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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
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.
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.
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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 has several benchmarks of visual impairment. These are defined by when the vision in the better eye with vision correction is below a certain threshold. Any vision below 20/70 with corrective lenses is considered visual impairment.
What Eye Prescription is Considered Legally Blind?
In the United States, an individual is considered “legally blind” if their vision with glasses or contacts is 20/200 or worse.
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
- 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.