Complete Eyeglass Lens & Prescription Guide

Choosing the right lenses can feel confusing, especially with different lens indexes, coatings, and prescription measurements. This guide will help you understand your eyeglass prescription, measure your pupillary distance, and choose the best lens option for your vision needs.

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How to Read Your Eyeglass Prescription

Your prescription contains important measurements that tell us how to create your lenses. Below is an example of a typical eyeglass prescription:

1. OD (Right Eye) and OS (Left Eye)

Eyeglass prescriptions usually use OD for the right eye and OS for the left eye. It is normal for each eye to have different measurements.

2. Sphere (SPH)

Sphere indicates the main lens power needed to correct your vision.

• Negative (-) values correct nearsightedness, or difficulty seeing distant objects clearly.
• Positive (+) values correct farsightedness, which can affect near or distance vision depending on the individual.

3. Cylinder (CYL)

Cylinder measures the amount of correction needed for astigmatism. If your prescription includes a CYL value, your lenses require additional correction to provide clear vision.

4. Axis

Axis works together with the CYL measurement and describes the orientation of the astigmatism correction. It is measured from 1 to 180 degrees.

5. ADD (Reading Addition)

ADD indicates additional magnifying power prescribed for reading and close-up vision. It is commonly included on prescriptions for progressive, bifocal, or other multifocal lenses and helps correct presbyopia.

6. Pupillary Distance (PD)

Pupillary distance, commonly called PD, is the distance between the centers of your pupils. It is measured in millimeters and is used to position the optical center of each lens correctly in front of your eyes.

An accurate PD measurement is important for clear and comfortable vision. Your PD may appear on your prescription, although some eye doctors record it separately because it is technically a fitting measurement rather than part of the prescription itself.

Single PD vs. Dual PD

Your PD may be written in one of two ways:

• Single PD: One number representing the total distance between both pupils, such as 63 mm.
• Dual PD: Two numbers showing the distance from the center of your nose to each pupil, such as 31 mm / 32 mm. The first number normally represents the right eye and the second represents the left eye.

A dual PD may provide more precise lens positioning when the face is not perfectly symmetrical. When ordering, enter your PD exactly as it appears on your prescription or measurement.

How to Measure Your Pupillary Distance

For the most accurate result, ask your eye doctor or local optician to measure your PD. If your prescription does not include it, you can also estimate your distance PD at home using a millimeter ruler and a mirror.

How to Measure Your Own PD in a Mirror

1. Stand approximately 8 inches, or about 20 centimeters, away from a mirror in a well-lit room.
2. Hold a millimeter ruler horizontally against your eyebrows or just above your eyes. Keep the ruler level and avoid bending it.
3. Close your right eye and align the ruler's 0 mm mark with the center of your left pupil.
4. Without moving the ruler, open your right eye and close your left eye.
5. Look straight ahead and read the millimeter measurement that lines up with the center of your right pupil.
6. The resulting number is your single distance PD.

For example, if the center of your right pupil lines up with 63 mm, your single PD is 63 mm.

How to Have Someone Else Measure Your PD

1. Sit or stand directly in front of the person measuring you at approximately the same eye level.
2. Look straight ahead at a distant object behind the person rather than looking directly at their face.
3. Have the person hold a millimeter ruler horizontally across the bridge of your nose.
4. Align the ruler's 0 mm mark with the center of one pupil.
5. Measure across to the center of the other pupil without tilting or moving the ruler.
6. Record the measurement in millimeters and repeat the process to confirm the result.

How to Measure Dual PD

To measure dual PD, place the ruler's 0 mm mark at the center of the bridge of your nose. Measure from the center of your nose to the center of your right pupil, and then repeat for your left pupil.

