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All About Eye Prescription: What the Numbers Mean

When you visit for an eye check-up, you'll mostly see letters and numbers on your 'scorecard' recorded by your doctor. In most cases, they will discuss the results of your test with you, but you're also curious about what those numbers and other details mean. It's daunting to memorize all of them, so here's a guide to the essential letters on your eye prescription. This may come in handy when you want to understand your prescription better and discuss your results with your doctor.

details of eye prescription

Why does correct eye prescription matter in choosing glasses?

An accurate eye prescription is essential in choosing your eyeglasses, as it helps you see things and people more clearly. You might have noticed that before your doctor finalizes your vision score and provides an eye prescription, they let you try wearing different lenses and ask for feedback if you feel dizzy or see blurred vision when using such lenses. This process ensures they can provide the correct eye prescription. As you know, strong or weak prescriptions will affect your vision quality.

Here are other reasons why a correct eye prescription is necessary.

  • Avoid dizziness. Without the right eye prescription, wearing your eyeglasses for long hours can make you dizzy and feel like you have vertigo. The wrong prescription distorts the visual field, which may result in nausea or dizziness.
  • Fewer headaches. The wrong prescription on the eyeglasses puts your eyes in so much hard work trying to correct the images that are being perceived. In short, you're stressing your eyes too much, which could result in more frequent headaches. An accurate eye prescription takes away all these issues.

If you still have discomfort or poor vision with the right eye prescription, it may be related to another vision concern.

A glossary of eye prescription abbreviation

  • OD refers to oculus dexter or the right eye.
  • OS refers to your left eye or the oculus sinister.
  • OU means both eyes and the oculus uterque.
  • NV or near vision. This is the amount of power needed for a more effortless reading experience.
  • DV refers to distance vision. The details and numbers here indicate whether the patient is farsighted or nearsighted.
  • PD stands for pupillary distance. Binocular PD refers to the distance from one pupil to another; meanwhile, Monocular PD means the distance from the pupil to the middle of the nose.
  • SPH refers to the sphere or the lens power needed to correct the eyesight.
  • CYL means cylinder or the amount of astigmatism in the patient's eye.
  • AXIS refers to the number between 1 and 180, which indicates where astigmatism appears in the patient's eye. The axis and the cylinder help correct astigmatism.
  • ADD is the additional lens power required for patients to read easier. This number is usually reflected on a prescription for reading glasses. It could also be seen on the lower portion of progressive or bifocal lenses.
  • BO, BU, BI, and BD refer to base out, base up, base in, and base down. The details under these abbreviations will tell the eyewear manufacturer where to exactly position the prism on the glasses, which will correct double vision.
  • Prism is used by eye doctors for patients with double vision. It indicates the amount of prismatic power needed to correct the differences in the eyes' alignment.
  • Diopter refers to the unit of measurement used to calculate the focusing strength of contact lenses or eyeglasses. In short, it indicates how strong the patient's eye prescription is.
  • Positive (+) numbers mean that the patient is farsighted. Sometimes, eye doctors provide numbers without the plus sign, which signifies the same condition.
  • Negative (-) numbers mean that the patient is nearsighted.

When does an eye prescription expire?

An eye prescription generally expires one to two years after your prescription was written. The expiration could also depend on the state where you're in. Remember that every state has laws to regulate when an eyeglasses prescription expires. Also, some people are prone to having quicker changes in their vision; thus, eye doctors will most likely write prescriptions with expiration dates sooner than what is imposed by the law. For example, a prescription for a child with myopia, which gets worse each year, might expire after a year rather than after two years.

Prescriptions for your eyeglasses relatively expire to help ensure you have the best vision possible and that the eye health condition is at its most optimal. Eye conditions like glaucoma may occur with few to no symptoms. Through a comprehensive eye check-up when the prescription expires, you are checking your vision and overall eye health.

How often should you get a new pair of glasses?

Eye doctors and experts advise that all eyeglasses must be replaced once every two to three years, but there are other points to consider besides the common timeframes. Some glasses need replacements every year, while others could last more than three years before they are replaced. If you're uncertain how often you must replace your eyeglasses, a few essential milestones and indicators below might help.

  • You're having blurred vision. You might need to replace your lenses if your vision is blurry while wearing your prescription eyeglasses. Blurred vision also calls for an eye exam to update your eye prescription.
  • You squint to see things. Squinting is another indicator to replace your old eyeglasses. You don't need to squint and strain your eyes on regular days to see, especially when using your prescription glasses.
  • Headaches. As mentioned in this article, frequent headaches after a long day of wearing your eyeglasses already call for a glasses replacement. Experiencing headaches indicates you're overworking your eyes too much to see things properly.
  • Poor eyeglasses condition. Cracked lenses and scratched lenses, missing screws, and faded and foggy lenses mean that you must get new eyeglasses as soon as possible. These glasses conditions will only cause hassle and poor vision when you wear your worn-out eyeglasses.