An unlabeled pair of progressives shows up at the bench, the ink layout has been cleaned off, and there’s no work order to check against. Every progressive lens still carries the information needed to identify it: two permanent laser engravings, spaced 34 mm apart and centered on the lens’s prism reference point (PRP), that survive cleaning, reglazing, and years of wear. The engraving beneath the temporal (ear-side) mark states the add power in diopters; the one beneath the nasal (nose-side) mark identifies the manufacturer, design, and material index. Once you’ve located those two marks, the manufacturer’s layout chart tells you exactly where the fitting cross, the 180° line, and the PRP belong, so you can re-ink the lens and verify it without the original order in hand.
Two Sets of Marks, Two Different Jobs
Every progressive lens carries two independent marking systems, and mixing them up is the most common reason a lens looks like it has “lost” its layout. Temporary ink markings, applied at the dispensing bench, are non-permanent marks removed before the wearer takes the glasses home. The Vision Council’s Lens Marking Guidelines define them as markings “utilized to position the lens during layout blocking and to verify the power and position of the lens during inspection and dispensing.” They include the fitting cross, the 180° axis line, and circles marking the distance and near reference points, and every one of them wipes off with isopropyl alcohol.
Permanent markings are a different animal: semi-visible engravings cut into the lens’s front surface, either as a mould imprint on semi-finished blanks or, on most lenses made today, by an excimer laser that removes a tiny amount of material from the surface, the same laser-ablation approach used elsewhere in how lenses are made. The Vision Council describes them as “irremovable markings on the lens… often utilized to identify the brand and addition power of the lens… and to provide reference points for reapplying temporary markings.” Because they survive cleaning and years on someone’s face, they’re what you fall back on once the ink is gone.
The Alignment Reference Marks: 34 mm Apart, Centered on the PRP
The two alignment reference marks, sometimes called ARM or micro-markings in manufacturer literature, anchor everything else on the lens. The Vision Council’s guidelines, written in accordance with ANSI Z80.1 and ISO 8980-2, specify that progressive lenses carry “two alignment reference markings comprising two marks with their centers separated by a distance of 34 mm ±0.5 mm, equidistant to a vertical plane through the PRP and located vertically at the height of the PRP.” That spacing appears on every pair of progressive lenses, regardless of manufacturer or design, which is what makes the marks useful as a universal reference rather than a brand-specific one. ISO 8980-2:2004, the international standard for uncut finished progressive power lenses, is the normative source both guidelines point back to.
The prism reference point itself isn’t a visible mark. The Vision Council defines the PRP as the point “located at the midpoint between the semi-visible alignment reference markings (or ‘engravings’)… separated by a distance of 34 mm, along a horizontal axis bisecting those two markings,” or, in plain terms, 17 mm to each side of it. The PRP also sits at the center of a 30 mm exclusion zone: “No permanent markings that could impair the visual function of the lens should appear within this 30-mm Exclusion Zone.”
Reading the Add Power and Manufacturer Engravings
The two alignment marks also anchor the lens’s other permanent data. The Vision Council’s guidelines state plainly that the add power “should appear directly below the temporal alignment reference marking,” while an indication of the manufacturer, supplier, tradename, or trademark “should appear… directly below the nasal alignment reference marking.” ABDO’s reference on hidden markings on progressive power lenses describes the same convention from the practitioner’s side: “A typical set of product identification marks show a temporal engraving, which identifies the addition and a nasal engraving, which identifies the product design and the refractive index.”
In practice: ear side, add power; nose side, brand, design name, and material index. American Optical’s AO PRO 15, for example, engraves an add-power symbol under the temporal mark and the code “PRO” under the nasal mark to identify the design and refractive index. The exact code differs by manufacturer, and often by material within the same design line, so an engraving you don’t recognize is worth checking against that brand’s identification chart rather than guessing. As ABDO notes, “commercially available progressive lens identifiers can also be purchased” for shops that see a wide mix of brands.
One detail worth knowing: if a lab compensates the fabricated prescription (a power adjustment applied during manufacturing), the guidelines call for “a carat (^) symbol… placed below the temporal alignment reference marking,” to the temporal side of the add-power marking, flagging that the finished lens intentionally differs from the original order.
Progressive Lens Marking Reference Table
| Marking | What It Is | Where It Sits | How It’s Used |
|---|---|---|---|
| Alignment reference marks | Two permanent laser engravings | 34 mm apart, 17 mm either side of the PRP, at PRP height | Re-establish the PRP and horizontal layout once ink markings are gone |
| Add power engraving | Permanent, manufacturer-coded engraving | Directly below the temporal alignment mark | States the near addition without needing a lensmeter reading |
| Manufacturer/design engraving | Permanent logo, design, and material-index code | Directly below the nasal alignment mark | Identifies brand, lens design, and refractive index |
| Prism reference point (PRP) | Reference point, not a visible symbol | Midpoint between the two alignment marks | Where prism and thickness-reduction prism are measured |
| Fitting cross | Temporary ink mark | A manufacturer-set distance above the alignment-mark line | Positions the lens over the wearer’s pupil during dispensing |
| 180° line | Temporary ink line | Horizontal, through or near the PRP | Confirms axis and rotation alignment in the frame |
| Exclusion zone | Defined area, not a mark | 30 mm circle centered on the PRP | No permanent marking that could impair vision may appear inside it |
How to Find and Restore Hidden Engravings on the Bench
A hard coat or anti-reflective coating that protects the lens also lowers the contrast of the marks underneath it, which is why ABDO’s guidance warns that finding them “can sometimes be very difficult, particularly if the lens has subsequently been hard and multi antireflection coated.” A few techniques help:
- Angle the lens under a strong point light source against a matte black background and inspect with a loupe or magnifier. As ABDO puts it, “the use of a strong light source against a matt black background and a good magnifying glass will often pick them out.”
