Manufacturing Errors Commonly Overlooked In Eyeglasses & Lenses

by admin on 12/03/2010


There is nothing worse than finding out that a pair of eyewear was dispensed not up to par.  As an Optician, there have been
countless times where eyewear has been brought to me and low and behold, errors in the manufacturing.  These errors can be made on the frames themselves or on the lenses, and for the most part the lenses errors are most detrimental to the patients overall vision.  Below are listed some of the things that I have found while working as an Optician that really got under my skin, so as you study toward becoming an Optician, certified or licensed, remember that it is all about fine detail sometimes only seen with the trained eye.

LENS MANUFACTURING ERRORS

Scratches, scratches and more scratches – Okay so there really isn’t any need to define what a scratch is because it is pretty much self explanatory.  During the manufacturing process or even during dispensing, things happen, and when things happen, scratches on a freshly made pair of eyewear can happen, too.  The key is to not allow it to take place and I will have some pointers about how to do this in another post very soon.

Whenever one is inspecting a pair of eyewear in the laboratory, prior to the finishing process of edging  and even after edging and cleaning, it is crucial to inspect for scratches fine or just plain blatant.  Reason being is because these scratches have the potential to interfere with vision or in the least worrisome of cases, just make the highly expensive pair of eyewear look tacky.  This isn’t great customer service.  Therefore search under a lamp for those common irksome scratches.

Prefabrication Swirl  Marks

Oh to damnation with these swirl marks, and it is a wonder how on earth swirl marks even get by undetected before leaving the laboratory.  Anyway, lenses must go through a process on the cylinder machine after the lens has the prescription cut or “generated” into it.  The reason for this is because the generator, which is the machine used to grind in the prescription, leaves highly defined marks in the lens, so much so that it isn’t see through.  Therefore, in order to begin the process of clearing the lens, one must use the cylinder machine.

So the swirl marks are fine circles, like circular scribble marks,  all over the lenses or in a particular area which will impair the patient’s vision.  These marks can be overlooked if not paying attention or holding the lenses up to the light for inspection after polishing.  Polishing is the final step in clearing the lens.

Pits

Okay, pits are only going to occur in polycarbonate lenses.  Why? Because plastic lenses don’t require what is called a coating.  Without a coating on polycarbonate lenses, scratches will occur extremely easily.  However, along with coating application, another issue could result harming the overall readiness of the lens and that is the formation of what is known as a pit.

Pits are small bubbles on the back surface of the lens.  Imagine a sink full of water and one very small bubble floating around in it, except for on a lens, it doesn’t float but is stagnant and hard.  This bubble, or pit, is totally not supposed to be present on on finished lenses, and if detected, will cause the entire pair to not meet quality standards.Wrong Prescription

Chips

Surprisingly enough, chips do get pass inspection to the final pair of eyewear, and many times it is by pure accident upon mounting, or putting the lenses securely inside the frame.  The chips occur on the edges of the finished lens, and sometimes, chips can even be hidden with the frame’s rim, therefore, it is always important to check for a chip due to the fact that it can eventually spread into a crack across the entire lens.

Wrong prescription

This type of error is self explanatory.  When neutralizing or reading a prescription in lenses with a lensmeter, automatic or manual, by ANSI standards, only a certain very small percentage of err is to be overlooked.  If it goes over the documented ANSI standard, the eyewear must be rejected and the lenses re-cut.

Loose lens fit

Upon final inspection of mounted eyewear, the fit of the lens to the frame but be extremely snug so that the eyewear will no move while mounted.  Movement of lenses in eyewear will cause it to go off axis, thus, changing the overall prescription.  The higher or more powerful the prescription, the less the axis can be moved.

Gaps in eyewear

Sometimes one will find what is called and looks like gaps in eyewear, that is because this is really what they are – gaps.  There should be no gaps, or openings big or minute between the lens and the frame at any point.  This means at the screws or around the rim.

Uneven Bevel

Bevels are placed on lens during the fabrication process of edging using a machine called an edger, and also a different type of bevel is put on the back of a lens to avoid scratching the patient’s face.  This other bevel called a safety bevel is done using the manual edger, or hand stone.  When safety beveling a lens with the manual edger or hand stone, the bevel is supposed to be even all the way around the lens and not too thick, barely noticeable.  If the safety bevel is uneven, this is a rejected lens.

The other bevel done on the automatic edger is used to create a secure hold for the lenses in frames.  Care should be taken in placement of this bevel as prescription and type of frame need to be first considered before beginning the process.  A bevel placed in the wrong area on the lens can result in a lens that continues to pop out of the frame.

Waves

This type of wave isn’t the hello, bye-bye one.  Instead it is the type of wave that can appear in the finishing product of a lens during the prefabrication, or first stages in making the prescription.  If a lens is overheated, through the generating process or cylinder machine process, a wave will be formed.  This wave will alter the patient’s vision if dispensed, therefore, care should be taken in locating waves.

glasses

Improper markings and blocking

This is the final error I will speak of though there are more.  If a lens is improperly marked or blocked, then the entire finished product will be canned.  The marking and blocking errors can occur during the start or finish of a pair of lenses.  Markings and blocking in the beginning will result in off axis errors, prism etc.  Marking and blocking errors at the finish will result in pupillary distance errors, mounting issues etc.  Therefore, when these type of errors occur, they are normally caught before dispensing.  If not, the patient will automatically notice that something is terribly wrong.

Very soon I will take this list of things and go into a how to prevent these issues in the laboratory section.

{ 2 comments… read them below or add one }

Josh June 12, 2011 at 16:36

I have had to replace one pair of lenses of my current pair of lenses due to swirl marks appearing in the center. The replacements are now starting to develop them too. I haven’t had this happen to any other pair I’ve ever owned. I’m starting to think the materials used are not what I paid for.

Though I do use dish soap and water as I find it does the best job of cleaning off smudges and reduces glare (except for the swirls). Perhaps I’m cleaning off the polishing that was hiding the marks in the first place. But like I said, I’ve always used the dish soap and water method for all my prescription lenses with no problems.

admin June 17, 2011 at 07:48

Real swirl marks come from lens manufacture and shouldn’t ever be there. Swirl marks don’t come from cleaning the lenses, scratches may come from frequent cleaning but swirl marks don’t. Therefore, if you feel you are definitely seeing swirl marks, visit the eyewear facility that you purchased them from and be sure that an Optician in the lab or retail looks at the lens thoroughly. If swirl marks are found, the lenses should not have passed quality inspection, therefore must be redone.

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