What Eye Prescription is Considered Bad?

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What Does My Eye Prescription Mean?

An eye prescription is a written order for corrective lenses, written by an optometrist, ophthalmologist, or optician. An eye prescription includes the patient’s name, the date that the prescription was issued, the specifications for vision correction, when the prescription expires, and the prescriber’s name, contact number, and signature.

An eye prescription may include any of 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 an astigmatism
  • AXIS: indicates the angle of astigmatism correction
  • ADD: addition, used for bifocal and multifocal lenses
How to read eyeglass prescription
eyeglass prescription for short sight

The numbers listed on the prescription refer to the focusing power prescribed. The unit of measurement is called a diopter. A positive number (indicated by a ‘+’ sign), indicates farsightedness, or hyperopia. A negative number (indicated by a ‘-’ sign) indicates nearsightedness, or myopia.

On an eye prescription, 0.00 represents good vision that doesn’t need focusing power. The numbers indicate the level of severity of your nearsightedness or farsightedness. Generally, the further away from zero (whether the number is positive or negative), the worse the eyesight and the greater the need for vision correction.

A number between +/-.025 to +/-2.00 is considered mild, a number between +/-2.25 to +/- 5.00 is considered moderate, and a number greater than +/- 5.00 is considered severe.

Eye prescriptions can change over time. Visual acuity, or sharpness of vision, may decrease gradually over time, caused by aging or other eye conditions such as astigmatism or amblyopia (lazy eye). Many adults experience presbyopia, or age-related farsightedness, as early as their 40s. Many gradual changes are normal as the flexibility of the natural lens changes over time.

Sudden, abrupt changes in vision, however, may be the sign of serious eye disease. If you experience a sudden dramatic change in vision, please visit your medical provider for an eye exam immediately.

Visual Acuity Chart
Visual Acuity Conversion Chart

What Eye Prescription is Considered Bad?

No eye prescription should be considered ‘bad’. However, different prescriptions refer to different levels of severity of correction needed to restore 20/20 eyesight, or normal vision. 

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

  • A number between +/-.025 to +/-2.00 indicates mild nearsightedness or farsightedness
  • A number between +/-2.25 to +/- 5.00 indicates moderate nearsightedness or farsightedness
  • A number greater than +/- 5.00 indicates severe nearsightedness or farsightedness

In most states, drivers need to have a 20/40 vision or better with vision correction for an unrestricted driver’s license. 

The World Health Organization uses the following benchmarks to categorize visual impairment:

  • Normal: 20/10-20/25
  • Near Normal visual impairment: 20/30-20/60
  • Moderate visual impairment: 20/70-20/160
  • Severe visual impairment: 20/200-20/400, or 11-20 degrees on visual field
  • Profound visual impairment: 20/500-20/1000 visual acuity, or 6- 10 degrees on visual field
  • Near-total visual impairment: Counting fingers, Hand motion, Light perception, or 5 degrees or less on visual field
  • Total visual impairment: No light perception 

What Eye Prescription is Considered Legally Blind?

The term "legally blind" actually comes from the government, not your doctor. 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.

Definition of Legal Blindness

In the United States, an individual has legal blindness if:

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

"Normal" vision is 20/20. This means that you can see an object clearly from 20 feet away. Someone with normal vision can stand 200 feet away from an eye chart and see it as clearly as a legally blind person sees it from a distance of 20 feet. A legally blind person's vision is at least 10 times worse than that of someone with normal vision.

Simulation of Visual Impairment
Simulation of Different Levels of Visual Impairment

However, some legally blind people have visual acuity better than 20/200, however, their peripheral vision is poor. People with normal vision have a lateral field view of almost 180 degrees. This means that they can see objects located directly to their left or right at the same time. If your visual field is only 20 degrees, your peripheral vision is reduced drastically. This is often called tunnel vision.

Is Astigmatism Bad?

Astigmatism is a common eye problem that causes blurry or distorted vision. This happens when the cornea or the lens of the eye has a different shape than normal. Astigmatism is a refractive error, like farsightedness or nearsightedness.