Record the measurements separately, with the right-eye measurement first. For example:

Right PD: 31 mm | Left PD: 32 mm

Tips for an Accurate PD Measurement

• Use a ruler that clearly displays millimeters rather than inches.
• Keep your head upright and look straight ahead.
• Keep the ruler level and close to your face.
• Measure your PD at least three times and compare the results.
• If the measurements differ, repeat the process rather than averaging significantly different results.
• Ask another person to verify the measurement when possible.
• Do not use a PD measurement taken from an old pair of glasses unless it was provided by an eye care professional.

Distance PD is generally used for distance and progressive glasses. Reading-only glasses may require a different near PD, so use the measurement recommended by your eye doctor when ordering reading lenses.

If you are unsure about your measurement, contact us before placing your order. We can review the information you have and help you determine what is still needed.

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Do I Need Single Vision or Progressive Lenses?

Your prescription can help indicate which lens type may have been prescribed, but an ADD value does not automatically mean that progressive lenses are required. Your eye doctor may recommend progressive, bifocal, reading, occupational, or another multifocal lens design.

Single Vision Lenses

Single vision lenses provide one prescription power throughout the lens. Depending on your prescription, they may be made for:

• Distance vision
• Computer or intermediate vision
• Reading or near vision

If your prescription does not include an ADD value, you will commonly need single vision lenses. However, you should follow the lens type recommended by your prescribing doctor.

Progressive Lenses

Progressive lenses provide a gradual transition between distance, intermediate, and near vision without visible dividing lines. They are commonly prescribed for people who need help seeing clearly at multiple distances.

If your prescription includes an ADD value, it means additional near-vision power has been prescribed. Confirm whether your doctor recommends progressive lenses, bifocals, reading glasses, or another multifocal option before ordering.

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Choosing the Right Lens Index for Your Prescription

Lens index refers to how efficiently a lens material bends light. A higher index allows the same prescription correction to be made with less material, helping create thinner and often lighter lenses.

Use the chart below as a general recommendation. Your ideal lens choice may also depend on your frame size, frame shape, full prescription, and personal preferences.

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Understanding Different Lens Index Options

1.56 Standard Index Lenses

1.56 lenses are a practical choice for light prescriptions up to approximately ±2.00. They provide clear vision and are an affordable option for everyday glasses.

1.61 High-Index Lenses

1.61 high-index lenses are recommended for many prescriptions around ±2.00 to ±5.00. They provide a thinner and lighter option compared with standard lenses.

1.67 High-Index Lenses

1.67 lenses are designed for stronger prescriptions around ±5.00 to ±7.00. They help reduce lens thickness and can provide a cleaner appearance in suitable frames.

1.74 Ultra High-Index Lenses

1.74 lenses are our thinnest lens option and are generally recommended for prescriptions around ±7.00 and above. They are ideal for customers who want maximum lens thinning for a strong prescription.

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Other Factors That Affect Lens Thickness

• Frame size: Larger frames generally require more lens material and may result in thicker lenses.
• Frame shape: Smaller, well-centered frames can help reduce visible edge thickness.
• Frame style: Full-rim frames may conceal lens edges better than rimless or semi-rimless designs.
• Astigmatism: Higher CYL values and axis placement can affect lens thickness.
• Pupillary distance: How your pupils align within the frame can affect the amount of lens material required.
• Prescription strength: Stronger prescriptions generally benefit more from high-index materials.

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Popular Lens Upgrades

In addition to choosing the right lens index, you can customize your glasses with additional lens features:

• Anti-Reflective Coating: Helps reduce reflections and improve the appearance and clarity of your lenses.
• Blue Light Filtering: Filters a portion of the blue light emitted by digital screens and other light sources.
• Photochromic Lenses: Darken in response to ultraviolet light outdoors and return to a clearer state indoors.
• Polarized Lenses: Help reduce reflected glare from surfaces such as roads, water, and snow.

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Need Help Choosing Your Lenses?

Every prescription is different. If you are unsure which lens index or lens type is right for you, our optical team is happy to help.

Contact Youtop Optical before ordering, and we can recommend an option based on your prescription, selected frame, and lifestyle.