the above chart, generally “bad eyesight” is classified as “Severe” and above or 20/200.

But as we mentioned above, bad having a severe prescription or bad eyesight doesn’t mean much in today’s world. Especially with a large number of corrective lenses available.

How do you know if you have Bad Eyesight?

Usually, the most common sign of decreased eyesight is difficulty reading, seeing faces or road signs, or blurry vision. If you have visual issues that cause difficulties with your daily activities, it’s time to see an eye doctor.

If you have a sudden loss of vision, headaches, or recent injuries, you should contact your doctor immediately.

What causes Bad Eyesight?

To start, a better term for bad eyesight is visual impairment. And the most common visual impairments are caused by refractive errors or health conditions in our eyes.

Refraction refers to the way our eyes bend light. And a refractive error simply means that our eyes are not bending light properly, leading to unclear vision.

Generally, there are three types of refractive errors:

• Nearsightedness (myopia)
• Farsightedness (hyperopia or presbyopia)
• Astigmatism (an imperfection in the curve of your cornea or lens)

Luckily these are all correctable with glasses or contact lenses

When it comes to medical and health conditions, there is a variety of eye diseases that can affect your vision, but the most common are:

1. Old age and cataracts – Usually developing slowly, Cataracts cloud the lens of your eye
2. Glaucoma – A typically hereditary group of eye conditions that cause eye damage and vision loss to the nerve in the back of your eye
3. Age-Related Macular degeneration (AMD) – The gradual degeneration of your retina usually causing blind spots and blurred vision typically due to age or family history
4. Smoking – While not normally tied to your eyes, studies have found more signs of Macular Degeneration and Glaucoma symptoms in smokes compared to non-smokers

What is a Legally Blind Prescription?

You’re considered legally blind if your vision on an eye test is 20/200 or greater, with correction.

Now let’s clarify.

That doesn’t mean if you’re prescription is greater than 20/200 you’re legally blind. As we mentioned above, 20/200 vision is common criteria for bad eyesight. But it’s still completely correctable in most cases.

Instead, you are legally blind if, after correction (meaning glasses or contacts), you still have 20/200 vision.

A very general guideline would be that moderate to severe corrections of +/- 2.50 or greater would be necessary for someone with visual acuity of 20/200 or worse.

You may also be considered legally blind based on your visual field, which measures peripheral vision.

If you have a visual field of fewer than 20 degrees without moving your head, that is also considered an indication of legal blindness.

What Does 20/200 Eyesight Look Like?

If you have 20/200 vision, only the top E on a standard eye chart will be legible without correction (and probably only because you recognize the shape).

You would need to stand 20 feet from an object to see it clearly that someone with 20/20 vision could see from 200 feet.

Contact Lens Prescriptions for 20/200 Visual Acuity

Contact lens prescriptions are not the same as those for eyeglasses. Because a contact lens sits directly on your eye, you need a different prescription than for a corrective lens that sits some millimeters away.

Like eyeglasses prescriptions, the only way to know what your contact lens prescription should be if your visual acuity is 20/200 or greater is to see your eye doctor.

How to Read an Eyeglasses Prescription

Eyeglass prescriptions are full of acronyms and numbers. We’ve included the one you need to know in the section below. And for more information, check out our full guide on How to Read Your Prescription.

Here’s how to decipher this sometimes mysterious code.

Abbreviations to Know

OD = Right Eye

OS = Left Eye

SPH = Sphere. This measurement tells you if you are farsighted (numbers have a (+) plus sign) or nearsighted (numbers have a (-) minus sign). And how powerful the lens needs to be to correct your vision in each eye.

The sphere number may also be followed by a letter “D”, which stands for diopter. This is the unit of measure for corrective lenses.

CYL = Cylinder. Cylinder tells you if you have astigmatism with larger numbers indicating more astigmatism.

Axis = Orientation of your astigmatism on your cornea. This is a number between 0 and 180.

Add = Any extra lens powers. This is used for multifocal lenses.

Final Thoughts

There is no one-size-fits-all definition of bad eyesight.

Caring for your eyes includes more than an eye exam, so everyone should visit the eye doctor at least every other year. And if you’re over 65, make that appointment every year.

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