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Visiting an eye doctor is no longer the only way to receive a prescription for glasses. Many online tools and services can provide a person with this information, but these should not substitute a visit to an ophthalmologist or optometrist.

Eyeglass prescriptions have different signs and letters that tell opticians and eyeglass lens makers which type of lens a person needs to correct their vision. This includes ‘+’ and ‘-‘ signs, a spherical number, a cylinder number, and more. A person may also notice an infinity sign or “plano (Pl).”

This article looks at everything a person needs to know about online tools and services to help them order a new pair of prescription glasses or contact lenses.

The following are some general tips on how to read prescriptions for eyeglasses.

Learn more about how to read eyeglass prescriptions here.

‘+’ and ‘-‘ signs

These signs signify whether a person has long- or shortsightedness. Some people may also know longsightedness as farsightedness or hyperopia, and shortsightedness as nearsightedness or myopia.

A ‘+’ sign means that a person has longsightedness. A ‘-‘ sign means that a person has shortsightedness.

Spherical number

The spherical number, or SPH, is how strong a lens needs to be to correct a person’s vision. These numbers will have a “+” or “-” sign above them depending on if a person is long- or shortsighted.

A person may notice an infinity sign or “plano (Pl)” on their prescription. This means that the person does not need prescription lenses.

Cylinder number and AXIS

The cylinder number, or CYL, notes whether a person has astigmatism. This number can either be positive or negative.

The AXIS will be a number between 1-180. This shows the position of astigmatism.

Opticians will not fill out these fields if a person does not have astigmatism.


Opticians are likely to fill out the ADD field for people who require bifocals or varifocals and need a prescription for reading.


These two fields relate to whether a person has a muscle imbalance in their eyes.

A PRISM number will often be in fractions, such as 1 1/2.

The BASE field will have directions, such as up, down, in, and out.

Pupillary distance (PD)

PD is the distance between a person’s pupil center points.

It is important to know the PD, especially if a person intends to purchase glasses online. The PD helps to ensure the glasses fit correctly and the lenses center on the eyes.

Vision examinations play an important role in keeping the eyes and eyesight healthy and clear. For the average person, the American Academy of Ophthalmology (AAO) recommends that adults get an eye exam as follows:

  • ages 18–39 — 1 time
  • ages 30–39 — 2 times
  • age 40 — full comprehensive exam to check for vision changes and early signs of eye conditions
  • ages 65 and over — once every 1–2 years

The American Optometric Association (AOA) recommends that children follow a different schedule to test for vision changes and to spot any early signs of eye problems:

  • birth to 2 years — test 6–12 months
  • 3–5 years — at least once
  • 6–17 years — before 1st grade and then yearly

Some people need more regular eye examinations. The AAO states that the following groups should have more frequent eye examinations:

  • people who wear contact lenses (who should test once per year)
  • people with an infection, vision changes, or injury to their eye
  • those with a family history of eye disease
  • those living with diabetes
  • people with high blood pressure

Comprehensive eye exams

During a comprehensive test, an eye doctor looks at various aspects of a person’s eyesight. According to the AOA, a person can expect the following from a comprehensive eye exam:

  • a full medical history
  • visual acuity
  • keratometry/topography that measures the curve of the cornea
  • preliminary tests that check various aspects of vision, such as muscle movement, color vision, peripheral vision, and other exams
  • eye health evaluation
  • how the eye focuses or moves
  • refraction, to measures the power needed in corrective lenses

Following an exam, the optometrist will provide a person with a prescription. In some cases, they may fill the prescription in the doctor’s office. Others may wish to use their prescription to purchase their glasses or contact lenses online or in a different store. Individuals who do not intend to buy from their doctor’s office should request a copy of their prescription. The eye doctor is legally required to provide this information at no added cost.

People who are confident their vision has not changed or recently had an eye examination but cannot find their prescription may start by asking their doctor for a copy, as they should have the prescription on record.

If an individual cannot receive a copy or their prescription has expired, and they are unable to visit their eye doctor’s office to renew it, they can instead take advantage of online tools that can help determine their last prescription.

Retailers, such as GlassesUSA, provide free smartphone apps that scan a person’s current pair of glasses to determine their last prescription.

It is important to remember that at-home tests should not replace a medical eye exam or comprehensive eye exam carried out by a licensed optometrist or ophthalmologist.