Common symptoms of astigmatism include:

  • Difficulty seeing at night
  • Eye Strain
  • Headaches
  • Blurred vision
  • Squinting to see clearly

Astigmatism is indicated on a prescription as part of the cylindrical (CYL) correction. If there is no number under CYL, it means there is no astigmatism, or the astigmatism is so slight that it doesn’t need to be corrected.

Mild astigmatism may not need to be corrected. But if astigmatism gets worse, it may be a sign of keratoconus or another serious eye disease. An eye doctor can determine if astigmatism requires treatment and what type of treatment is best. 

Astigmatism is commonly treated with eyeglasses and contact lenses. Laser surgery is also used to treat astigmatism. 

Treatment for Bad Eyesight

Medical professionals recommend that adults ages 19 to 40 with vision problems should get their eyes checked at least every two years. Adults older than 40 should get their eyes checked once a year.

Treatments for bad eyesight include corrective lenses or eyeglasses, contact lenses, LASIK surgery, low-dose atropine, and orthokeratology.

Common Questions and Answers

What does 20/200 eyesight look like?

A person with 20/200 eyesight needs to be within 20 feet of an object (or letters on a Snellen chart) to see it clearly. However, a person with normal vision can see the object clearly from 200 feet away.

What is the contact prescription for 20/200?

A visual acuity of 20/200 is roughly equal to a prescription of -2.50 diopters.

Eye doctors can't convert visual acuity (like 20/200) to an exact prescription, they can only give you a rough idea. Many different uncorrected prescriptions can yield a visual acuity of 20/200. The only way to know for sure is to have your eye doctor check.

Is 20/400 considered legally blind?

If you have a visual acuity of 20/200 or worse (after putting corrective lenses on), you are considered legally blind. If the glasses or contacts improve your visual acuity, you are not legally blind.

A visual acuity of -4.00 is roughly equivalent to 20/400 vision. A person with 20/400 eyesight needs to be within 20 feet of an object to see it clearly. However, a person with normal vision can see the object clearly from 400 feet away.

Is +1.25 eye prescription bad?

A +1.25 prescription (which means you are farsighted) is a mild refractive error. Glasses, contacts, or even LASIK can easily correct this condition.

My contact prescription is -6.50, am I legally blind?

It depends. A contact prescription of -6.50 does not mean you are legally blind if your vision improves from 20/200 with them in. However, if you still have 20/200 eyesight or worse after putting contacts in, you are considered legally blind.

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Resources
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“Astigmatism: MedlinePlus Medical Encyclopedia.” MedlinePlus, U.S. National Library of Medicine, https://medlineplus.gov/ency/article/001015.htm

“Changing Vision? How to Make Sure Your Eyes Are Healthy.” University of Utah Health, https://healthcare.utah.edu/the-scope/shows.php?shows=0_tae12e39

“Comprehensive Eye Exams.” AOA.org, https://www.aoa.org/healthy-eyes/caring-for-your-eyes/eye-exams?sso=y

“How to Read Your Eyeglass Prescription.” The Canadian Association of Optometrists, 18 June 2018, https://opto.ca/health-library/how-to-read-your-eyeglass-prescription

“Low Vision and Vision Rehabilitation.” AOA.org, https://www.aoa.org/healthy-eyes/caring-for-your-eyes/low-vision-and-vision-rehab?sso=y

“Nearsightedness: MedlinePlus Genetics.” MedlinePlus, U.S. National Library of Medicine, 18 Aug. 2020, https://medlineplus.gov/genetics/condition/nearsightedness/

“Nearsightedness: Myopia Diagnosis and Treatment.” American Academy of Ophthalmology, 26 June 2020, https://www.aao.org/eye-health/diseases/myopia-nearsightedness-treatment

“What Does 20/20 Vision Mean?” American Academy of Ophthalmology, 11 Feb. 2020, https://www.aao.org/eye-health/tips-prevention/what-does-20-20-vision-mean

Your Prescription Explained. Association of Optometrists, www.aop.org.uk/advice-and-support/for-patients/your-prescription-explained.

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