How Do You Read an Eyeglass Prescription?
Visiting your optician or optometrist is definitely worth your time. Stepping into their office, you will likely complete an eye exam and answer some basic questions about your eyesight. From there, your optician or optometrist may write you a prescription for a pair of eyeglasses. Upon first glance, reading an eyeglass prescription is a strange hodgepodge of numbers, letters, and symbols.
Even though it may take some adjustment, your new pair of prescription eyewear can change your life. You’ll not only be able to see more clearly, but you will have all the power in the world to create a new, exciting look. When looking to purchase your first pair of prescription glasses, however, you will need to provide your eyeglass prescription. Nevertheless, each character represents a significant amount of information about your eyes and how your glasses can help you see more clearly. Therefore, this article is designed to help you better understand what those characters in your eyeglass prescription actually represent.
Reading Your Eyeglass Prescription: What You Need to Know
Upon reading your eyeglass prescription, you will immediately notice that there are groups of characters arranged in a two-row table. We are going to go over all of these rows and letters, but to start, it is helpful to focus on the terms “OD” and “OS.” These two terms are easy to understand. OD stands for “oculus dexter,” which is a Latin term for the right eye. OS stands for “oculus sinister,” and as you can guess, that stands for the left eye.
Importantly, there is a separate prescription for each of your eyes. As you can see in the table, the remaining parameters in the table apply to both your right eye and left eye. The figures can be different for each eye.
Moving along the table, you will see a column titled “SPH.” It stands for a sphere. Sphere essentially means the amount of lens power that has been prescribed for your nearsightedness or farsightedness. If you are nearsighted, you will see a minus sign at the beginning of this figure. If you are farsighted, you will see a plus sign. This is easy enough, but what about that number after the plus or minus sign? The sphere is measured in diopters, which is the unit used to measure the focusing power of the lens your eye requires. For instance, if you have a sphere of -1.00, this means that you have a diopter of 1.00 for nearsightedness. A sphere of +3.00 means you have a diopter of 3.00 for farsightedness. The higher the number, the stronger your prescription needs to be to correct your farsightedness or nearsightedness.
From sphere, you will see cylinder (sometimes abbreviated as “CYL”). It is one of the factors necessary to correct astigmatism. Like a sphere, this can be a negative or positive number. Also like a sphere, the cylinder is measured in diopters. It measures the precise degree of astigmatism that you have. Simply put, the larger the number here, the more astigmatism that you have.
The cylinder is only half of the equation to correct astigmatism, however. You also need to take note of the axis. The axis is important because it reveals the orientation of astigmatism. This is a number that can be anywhere from 0 to 180. Once again, if you have astigmatism, you will see numbers in both the cylinder cell and axis cell (for both eyes). Between the cylinder and axis cells, you may also notice an “X” symbol. Ultimately, if you have astigmatism, there will be three numbers in your prescription. It is typically noted by the sphere x cylinder x-axis.
From the cylinder and axis, your prescription may or may not contain information in the “prism” cell. Prism, which is measured in prismatic diopter, is necessary when you need assistance with your eye alignment. There are three indicators that provide information about the base direction or thickest edge of the prism. Those indicators are base out (“BO”), base up (“BU), base in (“BI”) or base down (“BD”).
Finally, there is also a column for “add.” Essentially, add provides magnifying power for things like reading, bifocal, multifocal, and progressive lenses. This number ranges between +0.75 and +3.00 and it is likely the same for both of your eyes. If you need to add of lower than +0.75, you will likely be able to get it by speaking with your optometrist or optician.
This is the simple table that you will see in a standard prescription for eyeglasses. Below that table, there are two additional cells. The first is labeled “PD.” PD stands for pupillary distance. This is the distance between the center of one pupil to the center of your other pupil. Ultimately, PD helps you with your vision because it shows where the optical center of your lenses should be placed. The final box that you will see states “indication or contraindication.” Here, your eye doctor would write additional notes about treatments that you should potentially avoid.
The above is how to read the general eyeglass prescription that your optician or optometrist would complete during your visit. All of these figures are combined into one line for both of your eyes. As just one basic example, you may see an eyeglass prescription of OD -2.00 -0.75 x 90 + 1.00 add 0.5 p.d. BU. OD stands for your right eye and -2.00 is the sphere. -0.75 is the cylinder and the cylinder has its axis at 90 degrees. 1.00 is the added power in this prescription. Finally, the prescription contains a prismatic diopter of 0.5 and the prism is base up. This is a simple example, but it goes to show how all of this information is represented in one line of text.
Understanding Your Eyeglass Prescription
Upon first glance, reading your eyeglass prescription can be confusing and difficult to understand. But having said this, by having a basic understanding of these abbreviations, it is easier to tell how your eyeglasses are helping you see more clearly. Each part of your prescription is playing a certain role in improving your eyesight. This is why it is important that each part of your prescription is accurate.
If you suspect that your prescription is wrong, give it a few weeks. It may take some time for your eyes to get adjusted to your new prescription. That said, if you are continuing to experience blurry vision or other symptoms like nausea or headaches, it is worth making another trip to your optometrist or optician. He or she will be able to better diagnose what is actually going on.
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