If you are one of the 166 million people in the U.S. who wear glasses, you know how important the right prescription is. From glasses prescriptions to contact lens prescriptions, accuracy is paramount when dealing with eye correction.
Only a skilled optometrist can provide an accurate prescription for your glasses. But, doing so isn't always easy. There are several important steps eye doctors must take when prescribing your current glasses.
Read on to learn more about how your eye doctor can provide your prescription information using only your current lenses and a few handy tools.
Key takeaways:
- Opticians can tell your glasses prescription through a process called "reading".
- Using a lensometer can help doctors take proper measurements from your glasses, helping them to "reverse engineer" your prescription.
- Indicators like spherical number, cylinder number, AXIS, ADD, PRISM, BASE, and pupillary distance can all help you determine your glasses prescription.
- Regular eye exams can help your eye doctor prescribe a valid prescription for your new glasses purchase.
See Related: What Are Single-Vision Glasses?
Can an optician tell your prescription from your glasses?
The short answer is: yes. Optometrists can determine your glasses prescription through a sort of “reverse-engineering”. Through a process called “reading” your prescription, they are able to determine both the strength and the correction of your glasses lenses.
However, this reading alone does not allow them to provide you with a legally valid prescription. You may still need a new eye exam in order for your optician to generate a new, valid prescription for your new glasses.
How eye doctors determine a glasses prescription from your current pair
In addition to reading straight from your glasses, doctors have several tools to help them measure various parts of the eye.
Doctors may take the following steps to determine your prescription:
Use a lensometer: To read your prescription using your current pair of glasses, an optometrist will use a machine called a lensometer, which measures several specifications.
Measure lens properties: Using the lensometer, your optometrist will read the sphere, cylinder, and axis. They may also identify lens coatings and special instructions, as well as determine the back vertex distance (BVD) and pupillary distance (PD).
The following indicators can help your optician read prescriptions for your eyeglasses:
- "+" and "-"
- Spherical number
- Cylinder number and AXIS
- ADD
- PRISM and BASE
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Pupillary distance (PD)
‘+’ and ‘-‘ signs
A plus sign or minus sign can signify whether a person has farsightedness (hyperopia) or nearsightedness (myopia). A ‘+’ sign means the glasses wearer has farsightedness, while a ‘-' sign means they have nearsightedness.
Spherical number
Your glasses’ spherical number, represented by the letters SPH, can tell how strong the lenses need to be in order to correct a person’s vision. This information is vital for correcting refractive errors and helping restore clear vision across different distances.
A person may also notice an infinity sign or “plano (Pl)” on their prescription, signifying that a person is emmetropic. This is the term used to represent that a person is neither farsighted nor nearsighted. They may, however, still have astigmatism or presbyopia.
Cylinder number and AXIS
Your glasses’ cylinder number, also known as the CYL, tells whether a person has astigmatism. Cylinder numbers can be positive or negative.
The AXIS is represented by a number between 1 and 180, which shows the position of the astigmatism. If a person does not have astigmatism, a prescriber may leave the cylinder number field blank or write “sphere” in its place.
ADD
The ADD field on a prescription is used for those who require bifocals, varifocals, or progressive lenses.
PRISM and BASE
PRISM and BASE relate to muscle imbalance in the eyes. A PRISM number is often represented in fractions, while the base is represented by abbreviations like BO (base out), BI (base in), BD (base down), and BU (base up).
Pupillary distance (PD)
Pupillary distance is the distance between the pupil center points. This figure is important when attempting to purchase eyeglasses online, as the PD helps ensure the glasses fit properly and the lenses and eyes are centered.
Bonus: Glasses Measurements - How to Know Your Frames Size
How to find your contact lens prescription
Finding your contact lens prescription is similar to the process of finding your glasses prescription.
First, you’ll need to schedule an eye exam with an optometrist or ophthalmologist who can evaluate your eyes and determine your prescription. This prescription will include:
- Power (sphere or diopter)
- Cylinder (if astigmatism is present)
- Axis (if astigmatism is present)
- Diameter (size of the contact lens)
- Base curve (shape of the contact lens)
Once you obtain a prescription, be sure to keep it in a safe place so that it can be easily accessed the next time you purchase new contacts.
Why regular eye exams are important
Regular eye exams are important for healthy eyes. If you are having trouble with your vision, obtaining the correct prescription is only possible through a comprehensive eye exam with a skilled professional.
Scheduling appointments for regular eye examinations can help address any vision changes and provide the answers you need to prevent eye disease. Whether you need an eyeglass prescription, prescription sunglasses, or have other prescription needs, a vision test is essential for guiding your eye doctor through your personalized care.
Oculus Eye Care carries a wide selection of luxury prescription glasses to help people all over the world see more clearly. Schedule a visit with one of Oculus' trained eye specialists to get tested and fitted for your perfect pair.
Conclusion
Knowledge is power when it comes to your vision. Knowing your correct eyeglass prescription or contact lens prescription is the first step toward finding the right pair of prescription glasses to help you improve your eyesight.
Your eye doctor is the best person to help shed light on your eye health. By reading your prescription, they can ensure you get the very best shot at clear vision.
Keep Reading: Why Are My Clear Glasses Frames Turning Yellow?
Frequently Asked Questions (FAQ)
Can I order eyeglasses without knowing my PD?
No, you can’t order prescription glasses without knowing your pupillary distance (PD) measurement. This figure is crucial for lens alignment, clear vision, and preventing eye strain.
Although some retailers may use an average PD, the best way to obtain an accurate prescription is to have your eye doctor take proper measurements using a ruler and a mirror. You may also use an online PD tool.
What should I avoid when buying prescription glasses online?
When buying prescription glasses online, you should avoid unverified retailers, using inaccurate measurements, or ordering with an outdated prescription. Also, pay close attention to materials and skip enhancements like UV protection or anti-glare.
What happens if I order glasses with the wrong PD?
Wearing eyeglasses with the wrong pupillary distance (PD) should be avoided, as this can lead to uncomfortable symptoms like headaches, eye strain, blurred vision, or dizziness. In some cases, the wrong PD can make your existing vision problems worse.
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