Positive numbers on an eye prescription indicate they are correcting farsightedness, while negative numbers correct shortsightedness. A larger number suggests a stronger prescription.

Many people wonder how bad their eye prescription is, especially as the numbers and symbols are often difficult to interpret.

Although roughly 3 out of every 4 people in America require corrective lenses, according to research from the Vision Council, many do not understand what their eye prescription means.

In this article, we look at how to read an eye prescription and what the numbers mean.

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A person may require a different eye prescription for each eye.

The following tips can help people read their eye prescriptions:

  • Identify a + sign: Positive numbers, such as +1.00, explain how strong a lens needs to be to correct for farsightedness. Farsightedness means a person can see distant things but nearby objects appear blurry.
  • Identify a – sign: Negative numbers, such as -1.00, indicate the lens strength needed to correct shortsightedness. Shortsightedness is when a person can see close things but distant objects appear blurry.
  • A large number: Whether a + or -, a large number indicates a stronger prescription.
  • OS and OD: On an eyeglasses prescription, OS stands for Oculus Sinister, which refers to the left eye. OD stands for Oculus Dexter and refers to the right eye.
  • Eye differences: It is common for people to have different qualities of vision in their left and right eyes, particularly those with astigmatism.
  • Spherical correction (SPH): The spherical correction (SPH) refers to the lens strength needed to correct vision that affects the whole eye. This is usually the first number listed.
  • Cylindrical correction (CYL): Cylindrical correction is the second number and is only on prescriptions for people with astigmatism.
  • ADD: Some people need a different prescription to see things that re close by. ADD refers to the strength that the optician needs to add to a prescription to magnify objects.
  • AXIS: The axis notation tells lens makers where they should place the astigmatism correction in a lens.
  • PRISM: Eye doctors incorporate a prism into a lens to help correct problems with the eyes working together, such as one eye tilting inward while the other looks straight ahead.

A person with any questions about what their prescription means should speak to their optician who can answer any questions and help explain the numbers.

Eyeglass prescriptions change because people’s eyes change. Usually, these differences are not due to illness. For example, children do not fully develop the ability to focus both eyes on one object at the same time until they are 7 years old.

Children’s eyes continue to change rapidly as they grow, and children who wear glasses should see an eye doctor each year to make sure their eyeglass prescriptions continue to meet their needs.

Adults’ eyes also change, although more slowly.

Although not all older adults will have eye problems, several eye conditions have associations with age, including:

The most common age-related change is presbyopia. More than one-third of Americans experience this condition, which develops as the aging eye lens becomes less flexible and stiffer. People can start developing presbyopia when they are in their 20s.

As people age, the muscles that control the size of their pupils become weaker, which makes it more difficult for the eyes to adjust to changes in light.

The pupils generally become smaller, which makes it more difficult for a person to see in low light conditions, such as driving at night.

People can take steps to protect and enhance their vision. Key recommendations from the National Eye Institute include:

  • getting a dilated eye exam
  • adopting a healthy lifestyle, including being physically active, eating a varied diet, and not smoking
  • protecting the eyes by using contacts carefully, wearing sunglasses and protective eyewear when needed, and taking breaks from computer screens

According to the Centers for Disease Control and Prevention (CDC), 61 million adults in the United States face a high risk of vision loss, but only half of them have seen an eye doctor in the past year.

Regular, thorough eye exams play a crucial role in maintaining and improving vision because they can catch potential eye problems early. According to the American Academy of Ophthalmology, a complete eye exam should include:

  • dilating the pupils to permit a thorough examination of the eye
  • reviewing medical history
  • testing pupil health
  • performing a visual acuity test to determine an individualized prescription
  • performing a peripheral vision test
  • carrying out an eye pressure check, or tonometry
  • checking the retina and optic nerve
  • reviewing eye movement, also known as ocular motility, plus eye alignment and eye muscle health
  • checking lens, cornea, iris, and eyelid

People with the following conditions need to pay special attention to protect the health of their eyes:

  • diabetes — damage to the retina because of high blood sugar is one of the most preventable causes of vision loss
  • high blood pressure
  • a family history of eye problems

Anyone who notices changes in their vision should speak to a medical professional to ensure early diagnosis and treatment.

Anyone wondering how bad their eye prescription is can look at the numbers and notes on their prescription and interpret them using the above guide.

People who want further details or guidance can speak to a medical professional, such as an optician, for a detailed explanation.

People need to take care of their general health and have regular eye exams to protect their vision. Most eye changes and resulting revisions of prescriptions are due to the expected effects of aging.