'Lens marks' on brand new spectacles - WTF?

[Mangetout]

I just stopped postponing the inevitable and spent a painful amount of money on some new spectacles. I have quite a high prescription (about +6 dioptres), so I have to go for the extra-spendy high index optical plastic, or the lenses come out like coke bottles.

Anyway… I picked up the new specs on Wednesday and started wearing them - after the initial normal weirdness of adjustment, I started noticing a little blurry spot in the right lens - between the centre point and a two o’clock position on the rim.

I dismissed it as a bit of dirt or grease, but on returning home and cleaning with the microfibre cloth, it was still there. Holding the glasses up to the light, so that I could focus on the lenses themselves (the subject field appearing blurred through them), I noticed a little swirly sort of artifact in the lens at that point. There was a very similar one on the left lens too, but it was right near the rim at the top, and my left eye is lazy anyway, so I hadn’t noticed it.

I took them back to the opticians today, saying that I’d found a blemish or defect in both of the lenses - the person in the store examined them for a while, then told me “they’re lens marks”.

At first, I thought this just meant they were flaws or blemishes in the lens surface or material, but she went on to explain that they are marks deliberately etched or engraved on the lenses, for some technical reason to identify the lens material, prescription, or orientation or something like that.

So they are supposed to be there - I think she expected I would just shrug and accept them at this point, but I explained that they were causing a blurred spot in my vision that I couldn’t ignore.

She went off to talk to the people in the instore lab and came back promising that they’d try to make another pair of lenses without the marks this time - but as if this was something difficult to do.

So my questions (after all that waffle) are:
What are these lens marks for - are they really essential on the finished product?
Is it normal for them to be placed like that in the middle of the lens?
Are they unnoticeable in lenses of lower prescription?

[cromulent]

Were they progressive lenses? These do come with markings, which are used to ensure that the lenses fit you correctly and also used verify the add power.
I haven’t heard of non-progressives carrying markings, although it’s possible some lens companies do. Most people aren’t bothered by progressive markings (and in fact won’t notice it until you point it out.)

[cromulent]

Also, to answer your questions – they’re usually towards the periphery of the lens, not the middle. But there are a few marks, actually, in a progressive lens, and depending on how the lens is set in the frame, potentially be close enough to your center of vision to be annoying. The thing about progressives, however, is people tend to look through certain defined parts of the lens since the other areas are “non-optical” and won’t provide good vision anyway, so the lens marks will be in these “non-optical” areas. I never heard of them being more noticeable depending on the prescription.

[Mangetout]

I’m not sure what you mean by progressive lenses - is that what might be described here as ‘varifocal’? If so… no - they’re single-vision, aspheric lenses.

[Mangetout]

I should try to describe the marks… they were not so much discernible as marks, as they were patterns of disturbance in the otherwise smooth function of the lens. Imagine a window coated with a flawless and smooth, thin layer of water - so smooth as to be neutral to vision.
Now someone dabs away a tiny patch of the water with their finger - leaving an unevenly-dryish spot - that’s what it looked like. Not opacities - just little swirly refractive disturbances.

[cromulent]

Well, I have no idea then. I never heard of that (which doesn’t mean, of course, that it doesn’t exist.) Sorry!

[CalMeacham]

I’m not sure what you mean by progressive lenses - is that what might be described here as ‘varifocal’? If so… no - they’re single-vision, aspheric lenses.

Progressive lenses are like bifocals, only the transition between one focal region and the other isn’t abrupt, as in a classical bifocal, but changes gradually – progressively, hence, the name.

You’d think that this would lead to one region on the bottom and another o the top, but there is a weird characteristic shape to progressives, with large unusable areas on the side, that I’ve never understood (and I have an advanced degree in optics).

The prescription in the transition region isn’t well-defined, but it shouldn’t look the way you describe. You ought to get an image (perhaps somewhat distorted), but you shouldn’t get a blur.

Progressive lens

If you scroll down this page you get a picture of the Zones, with the two useless areas to either side:

The Advantages of Progressive Lenses Over Bifocals and Trifocals

[Mangetout]

@CalMeacham

Progressive lenses are like bifocals, only the transition between one focal region and the other isn’t abrupt, as in a classical bifocal, but changes gradually – progressively, hence, the name.

