Understanding your eyeglasses prescription can feel daunting due to the numbers and specific terms involved (some of which are in Latin!). However, breaking it down can help you better understand your vision needs and what your optometrist is treating. Whether you're new to glasses or seeking clarity on your pre-existing prescription, this guide will hopefully simplify the various elements found on your eyeglasses prescription, so you can feel confident when discussing your eye care provider.
What is a Glasses Prescription?
A glasses prescription is a printed document outlining the vision correction you need, including specific measurements that assist your optometrist, optician, or optometric assistant in crafting lenses for your eyes. Typically provided after a comprehensive eye exam, it details adjustments necessary for optimal clarity.
Understanding the Key Components
When reading your glasses prescription, you will encounter key abbreviations and measurements. Familiarizing yourself with these terms is essential for accurately interpreting your prescription.
OD - Oculus Dexter
OD or Oculus Dexter is the Latin term that translates to “right eye". Everything listed under this abbreviation in your prescription pertains specifically to the correction needed in your right eye.
OS - Oculus Sinister
OS or Oculus Sinister is the Latin term that translates to “left eye". Everything listed under this abbreviation in your prescription pertains specifically to the correction needed in your left eye.
Sphere (SPH)
The Sphere (SPH) value indicates the lens power needed to correct your vision, measured in diopters (D). A positive number suggests you are farsighted (called hyperopic), while a negative number indicates nearsightedness (called myopic).
For example, if your SPH reads -2.00, you have a prescription strength of 2.0 diopters, marking mild nearsightedness. Conversely, a SPH of +1.50 shows a prescription for mild farsightedness.
Cylinder (CYL)
The Cylinder (CYL) value helps measure astigmatism, a common imperfection in the eye's curvature. Like the Sphere, the Cylinder is measured in diopters. If your prescription has a CYL value, it will specify the power and sign (positive or negative). Optometrists (Doctors of Optometry) typically write cylinder in negative form and Ophthalmologists (Medical Physicians) write cylinder in positive form.
For instance, a prescription showing a CYL of -1.25 means you have moderate astigmatism, requiring that level of correction for proper vision.
Axis
The Axis complements the Cylinder value, indicating the orientation of your astigmatism, represented in degrees from 1 to 180. This measurement directs lens manufacturers on where to position the cylindrical component within the lens.
For example, a prescription stating an Axis of 90 degrees signifies that the astigmatism correction should be placed vertically to achieve clarity.
Addition (ADD)
The Addition (ADD) value indicates the extra magnifying power needed for the lower part of bifocal or progressive lenses. This is particularly important for those who require reading glasses or multifocal lenses.
A typical ADD value is +2.00, indicating an additional power of 2 diopters is required.
Pupillary Distance (PD)
Pupillary Distance (PD) measures the distance between your pupils, essential for correct lens fitting. Proper alignment enhances comfort and clarity.
Your PD may appear as a single number (monocular) or two numbers (binocular), like 65mm or 32.5/32.5. For example, a PD of 65mm is common for many adults, ensuring lenses sit perfectly in front of your pupils.
Prism
There may be a field for prism on the right side. This is a special type of correction built into the lens for some people with double vision (seeing two separate images of the same object). The prism fuses the two images together so only one image is seen.
How to Read Your Prescription
Now that you understand the components, putting it all together is fairly straightforward. Here’s an example of what a prescription might look like:
In this case, the right eye has a sphere power of +0.25 with -1.25 for astigmatism at a 148-degree axis. The left eye has a sphere power of +1.50 and -1.00 for astigmatism at an 130-degree angle. This person also requires prism in his glasses to help keep his eyes aligned.
Common Prescription Terms
Your prescription may include additional terms that provide insight into your vision needs:
Single Vision: This type of lens has one prescription, suitable for either distance or near vision.
Multifocal: Multifocal prescriptions have two distinct prescription powers, generally for distance and near vision, and can be used to create a multitude of optical devices such as single vision distance, readers, bifocals, progressives and office style lenses.
Why is This Important?
Understanding your glasses prescription goes beyond knowing numbers. It significantly affects your daily life and well-being. With the right prescription, you are likely to experience less eye strain, sharper clarity, and a better quality of life. Research indicates that 60% of individuals experience discomfort in their day-to-day tasks if their prescription is incorrect. If you experience discomfort or headaches while wearing your glasses, consult your eye care professional to reassess your prescription.
What about contact lenses?
Since contact lenses rest directly on the eye, their prescription differs from that of eyeglasses. A contact lens prescription contains measurements unique to the size and brand of your lenses. Prior to obtaining a prescription, you must undergo a "contact lens fitting" to determine if they are suitable for you.
Wrapping It All Up
Your eyes are your windows to the world, and understanding your glasses prescription is a vital first step in protecting them. If ever confused about your prescription, reach out to your optometrist for clarification. They are there to support you in meeting your vision needs successfully.
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