- Hold the lens up to diffuse light, a window or a ceiling fixture, and rock it slightly. The engraved area catches the light differently from the surrounding polished surface.
- Breathe lightly on the lens. The fog clears unevenly over the engraved area, making the marks visible for a second or two before the surface dries. This works best on glass and on a cool lens.
- For a shop that sees a wide mix of brands, a backlit progressive lens identifier speeds this up and can cross-reference the code against a manufacturer database.
Once you’ve located the two alignment marks, dot them directly with a fine-point marking pen, then pull that manufacturer’s layout chart to plot the fitting cross, the 180° line, and the PRP relative to those two dots. ABDO calls this sequence, finding the engravings, marking them, and rebuilding the ink layout from the chart, “restoration” of the markings. After the layout is restored, verify the actual add power and prism against the engraved values with a digital lensmeter before the glasses go back to the wearer.
Using the Engravings to Verify Fit and Troubleshoot a Complaint
When a patient returns with a non-adapt complaint, the permanent engravings are the fastest way to rule out a manufacturing or ordering error before re-checking segment height or vertex distance. If the PRP the engravings define doesn’t line up with where the ink fitting cross was placed at dispensing, or the engraved add power doesn’t match the order, that’s grounds to send the lens back rather than repeat a refraction. Several of the errors covered in this progressive lens fitting errors checklist trace back to exactly this kind of mismatch between where the engravings say the lens is built to sit and where it was actually mounted.
What the engravings can’t tell you is whether the frame was fit to the correct pupillary distance or segment height in the first place. They only confirm what the lens itself was built to be. An accurate PD and seg height measurement at the point of dispense is still what keeps a fitting cross from drifting far enough off the alignment marks to need restoring at all.
Frequently Asked Questions
How do I find the hidden markings on progressive lenses?
Angle the lens under a strong light source against a matte black background and inspect it with a loupe or magnifier; ABDO notes this combination will “often pick them out” even on coated lenses. Breathing lightly on the lens also works: the fog clears unevenly over the engraved area for a second or two. For shops that see many brands, a backlit progressive lens identifier speeds up the process and cross-references the code.
How can you tell if a lens is progressive rather than single vision?
Hold the lens a few inches in front of a straight line, a door frame works, and tilt it side to side. A progressive lens produces a wavy, swimming distortion near the lower half because of the corridor’s continuously changing power; a single-vision lens does not. To confirm, find the two permanent alignment marks about 34 mm apart near the horizontal center and check the engraving under the temporal mark: an add-power value there confirms a progressive design.
Where is the add power engraved on a progressive lens?
Directly below the temporal, ear-side, alignment mark, expressed in diopters. The Vision Council’s marking guidelines and ABDO’s practitioner reference both describe the same placement. The exact numeric code is set by the manufacturer, so check an unfamiliar one against that brand’s identification chart rather than assuming a single universal format.
What is the fitting cross, and how is it different from the permanent engravings?
The fitting cross is a temporary ink mark, defined by The Vision Council as “that point on a lens… used as a reference point for positioning the lens in front of a patient’s eye.” Unlike the alignment engravings, it wipes off during cleaning and has to be reapplied from the manufacturer’s layout chart if it’s lost.
Are progressive lens engravings standardized across manufacturers?
The spacing and placement are standardized. ISO 8980-2 and ANSI Z80.1 both specify alignment marks 34 mm apart, an add-power engraving under the temporal mark, and a brand/design engraving under the nasal mark. The specific codes used for add power, material, and design vary by manufacturer and lens range.
Why can the alignment engravings sometimes be seen when wearing the glasses?
Per ABDO’s technical reference, this is normally a symptom of an uncoated lens. A hard coat or anti-reflective coating reduces the visibility of the marks, so switching to a coated lens or adding a coating typically resolves the complaint.
I grew up inside an optical shop. My mother likes to tell how, as a kid, I would watch eyeglasses being assembled, play with the tools, and draw on the back of service order slips. The family business taught me early what a precise measurement and work done right are worth.
I went on to spend more than twenty years as a software engineer, always keeping an eye on the optical world. Optogrid was born where the two meet: digital measurement technology (pupillary distance and fitting heights) built by someone who knows the dispensing counter from the inside.