Surgeon at the operating table while a colleague holds a tape measure from her nasal radix down to her instrument tips

Measurements

Measure once.Build around you.

Accurate pupillary distance and working distance help your loupes align with your eyes, your posture, and the way you actually work.

Measure PD with an app Shop loupes Measure working distance

The process

6 steps. Two numbers that matter.

Measure pupillary distance

Pupillary distance is the gap between the centres of your pupils, in millimetres. It determines where the two optical barrels converge, so it carries the least tolerance of any measurement here — aim to be within 1 mm. Use a well-reviewed smartphone PD app, or hold a ruler across your brow in good lighting and read the distance between pupil centres while looking straight ahead at a fixed point several metres away. Take the measurement three times and use the average; a single reading is where most errors come from. If you have an eyeglass prescription from the last couple of years, the PD is often printed on it already, and an optician-measured PD is more reliable than either method above.

The quickest accurate way to measure PD at home is a dedicated measurement app. We recommend these two:

Free · iPhone and iPad (iOS 17 or later)

The Framery (formerly GlassesOn)

By 1-800 Contacts, originally developed by 6over6 Vision

Hold any card the size of a credit card flat against your forehead for scale. The app uses your front camera and voice prompts to measure your PD in under a minute.

Registered with the FDA as a Class I exempt medical device.
Clinically tested to the ANSI Z80.17 standard: PD within 2 mm.

Get it on the App Store

Free · iPhone X or newer, and iPads with Face ID

EyeMeasure

By Bonlook

Uses the Face ID (TrueDepth) depth camera, so you need no card, mirror or ruler. Hold the phone about 30 cm from your face. It reports near and far PD.

The developer states accuracy to within 0.5 mm.
Works only on devices with a Face ID camera.

Get it on the App Store

Take three readings and use the average. Loupes need PD within about 1 mm, which is tighter than the 2 mm tolerance used for everyday glasses, so repeat readings matter.

On Android? Neither app is currently on Google Play. Use an optician-measured PD, the PD printed on a recent glasses prescription, or the ruler method described on our measurements page.

Pupillary distance

Clinician in a surgical cap holding a millimetre ruler across her brow, with pupil centres marked 63 mm apart

Measure working distance

Working distance is the straight line from your nasal radix, the deepest point of the bridge of your nose between the eyes, to the exact point where your instrument tips meet tissue, measured in your natural clinical posture. Set yourself up as if you were mid-procedure — same table or chair height, same patient position, same distance from the field — and have a colleague run the tape while you hold still. Most clinicians land somewhere between 350 mm and 500 mm, but the number that matters is yours rather than the average. This measurement is what every other decision hangs off: it sets the focal length the optics are cut to, and on fixed-distance models it cannot be changed afterwards.

Working distance · Standing

Nasal radixWorking point565 mm

Working distance

0mm

Example reading from this drawing, which is to scale. Yours will differ.

Check your posture before you trust the number

This is the step people skip, and it is the one that decides whether the loupes help your neck or quietly hurt it. Measure with your back straight, shoulders down, and neck close to neutral — not hunched toward the field. If you measure while leaning in, you build that lean permanently into the optics and then spend years working in the posture you were trying to escape. Ergonomic prismatic models such as Apollo and Medusa refract the view downward so your head stays up and your eyes look straight ahead, but they can only do that if the working distance was measured from an upright posture in the first place.

Posture reference

Decide whether your working distance is fixed or variable

If you work in one consistent posture, a fixed working distance is correct and simpler. If you genuinely move between seated and standing work through the day, or between procedures with very different ergonomics, a single fixed number will be a compromise at both ends. Medusa adjusts in real time from 300 mm to 600 mm for exactly that reason. Deciding between fixed and adjustable before you measure is worth doing, because it changes how much the precision of any single reading matters.