That indeed sounds like what is called varifocal here in the UK.

And my glasses aren’t that kind - they’re single vision lenses.

[Mr.Miskatonic]

The sad fact is that commercial eyeglasses get a ridiculously low amount of polishing for the service they must render. Lenses in a cheap pair of binoculars gets much better treatment.

Part of this is the need for many different sizes, shapes, and powers of eyeglass lenses. But another part is the desire for high margins by keeping costs (like polishing) low.

[RealityChuck]

I’m pretty sure they commonly used on lenses. The basic idea is to indicate the prescription. Thus, if you go to a new eye doctor, they can look at your glasses and know your current prescription without having to find it.

Optometrists and opticians use sort of a microscope to see the marks. Years ago, I thought that it somehow sent light through the lens and figured out the prescription, though the idea of a mark is obviously simpler and more effective.

Now, they’re supposed to be on the periphery of the lens and outside your normal line of sight. On one pair of glasses I owned, the marks were quite noticeable if you looked at the lenses, but once you put them on, they didn’t affect your vision.

They can probably custom make lenses without the marks, but that could cause problems if your optometrist doesn’t know your prescription. They could just test, but they wouldn’t know if the new prescription is a small change or a major one that might indicate a more serious problem.

[Napier]

@Mr.Miskatonic

The sad fact is that commercial eyeglasses get a ridiculously low amount of polishing for the service they must render. Lenses in a cheap pair of binoculars gets much better treatment.

Part of this is the need for many different sizes, shapes, and powers of eyeglass lenses. But another part is the desire for high margins by keeping costs (like polishing) low.

Polishing? Do you mean the optometrist’s shop saying they are “grinding your lenses”? I think they are being a little misleading by saying what sounds like the glass grinding process used for many lenses, but in the case of eyeglasses they use polished molds to mold lenses and grind the edges to fit the frames you want. Simple single-vision lenses without options like coatings are common enough to stock, but when you consider all the degrees of freedom for bifocal or trifocal or progressive lenses with various options, they can’t really stock all of them.

Hope I have this right - it’s based in part on industry advertisements I have seen for the molding machines.

[aruvqan]

@Mr.Miskatonic

The sad fact is that commercial eyeglasses get a ridiculously low amount of polishing for the service they must render. Lenses in a cheap pair of binoculars gets much better treatment.

Part of this is the need for many different sizes, shapes, and powers of eyeglass lenses. But another part is the desire for high margins by keeping costs (like polishing) low.

tell me about it, the best glasses I ever had were made by leica. sniff i really miss them. Uncoated glass, but the same glass they make lenses out of, and they ground them at their facility and sent them to my optometrist.

[Mr.Miskatonic]

@Napier

Polishing? Do you mean the optometrist’s shop saying they are “grinding your lenses”? I think they are being a little misleading by saying what sounds like the glass grinding process used for many lenses, but in the case of eyeglasses they use polished molds to mold lenses and grind the edges to fit the frames you want. Simple single-vision lenses without options like coatings are common enough to stock, but when you consider all the degrees of freedom for bifocal or trifocal or progressive lenses with various options, they can’t really stock all of them.

Hope I have this right - it’s based in part on industry advertisements I have seen for the molding machines.

Even with casting you need to have at least a minimum of post-mold polishing. Otherwise your lenses will be translucent, not clear. Cast lenses start off as pretty poor lenses, but they can be made to yeoman work levels if given some care during manufacture. Eyeglass lenses don’t get that kind of attention.

[cromulent]

@RealityChuck

I’m pretty sure they commonly used on lenses. The basic idea is to indicate the prescription. Thus, if you go to a new eye doctor, they can look at your glasses and know your current prescription without having to find it.

Optometrists and opticians use sort of a microscope to see the marks. Years ago, I thought that it somehow sent light through the lens and figured out the prescription, though the idea of a mark is obviously simpler and more effective.

Now, they’re supposed to be on the periphery of the lens and outside your normal line of sight. On one pair of glasses I owned, the marks were quite noticeable if you looked at the lenses, but once you put them on, they didn’t affect your vision.

