prescription test

Eyeglasses 101—Understand Your Prescription and Eyeglasses

Written by Kalysta Law | September 14, 2020

girl going through an eye exam

Just came back from the eye doctor, with an eyeglasses prescription in hand, yet still confused about what everything means? Whatever the optician mentioned seemed like a foreign language? If all you know is that you can’t see and need some help from glasses, we’ve got you covered. Eyewear not only serves as a fashion accessory to enhance your style but more importantly, it is a medical device for vision correction purposes. The prescription is the recipe to build your perfect pair of eyeglasses; the lens material, coating, and style come together to give you the best vision benefits. Before you decide to buy prescription eyeglasses from your eye doctor directly or order glasses online, we are here to equip you with all the basics you need to make a good decision.

First and foremost, it is important that you get your eyes checked regularly. If you have gotten an eye exam in the past, eye care professionals are required to provide you with a copy of the prescription, which should have an expiration date required by state law, eg, 1 year, 2 years, etc. If you do not already have a prescription, it is very important to pay your optometrist a visit as a valid prescription is required for anyone to legally sell you eyeglasses or contact lenses. If you are a contact lens user or plan to use them, you might ask, “are my contact lens prescription different than my eyeglasses prescriptions?” The answer is yes, they are in fact, different since contact lenses sit directly on top of the eye. Make sure you’ve got the correct prescription!

Prescription (Rx)

handwritten prescription for eye glasses or contacts

Now that you are all checked, let’s start to understand what the abbreviated terms and the sequence of numbers say about your vision and how it affects your choice of eyewear.

What is OD and OS?

To begin reading your prescription, the first step is to understand what OD and OS mean. O.D. is an abbreviation for the Latin term Oculus Dexter, which means “right eye.” All information listed in this row will be used for the right eye. O.S. is an abbreviation for the Latin term Oculus Sinister, which translates to “left eye.” All items listed in this row will be used to correct the left eye. Some prescriptions might also have a row labeled O.U., an abbreviation for Oculus Uterque, which means “both eyes.”

What do the numbers stand for?

SPH (Sphere)

The column labeled SPH is the abbreviation of the sphere, this conveys the power of correction that will be put on the lens. It is measured in diopter (D), which will usually be in quarter increments, for example, 0.25, 0.75, 1.00, etc. This is prescribed to correct myopia (nearsightedness) or hyperopia (farsightedness). If the number under this column starts off with a minus sign (-), it is meant to correct nearsightedness; if the number follows a plus sign (+), it is meant to correct farsightedness.

CYL (Cylinder)

While the sphere power is to correct nearsightedness or farsightedness, the cylinder indicates the amount of lens power to correct astigmatism. When someone has astigmatism, it means that the cornea is curved differently in one direction than the other. The cylinder number corrects the irregular curve in the eye.


If cylinder power is put on the lenses, it must be followed by an axis to specify where the correction should be applied. The axis power measures from 1 to 180 degrees, with 90 degrees corresponding to the vertical meridian of the eye.

Add (Reading Addition)

As the name suggests, the numbers in this column are for additional reading power when needed. The power would be added to the reading area of the lens, which means this is most likely a multifocal/bifocal eyeglasses prescription.


Prism is used to correct certain eye conditions such as muscular imbalance, lazy eye, or eye alignment problems. Prismatic power is measured in prism diopters (p.d.), it will always be listed with its direction or orientation—”BU” (base up), “BI” (base in, toward the nose), or “BO” (base out, toward the temple).

What frames should I get?

Prescription eyeglasses come in all kinds of shapes, sizes, and materials. Depending on your unique lifestyle and vision needs, it is important to choose the frames that will best assist you. Surely frames that suit a nearsighted astigmatism prescription might not always be the best choice for someone that is adjusting to a new progressive lens prescription.

At IVI Vision, all of our classic optical frames are handcrafted out of premium Italian cellulose acetate from Mazzucchelli 1849. As long as you have your glasses prescription, you have the option to add on lens prescription to all of our designer acetate optical frames.

IVI Vision optical frames

IVI provides anti-reflective lens coating and blue light filtering lenses for you to build your perfect pair of designer prescription eyeglasses. The half-rim Producer is a modern creation of the vintage Hollywood film style, the designer prescription eyeglass frame of choice for any occasion. Show off your confidence and personal taste with animal-print Prerogative, a fierce combination of retro style and innovative trends. Looking for something more low-key? Cosmopolis is the perfect blend of sophistication and nonconformity. With an extensive variety of shades, Cosmopolis is the one to complete your signature look. If a timeless style if more your cup of tea, the luxury metal frames Agent will take you from day to night, from behind the scenes to in the spotlight. Don’t compromise your vision nor your style. With a good understanding of your needs and preferences, let glasses enhance the quality of your life.

Interested in reading more about your lenses?

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