Knowing how to read glasses prescription is essential! If, you just had an eye exam and your ophthalmologist gave you a prescription for glasses. He or she may mention that you are near-sighted or far-sighted, or that you have astigmatism. Although you may know the condition of your eyesight, it is quite another matter to determine this from the prescription. You may be confused. What do all these numbers on the prescription for glasses mean? Those abbreviations on the prescription of glasses, such as OD, OS, SPH, CYL, Axis, Prism, PD and ADD. What do these mean? This article will help you to read and understand the prescription of glasses so that you can avoid misrepresentation when buying new glasses online, and it can also be effective in discussing with the optician. So, I have made a simple guide on how to read prescriptions for glasses, let’s find out now！

The meaning of OD and OS

The first step in understanding the prescription of glasses is to understand the meaning of "OD" and "OS", which are the abbreviations of "oculus dexter" and "oculus sinister", and are Latin for "right eye" and "left eye". There may also be a column labeled "OU" in your prescription for glasses. This is the abbreviation of the Latin "oculus uterque", which means " both eyes".

Although these abbreviated Latin words are often used in prescriptions for glasses, contact lenses and ophthalmic drugs, some doctors and clinics have chosen to use modern prescription glasses and use RE (right eye) and LE (left eye) instead of OD and OS.

In your prescription for glasses, the right eye (OD) information precedes the left eye (OS) information. Ophthalmologists write prescriptions in this way because when they face you, they will habitually start recording from the direction of their left hand to the right hand, which is corresponds to your right eye first, and then to the left eye.

Other parts of the glasses prescription

Your prescription for glasses also contains other terms and abbreviations. These include:

Sphere (SPH). The numbers in this section can correct myopia and hyperopia. For single vision prescriptions, if the number displayed under this heading has a minus sign (-), it means you are nearsighted. If it has a plus sign (+), it means you are farsighted (presbyopia). It is usually written in quarter diopter (0.25) increments.

Cylinder (CYL). This represents the astigmatic lens. If there is nothing in this column, the astigmatism you need to correct is small or not. The numbers in the column can be preceded by a minus sign (used to correct for myopic astigmatism) or plus sign (used for hyperopic astigmatism).

(Axis). If you have astigmatism, the axis number will also be included. This number indicates the angle of a lens that should not have cylindrical power to correct your astigmatism. This value follows the cylinder degree and starts with "x" when writing freehand. Use a number between 1 and 180 to define the axis. The number 90 corresponds to the vertical meridian of the eye, and the number 180 corresponds to the horizontal meridian.

(Prism) tells you the prism power required to correct eye alignment problems. Of course, only a small number of prescription glasses have this. Prism correction is on the prescription of that small group of spectacle wearers. One more thing: your prescription medicine may also have a prism value, measured in prism diopters. Just like the pupillary distance, the prism diopter can be abbreviated as PD. Generally speaking, your prescription will indicate Prism or use a triangle for shorthand to avoid confusion. However, if the PD value is between 0 and 1, it is likely to be a prism diopter value. The higher value is a measurement in millimeters and represents your pupil distance. We can fill in these contents for single vision (non-multifocal) prescriptions not exceeding 5.00 in any basic direction (basically upward, basic downward, basically inward or basically outward).

PD (Pupillary Distance) The distance from the center of the right eye to the center of the bridge of the nose, and the center of the left eye to the center of the bridge of the nose. In short, the interpupillary distance is the distance between the pupils of the eyes. The average adult PD is between 54 and 74 mm. For children, it is approximately between 43 and 58 mm.

(Add). Tell us the second prescription for multifocal glasses. This is an additional magnification applied to the bottom of a multifocal lens to correct presbyopia. The number that appears in this part of the prescription is always a "plus sign," even if there is no plus sign in front of it. Usually, it ranges from +0.75 to +3.00 D, and the refractive power of both eyes is the same.

Additional Information

Your ophthalmologist may also write specific lens recommendations (such as anti-reflective coatings, photochromic lenses and/or progressive lenses) on your glasses prescription to provide you with the most comfortable vision correction possible.

Still confused? Okay, let's clean it up with an example.

Examples of glasses prescription

The myopia prescription will display a number with a minus sign (-) in the "sphere" box. This means that your lenses will be corrected to improve the invisible distance.

Prescriptions for people with hyperopia problems will display numbers with a plus sign (+) in the "sphere" box. In layman's terms, this means that your lenses are reading glasses.

If you have astigmatism, there will be a number in the "Cylindrical" column of the prescription indicating the lens power required to correct the astigmatism. When correcting for astigmatism, there will also be a number in the "Axis" column.

Multifocal prescriptions will contain ADD values, sometimes marked as NV. This represents the strength required for the near prescription in the lens.

How often should you get an eye exam?

 If you don’t have any medical issues that affect your vision, you should have a comprehensive eye exam every one to two years.

Can eyeglass prescriptions be used to buy contact lenses?

Here are some one more small tips from ANRRI:

The prescriptions for glasses and contact lenses are different. The prescription for glasses is only applicable to the purchase of glasses. It cannot summarize the degree of contact lens. An accurate contact lens prescription can only be written after the contact lens has been fitted and the prescribing doctor has assessed your eye's response to the glasses and the overall response to wearing contact lenses. But, maybe you already have a prescription for glasses, how to simply determine your prescription for contact lenses? It's simple. Generally speaking, the prescription for contact lenses is 0.25 degrees lower than the prescription for glasses because the contact lenses fit the naked eye.