Add your prescription, if you need one

Prescription lenses are a $200 add-on across the lineup. Provide a current eyeglass prescription, ideally issued within the last two years, alongside your other measurements. The prescription is carried in a lens behind the optics rather than in the barrels, which means it can be updated later without rebuilding the loupes. If you wear contact lenses during clinical work and glasses the rest of the time, measure and order for the way you actually work.

Submit after checkout

Once you have ordered, you will receive a measurement link by email. Enter your pupillary distance, working distance, and prescription details there, and production starts from those numbers. There is no dealer, no rep visit and no fitting appointment anywhere in this process — the measurements are the fitting, which is why they are worth taking carefully. If anything needs adjusting when the loupes arrive, the frame can be fine-tuned with our guidance.

Evidence note

Smartphone PD apps are accurate enough for your loupe order.

A 2023 peer-reviewed study compared smartphone pupillary distance applications against a digital pupilometer and confirmed that the leading apps measure accurately enough to support a confident loupe order from home. Pick a well-reviewed app, take the measurement in steady, even light with the phone held level, and repeat once for consistency — that gives us the precise PD your HeliosX loupes are built around.

Read the PubMed Central study

Questions

Measurement FAQ

What measurements do I need for HeliosX loupes?

Three things: pupillary distance, working distance, and a current eyeglass prescription if you want prescription lenses fitted. Pupillary distance and working distance are the two that determine how the loupes are built, and both can be measured accurately at home in a few minutes. Everything else — frame choice, magnification, declination — is a selection rather than a measurement.

How accurate does my pupillary distance need to be?

Within about 1 mm. PD sets where the two optical barrels converge, so an error here shows up as eye strain rather than blur — your eyes compensate for a few minutes and then start to fatigue. This is why it is worth taking the measurement three times and averaging it rather than trusting a single reading.

Can I use a smartphone app for pupillary distance?

Yes, and most customers do. Accuracy varies between apps, so repeat the measurement two or three times and use the average. If you have an eyeglass prescription from the last couple of years, the PD is often printed on it, and an optician-measured PD is the most reliable source of all. Any of these three routes is fine.

What happens if my working distance is wrong?

You adapt your posture to the loupes instead of the other way round — which is the exact problem loupes are meant to solve. Too short and you lean in; too long and you sit back and lose the benefit of the magnification. Neither damages the loupes, but both undo the ergonomic case for wearing them, and the effect compounds over years of clinical work.

Which HeliosX model has adjustable working distance?

Medusa. It adjusts in real time from 300 mm to 600 mm, which is why it suits clinicians who move between seated and standing work within the same day. Every other model is built to one fixed working distance taken from your measurement, so on those the number matters more.

Should I measure sitting or standing?

Measure in the posture you actually work in most of the time. If that is genuinely split between seated and standing, either measure the position you spend more hours in, or choose Medusa and adjust between them. Do not average two very different postures into a number that matches neither.

How do you fit loupes without an in-person appointment?

The measurements that matter — pupillary distance and working distance — are numbers, and numbers travel. A fitting appointment largely exists because a dealer needs you in the room; it is a sales structure rather than an optical requirement. We have no dealer network, so we take the measurements online, build to them, and help you adjust the frame on arrival if anything needs refining.

When do I submit my measurements?

After checkout. You will receive a measurement link by email, and production starts once those numbers are in. Taking payment first is simply how the build queue is ordered — nothing is cut or assembled until we have your measurements.

Can I get prescription lenses fitted?

Yes, as a $200 add-on across the lineup. Provide a current eyeglass prescription — ideally issued within the last two years — along with your other measurements. The prescription sits in a carrier lens rather than in the barrels themselves, so it can be updated later without rebuilding the loupes.

What if the fit is not right when they arrive?

Contact us. Frame adjustments — temple arms, nose bridge, angle — are routine and can usually be resolved with guidance. If a measurement was genuinely wrong rather than slightly off, that is a different conversation, and we would rather have it than leave you with loupes you avoid wearing.