Ditto, 6over6, Premium Vision and ExpressExam have joined forces and are now Luna.

Accurate Online PD Measurements

Ditto is launching a new product that will measure a customer's pupillary distance within +/- 1mm of accuracy in the large majority of cases. TruePD™ is Ditto’s PD technology for card-based and depth-camera based measurements.

The Importance of Pupillary Distance

Pupillary distance (“PD”) measures the distance between the centers of the left and right pupils. This measurement is used by lens labs when adding prescription lenses to eyewear frames to properly determine where to put the focal center of the prescription lenses.  It’s very important to get this measurement correct so that customers can see well in their prescription eyewear and eCommerce retailers can unblock online sales and avoid costly returns and remakes.

The average PD for an adult is between 54-74 mm and the average PD for a child is between 43-58 mm. PD is usually measured during an eye exam using an autorefractor or pupilometer. These devices aren’t perfect however and typically have +/-1mm of error.  

Many eye care professionals don’t provide the PD measurement on their patient’s prescription because they don’t want them to be able to purchase eyewear elsewhere. This creates a blocker for customers and sets up a poor eyewear shopping journey. In fact, customers typically don’t know what PD is or that they need it to purchase prescription eyewear so they don’t know to ask for it with their prescription.  To try and address this problem, most eCommerce sites provide ruler-based methods to calculate PD which are inaccurate and confusing for customers. Alternatively, customers can contact their optometrist to obtain their PD but it can be hard to track down.

Online eyewear retailers need a precise, user-friendly way for their customers to measure their PD.  

Introducing TruePD™

Ditto is launching a new product that will measure a customer’s pupillary distance within +/- 1mm of accuracy in the large majority of cases. TruePD™ is Ditto’s PD technology for card-based and depth-camera based measurements.  TruePD™ is surfaced in our existing Face Insights offering and a new TruePD™ UI detailed below.

We have been in research and development on this product for over two years and are incredibly proud we have achieved a level of accuracy comparable with the equipment used in optical stores and doctor’s offices. This achievement will meaningfully help customers have better access to their PD.


TruePD™ provides eCommerce retailers with a fast, simple, and accurate way to obtain customer PD’s.  TruePD™:

  • Removes a key blocker to online sales which will increase conversion rate
  • Reduces returns from inaccurate PDs
  • Improves the customer experience by removing the burden for a customer to manually measure their PD with a ruler or track it down from their optometrist

When coupled with other Ditto products, TruePD™:

  • Improves the accuracy and fit of virtual try-on 
  • Enables more relevant frame recommendations

How It Works

Ditto’s TruePD™ will work in two ways:

  1. On the web using a standard-sized card from your wallet
  2. On an Apple mobile device with a TrueDepth sensor (iPhoneX+, iPad Pro, etc.)

Web-Based PD

Customers can obtain their PD in a few simple steps.

  • Customers will need a standard-size plastic card. We use this as a reference object to understand scale and calculate PD accurately
  • Customers will need to ensure their face is well lit to improve pupil detection
  • Once the customer is ready, they will need to provide camera access in their browser when prompted and then they’re ready!

  • Customers will need to perform a 5-second scan of their face from left-to-right. We capture the face from 180° to reconstruct it in 3D to reduce error and improve accuracy

Note: If a scan has already been captured from a previous try-on scan, then this step can be skipped. See Use Cases below

  • Once the scan is complete the customer will now need to grab that plastic card to do “card-scale”.
  • The card needs to be held flat against the forehead
  • (A short video snippet is provided to demonstrate how to do this correctly)
  • We then take the scan and the card-scale image to calculate your customer’s PD
  • To finish it off, we display the measurement on the screen to the customer, but also return it as data so retailers can save it to their account and include it with their order details

Apple Mobile Device PD

On an Apple mobile device with a TrueDepth sensor, the experience is both easier and faster! Customers using Apple’s Safari browser will be able to skip the “card-capture” step referred to above and just do the scan.  TrueDepth technology enables us to understand real-world scale without needing a card as a reference object. Note: this will be included in a future release planned for late 2021.

What Do We Measure?

When TruePD™ launches we will be measuring far PD.  In future versions near PD and DualPD measurements will be included.

Use Cases

Seamless Integration with Ditto’s Virtual Try-On

TruePD™ uses the same facial scan as Ditto’s Try-On; this provides flexibility in how PD can be surfaced to your customer and save them time.  Here’s how:

  • If an eCommerce retailer is using Ditto’s Face Insights product they can choose to surface the TruePD™ measurement (along with other facial insights) to their customers following a try-on scan
  • If an eCommerce retailer decides to capture and display PD with TruePD™ elsewhere in the customer journey (see below), their customer can skip the scan step and just  perform “card-scale” to obtain their PD

Getting PD Post Purchase

If an eCommerce retailer plans on obtaining their customer’s PD as part of a checkout process, our recommended best practice is to integrate TruePD™ after the purchase is made. This ensures no friction is added to the purchase funnel.

It makes sense to obtain PD along with other prescription information required to fulfill an order. The TruePD™ UI can be integrated in-line or as a popup (iFrame) on any page.  Once measured the UI will display the PD value, but the value is also returned as data that a retailer can save to their customer’s account or otherwise associate with the order.

Acquiring New Customers

Many eCommerce websites have content created to educate customers about PD and provide guidelines on how to calculate it with a ruler.  In many cases these pages are SEO designed to attract general search traffic and acquire new customers.

These pages are a great place to add TruePD™ and then drive visitors towards account creation.

The TruePD™ UI can be integrated in-line or as a popup (iFrame) on your PD.  Once measured the UI will display PD value, but the value is also returned as data that can be stored on a customer’s account or otherwise saved to associate with an order.

Some competitors charge several dollars per PD which doesn’t lend itself to using it for this use case.  Ditto’s pricing model will remove this concern so our clients can focus on delivering the best experience to their customers.


The need for an accurate PD is a blocker to online sales.  Unfortunately eCommerce retailers have needed to ask their customers to jump through hoops to obtain it. With the launch of Ditto’s TruePD™ offering, eCommerce retailers have a fast, simple, and accurate way to obtain their customers’ PD that works seamlessly with Ditto’s Virtual Try-On technology. 


Forward-looking eyewear retailers choose Luna

Ditto is now Luna.

Ditto along with 6over6, Premium Vision, and ExpressExam have joined forces to bring an integrated offering to the vision industry — rebranding as Luna. 

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