How to Read Your Prescription

Understanding your eyeglass prescription may seem confusing at first, but once you know what each number means, it becomes much easier. Whether you’re getting standard glasses or large-size frames, knowing how to read your prescription ensures you get the right lenses for your vision needs.

1. Know the Main Components

Most prescriptions include several key abbreviations:

• OD (Oculus Dexter) – Right eye

• OS (Oculus Sinister) – Left eye

• SPH (Sphere) – Indicates nearsightedness (-) or farsightedness (+)

• CYL (Cylinder) – Measures astigmatism, the irregular curvature of the eye

• AXIS – Degree of astigmatism (0–180)

• ADD – Added magnification for multifocal lenses

• PD (Pupillary Distance) – The distance between the centers of your pupils, used to properly align the lenses with your eyes.

• Prism – Used to correct eye alignment issues such as double vision by slightly shifting the image position so both eyes can work together comfortably.

Note: Some prescriptions include PD, while others may not. If your prescription does not list PD, you may need to ask your optometrist for it or measure it separately when ordering glasses online.

2. Understanding Pupillary Distance (PD)

PD is the distance between the centers of your pupils. It ensures the lenses are aligned properly with your eyes. This is especially important for larger frames, as the wrong PD can cause strain or blurred vision.

There are two types of PD measurements:

• Single PD – One number that measures the total distance between both pupils (for example, 64 mm).

• Dual PD – Two numbers that measure the distance from the center of the nose to each pupil separately, such as 32mm/32mm.

Dual PD is often more precise, especially for higher prescriptions or progressive lenses.

If your glasses prescription doesn't include your PD, we can show you how to measure it by yourself at home.

1. Fold the ruler and flip it to the side labeled “Using a Mirror.”

2. Stand about 8 inches (20 cm) in front of a mirror.

3. Hold the ruler horizontally across your eyes and align the 0 mark with the center of your left pupil. For better stability, you can lightly rest the ruler against your forehead.

4. Close or cover your left eye, and look straight ahead with your right eye.

5. The number that lines up with the center of your right pupil is your pupillary distance (PD).
   

3. Single Vision vs. Multifocal Lenses

Single Vision: Corrects either distance or reading vision. Simple, thin, and lightweight—perfect for large frames.

Bifocal Lenses: Have two distinct zones for distance and near vision, separated by a visible line. Easy to fit in large frames while keeping the line placement comfortable.

Progressive Lenses: Offer a smooth transition from distance to near vision with no visible line. Ideal for large frames, combining style and full-range vision correction.

This tells your optician how to craft lenses that correct your vision accurately.

4. Tips for Ordering Glasses

1. Always provide your latest prescription with PD.

2. Double-check the numbers before placing an order.

3. Consider frame size—oversized or wide frames work well for those with bigger faces, providing both comfort and style.

4. If you’re unsure, consult your optometrist to verify your prescription details.

Now that you’re a pro at reading your prescription, it’s time to find a pair that actually fits. At SizeGlasses, we specialize in frames that offer the extra width you need without compromising on optical precision. Explore our collection of large-size eyeglasses and sunglasses designed specifically for bigger heads and wider faces.