They can probably custom make lenses without the marks, but that could cause problems if your optometrist doesn’t know your prescription. They could just test, but they wouldn’t know if the new prescription is a small change or a major one that might indicate a more serious problem.

Except I’m a second-year optometry student and have never heard about marking the prescription on any single-vision lenses or bifocals, or anything that wasn’t a progressive lens (or varifocal, as the OP calls it.) We do use a lensometer, which sends light through the lens, to determine the prescription. I just had an assessment on that one month ago!

It’s entirely possible that there are some manufacturers that mark the prescription on single vision lenses, but it is not common practice.

[Mangetout]

@Napier

Polishing? Do you mean the optometrist’s shop saying they are “grinding your lenses”? I think they are being a little misleading by saying what sounds like the glass grinding process used for many lenses, but in the case of eyeglasses they use polished molds to mold lenses and grind the edges to fit the frames you want. Simple single-vision lenses without options like coatings are common enough to stock, but when you consider all the degrees of freedom for bifocal or trifocal or progressive lenses with various options, they can’t really stock all of them.

Hope I have this right - it’s based in part on industry advertisements I have seen for the molding machines.

I’m not sure that can have been what has happened here - they had to send off for lens blanks because I chose a high index plastic (to minimise thickness) - and they chose the blanks from a selection of different diameters so that after grinding and trimming to fit the frame, edge thickness would be minimised.

[AquaPura]

@cromulent

Except I’m a second-year optometry student and have never heard about marking the prescription on any single-vision lenses or bifocals, or anything that wasn’t a progressive lens (or varifocal, as the OP calls it.) We do use a lensometer, which sends light through the lens, to determine the prescription. I just had an assessment on that one month ago!

It’s entirely possible that there are some manufacturers that mark the prescription on single vision lenses, but it is not common practice.

Cromulent is correct. There are no markings on single vision lenses that show the power of the lens. The lens power is easily read through a lensometer (the microscopey looking dohickey). As far as I am aware none of the common lens manufactures use any sort of “watermark” in the lens to indicate power or orientation unless that lens is a varifocal (progressive).

If the marks you see are sort of swirly areas of distortion, they are likely artifacts from the polishing, or moulding process of the lens. They are not intentional, and they should not be there. Its possible whomever surfaced the lenses (ground them to your Rx) b0rked up the polishing, or the someone whomped their big butt against the lens molder, causing a flaw. However, this would be unlikely as a random chance in both lenses.

Lenses can be easily damaged in the blocking and unblocking process for edging (cutting out the lens to fit your frames) that is likely what happened.

Take 'em back until they cough up lenses without swirlies.

P.S. Get the antireflective coating. It’s the bee’s knees.

~Aqua
Optician ABO, NCLE

[AquaPura]

@Napier

Polishing? Do you mean the optometrist’s shop saying they are “grinding your lenses”? I think they are being a little misleading by saying what sounds like the glass grinding process used for many lenses, but in the case of eyeglasses they use polished molds to mold lenses and grind the edges to fit the frames you want. Simple single-vision lenses without options like coatings are common enough to stock, but when you consider all the degrees of freedom for bifocal or trifocal or progressive lenses with various options, they can’t really stock all of them.

Hope I have this right - it’s based in part on industry advertisements I have seen for the molding machines.

Ooooo… if only most places could afford those nifty custom molding machines. They are indeed keen. However, they are h00ge (size of a semi) and really really REALLY pricey.

They really MAY be grinding his lenses. Though it isn’t as common as shops that just have an edger to cut out the lenses to fit the frame, some shops do have the equipment to surface grind lenses, and that sounds like what they have done with his lenses. The lens blanks come in a variety of “base curves” the base curve chosen is based on what Rx is needed for the lens. These lens blanks also come in a variety of materials, and styles so the lab can cut many many more Rxs that a basic edging lab who just has a certain selection of powers. With a surfacing lab, one can do anything, it just depends on how much equipment you want to stuff in a little shop. Most eyeglass store labs send out any lenses that need custom coatings, as those are the pricey and stinky machines to maintain.