The Complete Guide to Buying Glasses Online: Getting Your PD Right

Buying Glasses Online PD Guide

Last updated: January 2025 | Reading time: 12 minutes

Buying glasses online can save you 50-80% compared to traditional optical shops. The frames are the same brands. The lenses are comparable quality. The only real difference? You're responsible for providing your own measurements.

That's where many online glasses purchases go wrong—not because online retailers are inferior, but because customers provide incorrect information. Chief among these measurements: pupillary distance.

This guide walks you through everything you need to successfully order glasses online, with special focus on getting PD right.

Why Online Glasses Are Cheaper

Before diving into how-to, it helps to understand why the price gap exists—so you can appreciate both the opportunity and the responsibility.

Traditional optical retail involves:

Prime retail space (high rent)
Sales staff (commissions, benefits)
On-site inventory (capital tied up in frames)
Same-day service expectations (premium pricing)

Online retailers eliminate most of these costs:

Warehouse locations instead of retail space
Minimal sales staff (automated systems)
Just-in-time inventory or virtual try-on
Shipping time instead of instant gratification

The savings are real. A frame that costs $400 at a mall optical shop might be $100-150 online with identical lenses. That's not a marketing gimmick—it's the economics of different business models.

What Online Retailers Need From You

When you order in-person, staff gather all necessary information through interaction. When you order online, you provide everything via forms. Typical requirements:

Your Prescription

This comes from your eye doctor and includes:

Sphere (SPH): The main correction power
Cylinder (CYL) and Axis: Astigmatism correction
Add: Additional power for reading (if applicable)

Prescriptions expire (typically 1-2 years depending on state law). You'll need a current one.

Your Pupillary Distance

This is where you come in. Online retailers can't measure your face through a screen. They need you to provide PD, which determines where optical centers are positioned in your lenses.

Frame Selection

You choose frames from their catalog. Some sites offer virtual try-on using your phone camera.

Lens Options

You select coatings (anti-reflective, blue light filtering), materials (standard plastic, high-index, polycarbonate), and lens types (single vision, progressive).

Getting Your PD: The Critical Step

Your prescription ensures the right correction. Your PD ensures it's positioned correctly. Both matter.

Option 1: Ask Your Eye Doctor

When you get your exam, request your PD. Some practices provide it automatically; others require asking.

If they measure but won't give you the number, that's a separate issue (addressed elsewhere). But many practices will simply include it if you ask at the time of exam.

Option 2: Use Your Previous Glasses

If you have glasses that work well, their optical centers reveal the PD used. Any optical shop can measure this for you (often free), or you can attempt it yourself by identifying the optical center of each lens and measuring between them.

Caveat: This assumes your previous glasses were made correctly.

Option 3: Self-Measure

Various techniques exist for self-measurement:

Mirror and ruler method
Photo method with reference object
Online tools and apps

The key is accuracy. A wrong number defeats the entire purpose of careful online shopping.

Option 4: Visit an Optical Shop Just for PD

Some people get exams from their ophthalmologist, then visit Costco, Walmart Vision, or a local optician solely for PD measurement. This is perfectly reasonable—you're purchasing a specific service.

Entering Your PD: Common Pitfalls

When placing your online order, you'll enter PD into a form. Mistakes at this stage ruin otherwise good measurements.

Single vs. Dual PD

Some sites ask for single (binocular) PD: one number like 63mm. Some sites ask for dual (monocular) PD: two numbers like 31/32mm. Some sites offer both options.

Know which format you're providing and enter appropriately. If you have monocular PD but the site only accepts single, add your two numbers together (31 + 32 = 63).

Right/Left Order

When entering monocular PD, be clear about which number is which. Standard convention is OD (right eye) first, OS (left eye) second, but verify what the specific site expects.

Distance vs. Near PD

Most sites assume distance PD. If you're ordering reading glasses, you may need to calculate near PD yourself (distance PD minus 3-4mm) and enter that.

Check if the site automatically adjusts for reading glasses—some do, some don't.

Verification Before Submission

Before clicking "order," verify:

PD numbers are correct (not transposed, not converted wrong)
Format matches what the site expects
The PD field actually populated (some forms can glitch)

Matching PD to Frames

Frame selection affects how well your PD is accommodated:

Frame PD

Every frame has a natural PD it works best with—roughly the distance between the geometric centers of the two lens openings. This is related to frame width and bridge width.

