Understanding Your Eyeglass Prescription: A Comprehensive Guide
Receiving an eyeglass prescription can sometimes feel like being handed a cryptic message. All those abbreviations and numbers might seem confusing, but they hold the key to understanding your vision correction needs. This comprehensive guide will demystify the jargon and empower you to interpret your prescription accurately, ensuring you get the right eyewear for optimal vision.
Decoding the Abbreviations: OD, OS, OU
These abbreviations are Latin terms that specify which eye your prescription refers to:
OD (Oculus Dexter): This refers to your right eye.
OS (Oculus Sinister): This refers to your left eye.
OU (Oculus Uterque): This refers to both eyes.
You'll typically find these abbreviations at the top of your prescription, clearly indicating which measurements apply to each eye. Sometimes, the prescription will be written in columns, with OD on the left and OS on the right. If the values are the same for both eyes, the prescription might only list one set of values under OU.
Understanding Sphere (SPH)
The Sphere (SPH) value indicates the amount of lens power, measured in dioptres (D), needed to correct nearsightedness (myopia) or farsightedness (hyperopia).
Minus (-) sign: A minus sign before the number indicates nearsightedness. The higher the number, the stronger the correction needed. For example, -2.00 D indicates a stronger correction than -1.00 D.
Plus (+) sign: A plus sign before the number indicates farsightedness. The higher the number, the stronger the correction needed. For example, +3.00 D indicates a stronger correction than +1.50 D.
Think of the sphere value as the primary power needed to focus light correctly onto your retina. If you see a "PL" or " Plano" in the SPH box, it means you have no nearsightedness or farsightedness correction in that eye.
Understanding Cylinder (CYL) and Axis
The Cylinder (CYL) and Axis values correct for astigmatism. Astigmatism occurs when the cornea (the clear front surface of the eye) is not perfectly spherical, causing blurred or distorted vision at all distances.
Cylinder (CYL): This value indicates the amount of lens power, measured in dioptres (D), needed to correct the astigmatism. Like the sphere value, it can be preceded by a minus (-) or plus (+) sign. A minus sign is more common. The higher the number (regardless of the sign), the greater the degree of astigmatism.
Axis: This value indicates the orientation of the astigmatism correction. It's measured in degrees, ranging from 1 to 180. The axis specifies the angle at which the cylinder power should be applied to correct the distortion caused by the astigmatism.
It's crucial to have both the CYL and Axis values correct for effective astigmatism correction. If the CYL value is blank, it means you have no measurable astigmatism in that eye. For example, a prescription might read: OD: SPH -1.00, CYL -0.50, Axis 90. This means the right eye has a nearsightedness correction of -1.00 dioptres and an astigmatism correction of -0.50 dioptres at an axis of 90 degrees.
Understanding Add and Prism
These values are less common but essential for certain vision conditions.
Add: This value is the added magnifying power needed to correct presbyopia, the age-related loss of near focusing ability. It's typically found on prescriptions for bifocals or progressive lenses. The Add value is always a positive (+) number, and it's usually the same for both eyes. It represents the additional power needed for reading and close-up tasks, added to the distance correction specified in the SPH value. For example, if your prescription shows an Add of +2.00, it means you need an additional +2.00 dioptres of power for near vision.
- Prism: This value corrects for eye alignment problems (strabismus) that can cause double vision. It indicates the amount and direction of prism needed to realign the images seen by each eye. Prism is measured in prism dioptres (PD) and is always accompanied by a direction, such as BU (base up), BD (base down), BI (base in), or BO (base out). For example, a prescription might read: OD: 1.0 PD BU, meaning the right eye requires 1.0 prism dioptres with the base up. If you need prism correction, it's vital to get your eyeglasses made accurately to ensure proper eye alignment and comfortable vision.
Pupillary Distance (PD) Explained
Pupillary Distance (PD) is the distance between the centres of your pupils, measured in millimetres (mm). This measurement is crucial for ensuring that the lenses in your eyeglasses are correctly centred in front of your pupils. An accurate PD ensures that you are looking through the optimal part of the lens, providing the clearest and most comfortable vision. Your PD might be written as a single number (e.g., 62 mm) or as two numbers (e.g., 31/31 mm), indicating the distance from the centre of your nose to each pupil.
Your optometrist or ophthalmologist will usually measure your PD during your eye exam. If your PD isn't included on your prescription, you can ask them to provide it. You can also measure your PD yourself or have it measured at Glassesonline when you purchase your glasses. Accurate PD measurement is essential for optimal vision correction.
How to Get Your Prescription
Your eyeglass prescription is typically provided to you by your optometrist or ophthalmologist after a comprehensive eye exam. During the exam, they will assess your vision and determine the appropriate lens power needed to correct any refractive errors. You are legally entitled to a copy of your prescription after the exam. Keep your prescription in a safe place, as you'll need it when purchasing eyeglasses or contact lenses.
Your prescription is valid for a specific period, usually one to two years, depending on local regulations and your individual eye health. It's important to have regular eye exams to monitor your vision and ensure your prescription is up-to-date. If you notice any changes in your vision, such as blurred vision, double vision, or eye strain, schedule an appointment with your eye care professional as soon as possible. Remember that an eyeglass prescription is different from a contact lens prescription. A contact lens prescription includes additional information, such as the base curve and diameter of the lens, which are necessary for a proper fit. You can learn more about Glassesonline and the importance of regular eye exams. For more information, you can also check frequently asked questions about eye prescriptions.
Understanding your eyeglass prescription empowers you to make informed decisions about your vision correction. By understanding the abbreviations and numbers, you can ensure that you get the right eyewear for your specific needs. If you have any questions or concerns about your prescription, don't hesitate to ask your eye care professional for clarification. They are the best resource for providing personalised advice and ensuring your vision is as clear and comfortable as possible. When choosing a provider, consider what Glassesonline offers and how it aligns with your needs.