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A person looking to order new glasses with a current and valid prescription can consider some of the following companies for their prescription needs:

  • GlassesUSA smartphone application. The app allows people to use their smartphone’s camera to scan their current glasses to determine their existing prescription.
  • SmartBuyGlasses offers a similar tool to GlassesUSA, allowing people to scan their current glasses to get their prescription information.

For a sight test that results in a new prescription, a person may consider the following options:

  • Visibly: For a small fee, a person can get an online eye exam that can provide a prescription from an optometrist or ophthalmologist within 24 hours. Unlike GlassesUSA, this is an actual vision test a person can use at home.
  • lensabl: Again, for a small fee, a person can take an at-home vision test and receive a prescription from an ophthalmologist within 24 hours.

To get started, a person needs to visit the Prescription Scanner page on the GlassesUSA website. From there, they can click download the scanner app to their smartphone.

According to the company’s website, a person needs to have the following to hand to use the free app:

  • a smartphone with the app installed
  • a computer
  • a magnetic credit card for size calibration
  • their current glasses

The app contains instructions to follow, and the process takes 10–15 minutes. An individual holds both the glasses and smartphone in different positions so the app can get an accurate reading of the prescription from the glasses lenses. They can then use the prescription information to order a new pair of glasses.

The app is best suited to:

  • overall healthy individuals who are aged 18 or older
  • those with a single-vision prescription between -6.00 and +3.00
  • people with stable vision and are happy with their current prescription
  • cylinder measurement lower than -2.50

What information does it provide?

According to GlassesUSA, their tool provides the optical parameters from a person’s current glasses. It will provide enough information to order a new pair of glasses with the same prescription lenses as their current pair.

Is the information reviewed by a qualified healthcare professional?

No. According to GlassesUSA, the information provided in the app is private. The app uses an algorithm to find a person’s current prescription and pupil distance (PD). The app does not test a person’s eyes or detect any new eye conditions.

Who is the GlassesUSA scanner app not suitable for?

GlassesUSA advises that their prescription scanner app is not suitable for those who:

  • take medications for vision
  • use a bifocal, progressive, or multifocal prescription
  • have a high single-vision or astigmatism prescription
  • have conditions or illnesses that affect eye health
  • have a prescription with a prism measurement

A person who is not a good candidate for this tool should talk with their eye doctor. They may need to schedule an eye exam. A person nearing their next appointment should wait to order new glasses to make sure their script has not changed.

An online tool to scan for a prescription can save a person time and money, but it is not the best option for everyone. It is also not a substitute for preventive care visits to an eye doctor.

Regular eye exams are important for detecting early signs of several eye diseases and disorders. An eye exam can identify the following conditions:

By getting regular examinations, an eye doctor may find and begin treating conditions early. Early treatment can help prevent vision loss.

Eye care and contact lenses

Wearing contact lenses with the correct prescription is essential, and a person cannot purchase contact lenses without a valid and current prescription. This is a legal requirement within the United States, as the Food and Drug Administration (FDA) classify contact lenses as medical devices and regulate the production and sales processes of contact lenses.

According to the AOA, when a person wears contact lenses, they will typically require an annual visit to their eye doctor. However, an individual’s eye doctor will confirm an appropriate exam schedule.

Below are some commonly asked questions about finding eyeglass prescriptions.

How can I find out my eye prescription?

A person should always request their eyeglass or contact lens prescription from the office that performed their last eye exam.

If people cannot access their prescription there are several companies who can provide one if a person has an up-to-date prescription lens.

Can I figure out my eye prescription online?

People can use apps, such as GlassesUSA’s app, to find out their eyeglass prescription.

Alternatively, for a small fee, some websites offer an online eye exam. This may be more suitable for people who do not have a current prescription.

If a person does not have a copy of their eyesight prescription, they can first contact their eye doctor for this information, as they are required to provide a copy free of charge.

If an individual is confident that their prescription has not changed and would like a new pair of prescription glasses, they may take advantage of online tools, such as lens scanners. The tool can determine a person’s prescription and allow them to order new glasses from their home.

Other online services offer similar tools or even allow a person to take a vision test at home for a new or renewed prescription. Not everyone is a good candidate for an online tool or online sight test, and these services do not replace visits to an eye doctor.

Anyone choosing to use an online lens scanner or other tool does so at their own risk as there is no scientifically backed evidence to support their accuracy.

People who need a comprehensive exam or have an eye injury or infection should make an appointment with their optometrist or ophthalmologist.