If your PD is 58mm and you select frames designed for 68mm PD, your lenses will be positioned very differently than ideal. The optical centers will be decentered significantly, which:

Works poorly for high prescriptions
Can affect lens thickness and appearance
May cause fitting issues

Finding Compatible Frames

Some online retailers show "recommended PD range" for each frame. Others let you filter by PD compatibility. If neither is available, look at the frame measurements:

Frame measurements are often written as: 52-18-140

52 = Lens width (mm)
18 = Bridge width (mm)
140 = Temple length (mm)

Add lens width + bridge width = approximate frame PD. A 52-18 frame has approximately 70mm frame PD (52 + 18 = 70). If your PD is 70mm, good match. If your PD is 58mm, that frame will require significant decentration.

For the best results, choose frames where your PD falls within a few millimeters of the frame's natural PD.

Lens Selection Considerations

Your PD interacts with lens options:

High-Index Lenses

If you have a strong prescription and choose high-index material for thinner lenses, PD accuracy becomes more important. The benefits of high-index diminish when you're looking through off-center portions of the lens.

Progressive Lenses

Online progressive ordering is higher risk than single vision. The fitting is more complex (PD plus segment height plus other parameters), and the consequences of errors are more severe.

If you order progressives online:

Use monocular PD (non-negotiable)
Select frames with appropriate height for progressive corridors
Be prepared for possible adaptation challenges or return

Many first-time progressive wearers benefit from in-person fitting for their first pair, then potentially ordering online replacements once they know what works.

Prism Prescriptions

If your prescription includes prism, be especially careful with PD. The interaction between prism positioning and optical center positioning is complex. Consider professional fitting for prism prescriptions.

Before You Order: Final Checklist

Run through this checklist before completing your order:

Prescription:

[ ] Current and unexpired
[ ] All values correctly entered
[ ] ADD power included if needed

PD:

[ ] Measured (not guessed or estimated)
[ ] Entered in correct format (single vs. dual)
[ ] Verified before submission
[ ] Compatible with selected frame

Frames:

[ ] Size appropriate for your face
[ ] PD compatible (check frame measurements)
[ ] Adequate height for lens type (especially progressives)

Lenses:

[ ] Appropriate material for your prescription
[ ] Coatings selected as desired
[ ] Lens type matches your needs

What to Do When Glasses Arrive

When your online glasses arrive:

Immediate Inspection

Check for obvious defects:

Lens scratches or flaws
Frame damage
Correct frame color and style

Prescription Verification

If possible, have the prescription verified. Many local optical shops will check prescription accuracy for a small fee or free. This confirms what you ordered is what you received.

PD Verification

Similarly, have the optical center distance measured. Compare to what you specified. Discrepancies indicate manufacturing error.

Wear Test

Wear the glasses under normal conditions for 1-2 weeks (unless problems are obvious). Note any symptoms: headaches, eye strain, blur, discomfort.

Return Policy Awareness

Online retailers typically offer 30-day return policies. Track your return window. Don't wait until day 29 to decide there's a problem.

Troubleshooting Online Glasses

If something seems wrong:

Vision Isn't Clear

Could be:

Prescription error (what was made doesn't match what was prescribed)
PD error (you're looking through the wrong part of the lens)
Adaptation needed (legitimate adjustment period for new prescriptions)

Get the glasses' prescription and PD verified professionally. This isolates the problem.

Headaches or Eye Strain

Often indicates:

PD error (you provided wrong number or they made lenses wrong)
Prescription error
Frame fit issues (vertex distance, tilt)

If PD measurement of the glasses doesn't match your actual PD, there's your answer.

Just Feels "Off"

Sometimes glasses are technically correct but feel wrong. This can reflect:

Different lens design than you're used to
Different frame fit
Minor but noticeable optical differences

Give it the full adaptation period, but don't force yourself to adapt to something fundamentally wrong.

Return and Remake Policies

Reputable online retailers offer:

Return period: 30+ days to return unworn/undamaged glasses
Remake policy: Free redo if they made an error
Exchange options: Swap for different frames or lenses

Keep all packaging until you're certain you'll keep the glasses. Document any problems with photos. Contact customer service early if issues arise.

The Savings Calculation

Online glasses make financial sense when you:

Provide accurate measurements
Choose appropriate frames
Select sensible lens options
Understand you're trading convenience for savings

If you have complex needs (high prescription, progressives, prism, first-time wearer), the risk of problems increases. You might get one pair professionally fitted and order subsequent pairs online.

For straightforward prescriptions with accurate PD, online ordering is often a no-brainer. Why pay $400 for what you can get for $100?

The Bottom Line

Online glasses purchasing transfers responsibility from sales staff to you. That responsibility isn't complicated, but it does require attention to detail.

PD is the most commonly botched detail because most people don't know their PD and don't understand its importance. Now you do.

Get your PD right. Verify your entry. Choose compatible frames. And enjoy glasses that cost a fraction of retail while working exactly as they should.

Ready to order online? Get your PD first. Our free measurement tool takes 30 seconds and gives you both binocular and monocular readings.