Is My Eye Prescription Bad? - What is Legal Blindness?

It’s very common for people to wear glasses or contact lenses to correct their vision. But how would you know if your vision is seriously impaired?

In this article, we’ll help you interpret your prescription, understand potential risks, discover practical steps to protect your vision, and learn what’s considered legally blind.

What Prescription is Considered Bad?

Different prescriptions refer to different levels of correction needed to restore normal vision. However, no eye prescription should be considered “bad”.

The American Academy of Ophthalmology uses the following benchmarks to classify the severity of nearsightedness (-) or farsightedness (+):

Mild. +/-0.25 to +/-2.00
Moderate. +/-2.25 to +/- 5.00
Severe. +/- 5.00 and above

What Does My Eye Prescription Mean?

An eye prescription is a written order for corrective lenses. An optometrist or ophthalmologist writes it.

An eye prescription includes:

Patient’s name
Date the prescription was issued
Expiration date
Specifications for vision correction
Prescriber’s name, contact number, and signature

The numbers indicate the level of severity of your nearsightedness or farsightedness. A 0.00 in your eye prescription means your vision doesn't need correction.

How to Understand Your Eye Prescription

The strength, or power, of your prescription is measured in diopters (D). Additionally, your prescription may include the following abbreviations:

OD. Oculus dexter (right eye)
OS. Oculus sinister (left eye)
OU. Oculus uterque (both eyes)
SPH. The strength of magnification in the lenses
CYL. Cylindrical correction, or the amount of lens power needed to correct astigmatism
AXIS. Indicates the angle of astigmatism correction
ADD. Shows extra lens power added for near-vision tasks in bifocal or progressive lenses.
PD. Pupillary distance measures the space between your pupils, ensuring your lenses align perfectly for clear, comfortable vision.

What Eye Prescription is Legally Blind?

The term "legally blind" actually comes from the government. The U.S. Social Security Administration (SSA) uses this term to determine who is eligible for certain disability benefits, tax exemptions, and low-vision training.

In the United States, a person has legal blindness if:

Their vision with glasses or contacts is 20/200 or worse
Their visual field is 20 degrees or less in the better-seeing eye

This means that a legally blind person has to stand 20 feet away from an object to see it with the same clarity as people with normal vision who can stand 200 feet away from that same object.

Common Causes of Legal Blindness

Many eye diseases can lead to legal blindness. The most common causes are:

Cataracts
Glaucoma
Age-Related Macular Degeneration (AMD)
Diabetic retinopathy

When Does Your Prescription Become a Health Risk?

Your prescription becomes more than just an inconvenience once it reaches certain thresholds. Here are the key risk points:

High myopia (-6.00 D and higher). Greater risk for retinal issues, such as retinal tears or detachment. Regular comprehensive eye exams become vital.
High hyperopia (+5.00 D and above). Increased potential for eye strain and angle-closure glaucoma, a serious eye condition.
Significant astigmatism (2.00 D or more). More likely to cause headaches and distorted vision, particularly during night driving.

Fortunately, these prescriptions can be managed effectively with the right corrective lenses.

Is It Bad if My Prescription Changes?

It’s normal for your eye prescription to change over time. As we age, our eyes experience gradual changes to visual acuity.

These changes can be caused by aging or other eye conditions, such as:

What Should You Do Next?

Your eye prescription is a helpful tool to determine your vision, but it’s not the only thing that dictates your overall eye health. Risks are associated with certain thresholds, not specific numbers alone.

Because of this, it’s important to get an eye exam at least once a year to catch the early signs of potential eye problems. You can also make certain lifestyle changes to improve your eye health.

These include:

Adequate sleep
Proper diet
Less screen time
Regular exercise
Avoiding smoking
Staying hydrated
Wearing sunglasses or protective eyewear

Treatment for Bad Eyesight

Treatments for bad eyesight include:

Eyeglasses. Consists of lenses that are tailored to address specific refractive errors.
Contact lenses. Thin, prescription lenses placed directly on the eye's surface and can serve as an alternative to eyeglasses.
LASIK Surgery. A refractive surgery that aims to reshape the cornea to correct vision problems.
PRK Surgery. Refractive surgery that reshapes the cornea but doesn’t involve creating a corneal flap.
Orthokeratology. A non-surgical treatment that uses specially designed, gas-permeable contact lenses worn overnight.