Please help with AR coating and heat.

[matmal]

I know this has been discussed and that heat will cause ar coating to craze due to lens expansion, however I have a customer who is really concerned about his new glasses which have 1.67 lenses with -2.50 cylinder and Teflon ar on them because they were adjusted by another store and placed in hot water to bend the bridge. Now the lenses still look fine, but he is worried about long term effects showing up, and I really didn't know what to tell him.

So my question is just that, if hi index lenses with ar on them are placed in hot water will it always cause damage even if not at first? Thanks all.

[newguyaroundhere]

Could the lens craze? Possibly. It would depend on a number of factors such as the brand of anti glare, how the hard coating was applied (spin coat versus dip coat), the actual Rx of the lenses, how the lenses were edged into the frame, how the patient takes care of them, etc

[Uncle Fester]

Welcome to Optiboard matmal!

Some time ago the magic number of 130 degrees (54.4C) was put in my head as the temperature not to be exceeded for AR. So if true I doubt hot tap water would affect the AR. I would also assume if it did, the crazing would occur quite soon after any catalyst. That said I've always found 1.67 to be one of the most sensitive to crazing and try to avoid it for that reason. But that may be just me. I believe you have a 2 year warranty with Teflon (w/ a $15 s+h fee!) so I'd tell the patient to keep that in mind. Lens power doesn't matter.

Cheers!!!

[Tallboy]

It will show up fast if it happens. Now if the lenses are too long in the A measurement for the frame, it is possible that contraction of the frame in cold air may craze them down the line (if thin center minus). But hot water (or heat in general) just expands the lens material and the AR, if the Lens expands or contracts faster than the AR can expand/contract the AR will crack like dry mud in a desert.

There is no damage done if there is no visible damage for you to see, however crazing can be a ***** to see sometimes... Its not like the heat wears away layers of the coating or something.

[tdj]

Would there be any harm in warrantying them out for pt's peace of mind?

Frankly I'd give the pt a gentle ribbing for taking them to anyone but me ;) and then warranty the lenses to make him feel better.

[DanLiv]

It will show up fast if it happens.

There is no damage done if there is no visible damage for you to see, however crazing can be a ***** to see sometimes... Its not like the heat wears away layers of the coating or something.

+1. Crazing isn't a gradual process, they are either crazed or they aren't, and if they aren't it won't show up later (from that incident). Have you ever seen a single crack line of crazing? I haven't. If it's crazed it's a big deal (though sometimes hard to see, true, but we should always be able to find it). There is a threshold of stress/temperature below which there will be no damage, over which there will be considerable damage.

[mervinek]

I've never heard of adjusting frames with hot water...although I worked at National Vision in AZ (years ago when I went to ASU) and they used to dip their glasses in a bowl of Mister Clean to clean the lenses. That was regardless of material. Interesting things some offices do.

[Chris Ryser]

Now the lenses still look fine, but he is worried about long term effects showing up, and I really didn't know what to tell him.

So my question is just that, if hi index lenses with ar on them are placed in hot water will it always cause damage even if not at first? Thanks all.

All AR coating are made with the same material, SIO2 which is glass, with some added oxides for coloring.

The main difference is the coating between the lens surface and the AR coating, that makes the AR coating adhere to a plastic surface. There is no need for that coating if glass lenses are used, as the SIO2 bonds well with the glass surface.

In extreme heat or cold a plastic lens can expand or contract and will craze as the glass AR layer has not the same coefficient to expand or contract.

[Dpareynolds]

All AR coating are made with the same material, SIO2 which is glass, with some added oxides for coloring.

The main difference is the coating between the lens surface and the AR coating, that makes the AR coating adhere to a plastic surface. There is no need for that coating if glass lenses are used, as the SIO2 bonds well with the glass surface.







In extreme heat or cold a plastic lens can expand or contract and will craze as the glass AR layer has not the same coefficient to expand or contract.

Crazing, what a problem! My experience, which is considerable (30+), has been transitions Crizal Avance' craze, transitions 1.67 a/r craze the most. I would even state that Transitions 1.67 A/R will always craze given enough time. The A too long, the lens a tiny big, all contribute. A titanium frame with the lens a tiny big causes eventual crazing, usually after 2 years. My personal experience is ALL my transitions pairs of glasses eventually craze, not true with cr39 or poly. I've complained to the Essilor rep as I am a predominantly Essilor Crizal store, but to no avail.
Has anyone had enough experience with other photochromic resin lenses such "Photofusion"? I've had poor experiences with "Life" photochromics in my industrial program. Haven't used "Sunsensors" for years, availablility in a good progressive is it's limitations. Curious if Photofusion has the same problem as Transitions with crazing.
Hardcoat flow or rippling is another transitions problem my customers have had. Chris, any thoughts about the type of hard coat most likely to heat ripple would be appreciated.

[Robert Martellaro]

Some time ago the magic number of 130 degrees (54.4C) was put in my head as the temperature not to be exceeded for AR. So if true I doubt hot tap water would affect the AR.

Walman told me 120 degrees. Colts has probably tested for heat damage, but I don't have that data. I have seen modern coated ophthalmic lenses fail due to exposure to heat when left inside of an automobile where the outdoor temperature was above 90 degrees.

http://ggweather.com/heat/heat%20study.pdf

[Chris Ryser]

Crazing of AR coatings, then mostly used in Europe, has never been a problem, because you put a layer of glass onto glass, and they both have the same expansion or contraction coefficient.

However in the age of plastics and the many different plastic materials used to make lenses, there is the need to use an intermediate coating that acts as an adherent for the glass AR coating (SIO2) and the basic plastic lens material.

Now you have the basic lens material, the in between coating and the final top coating, and all of them act different in extreme temperatures from cold to hot, so crazing and delamination is a natural thing to occur in countries that have weather extremes as North America.

People will walk into a warm heated building from extreme cold or into the humid heat from air conditioned interiors , and the glasses will fog up, and are ripped of the face with one hand creating an immense pressure on the frame that can start a crazing and delamination effect on the lens coating.

In most cases this should not be a warranty issue, but a missing out of proper education by the optician or optical sale people. Also the simple use of a good AntiFog product could help to prevent some of these cases.

[Robert Martellaro]

So my question is just that, if hi index lenses with ar on them are placed in hot water will it always cause damage even if not at first?

It depends on the temperature of the water. Typical hot water at the tap is 120 degrees or less, so I would guess that short exposure times would be safe, although it's a stupid thing to do because most frame plastics need higher heat to modify the shape safely and effectively than what we'll find from the hot water tap.

Now you have the basic lens material, the in between coating and the final top coating, and all of them act different in extreme temperatures from cold to hot, so crazing and delamination is a natural thing to occur in countries that have weather extremes as North America.

Casual observations tell me that's not the case (not that North America is a country), that is, that modern ophthalmic coatings "naturally" craze when exposed to indoor/outdoor temperature swings. It would be easy enough to check though by comparing failure rates from one brand of AR from a Seattle lab and a Minneapolis lab, both sold to local practitioners.

However, the coating manufacturers do warn us that temperatures that can easily be achieved inside of an automobile on a hot day (with the windows closed) will most definitely weaken/degrade/destroy modern ophthalmic AR coatings.

[Robert Martellaro]

Old, but relevant.

http://www.gef.es/congresos/27/pdf/8..pdf

[Java99]

In my experience, when ar lenses are left in a hot car, one will see an orange peel effect on the lenses. When they craze, it's usually due to adjusting or glazing with too much heat OR flexing of the lens, or a lens cut a smidge too big. I wash my personal lenses in very warm water from the tap almost every day since about 1998, no issues with any brand of ar in that time.