SOMO finished with AR

[jofelk]

Has anyone else tried the SOMO finished SV leneses with AR cote?

I am a little concerned because the center thickness on the low minus Rx is 1.2 -1.7 thick, and the higher minus is 1.5-1.8.

They did not pass my drop ball test. SOMO insists they pass their batch test method so we are not responsible.

This is the first time I encountered finished lenses this thin.

[Pete Hanlin]

Depending upon the material you are speaking of, the 1.2 - 1.8 may not be unusual (although usually the lower minus powers are left a little thicker to prevent flexure). Even CR-39 can be ground thin given the proper coating. For example, there is a thin version of the FSV CR-39 Crizal product.

Regarding drop ball testing, you are wise to conduct a sampling of the lenses you produce (since this is required by the FDA). Also, regardless of any assurance you may have from your supplier, you are ultimately responsible for the impact resistance of the lenses you "manufacture" (if you are edging the lenses, you are considered the manufacturer by the FDA).

[Chris Ryser]

jofelk said:
Has anyone else tried the SOMO finished SV leneses with AR cote?

I am a little concerned because the center thickness on the low minus Rx is 1.2 -1.7 thick, and the higher minus is 1.5-1.8.

They did not pass my drop ball test. SOMO insists they pass their batch test method so we are not responsible.

This is the first time I encountered finished lenses this thin.

It is a known fact that many AR coated lenses do NOT pass the drop ball test due to the characteristic changes of the lens material composition during the AR coating process.

[jofelk]

Pete Hanlin Depending upon the material you are speaking of, the 1.2 - 1.8 may not be unusual (although usually the lower minus powers are left a little thicker to prevent flexure). Even CR-39 can be ground thin given the proper coating. For example, there is a thin version of the FSV CR-39 Crizal product.

The lenses are CR-39. We will be returning our stock. We do not want to distribute a lense that "MAY" cause injury.

[Pete Hanlin]

Good decision- especially if you are not equipped to do extensive impact testing.

I do not know that I would use the term many regarding AR coated lenses that fail the FDA referee test for impact resistance (drop ball). A lot depends upon the lens material, the underlying scratch coating, the AR stack, and the manufacturer. It is definitely possible to create an AR coated lens that will fail the test, but responsible manufacturers of lenses (and AR) test the product quite extensively (I know Essilor does) and will not sell a product with impact resistance issues.

This does open the door to an interesting discussion. There are growing numbers of lenses made by smaller lens manufacturers in emerging markets (especially Asia) being shipped to the US. These manufacturers may or may not extensively test to ensure FDA compliance (indeed, they may not be completely aware of FDA standards). I've worked with some of these lenses as a dispenser, and have seen them at the shows. Sometimes the quality is acceptable- sometimes the lenses are unacceptable.

[Jim Schafer]

In order to clear customs all lens products coming into the US must have FDA papers showing that lot passed impact testing.

Depending on the size of the lot (SOMO batch size, that Jofelk refered to) you are allowed a certain amount of failures. It may be interesting if they have to disclose how many failed or if the documentation only lists pass/fail per lot.

I believe the FDA paperwork has to be available for 2 to 3 years.
best regards,
Jim

[Pete Hanlin]

Customs is an interesting jungle... I've seen product held up for really odd, nitpicky reasons- and we've found products that shouldn't have been allowed through that flew right on in. Also, if AR coating is being added to the lenses after they are shipped to the US, the supplier may or may not have conducted any tests to see if the lenses will be compliant after the coating is applied. This is the responsibility of the coater (or, if the coater does not test, the lab that has sent the lenses in for coating).

[Chris Ryser]

Pete Hanlin said:

...............the supplier may or may not have conducted any tests to see if the lenses will be compliant after the coating is applied. This is the responsibility of the coater (or, if the coater does not test, the lab that has sent the lenses in for coating).

1)
Do you make a drop ball test on every lens after it has passed the coating process?

2)
Are your competitors doing this too?

3)
What is the drop ball test doing to freshly done AR coating?

[Pete Hanlin]

Do you make a drop ball test on every lens after it has passed the coating process?
As you know, Title 21, Code of Federal Regulations, 801.401 states that all monolithic (non-laminated) glass lenses shall be treated to be impact resistant. An amendment in 1979 (44 FR 20676) mandated a test equivalent or superior to the drop-ball (referee test), and described specific prescription lenses that must be impact resistant.

Assuming we are discussing the testing of non-mineral (glass) lenses, there is no requirement that every lens be tested. However, according to FDA 29 CFR 801.410(d)(2)- the manufacturer shall subject to an impact test a statistically significant sampling of lenses from each production batch, and the lenses so tested shall be representative of the finished forms as worn by the wearer, including finished forms that are of minimal lens thickness.

Therefore, the requirement is to test a sampling from each batch. Determining what constitutes a "statistically significant" sample is determined by ANSI/ASQC Z1.4-1993 (Sampling Procedures and Tables).

Essilor meets/exceeds the requirements of the FDA standards via a series of validations. Before a product is launched, it will be impact tested with a variety of SRC/ARC configurations using a "critical SKU." The "critical SKU" is a base curve, ADD, and Rx which yields the thinnest overall lens. Although previous experience gives good indications regarding which SRC/ARC will yield the lowest impact resistance, several are tested to confirm a "worst case scenario." Then, lenses are fabricated to these specifications (critical SKU with the worst possible combination of SRC/ARC) and undergo drop ball testing to ensure they will pass.

Once the product has been validated, processing recommendations are created and each lens arrives in a packet stating that- when processed according to the recommendations provided by Essilor- lenses have been batch tested to ensure conformity to the FDA impact resistance standards. However, the final manufacturer of the lenses- which is the laboratory fitting the lenses into finished eyewear- is also responsible to batch test the finished form of the lenses it produces (including some lenses that have been AR coated).

Are your competitors doing this too?
I cannot speak to the practices of competitors since I have not observed them; however, I would assume that all of your major lens manufacturers have a very well documented system similar to ours.

What is the drop ball test doing to freshly done AR coating?
Regarding the coating, I doubt there is much impact (pun intended). However, since the test will flex the lens it is conceivable that there may be micro-fractures in the coating (since most lens materials are more pliable than the typical AR stack. In general drop ball testing makes a lens less impact resistant (e.g., if you drop ball test a glass lens over and over, it may eventually fail).

[Chris Ryser]

Pete,

Thanks for the excellent response, I hope it is read by many of the Optiboard members.

However I could use one more answer,

If I understand correctly, by buying ESSILOR lenses and would AR coat them I would be resonably sure that they would all pass the drop ball test after coating?

Thanks

[Pete Hanlin]

If I understand correctly, by buying ESSILOR lenses and would AR coat them I would be resonably sure that they would all pass the drop ball test after coating?

Affirmative- unless you are planning on doing something quite radical and unexpected with the product (e.g., purchasing AR coated product, stripping the AR coating, and re-AR coating with a different process), you should be able to use Essilor with confidence that your process has been validated.

Typically, we test all the configurations that will be produced by Essilor and ELOA, plus several additional backside coatings and ARCs that will be used by customers. Validation can be a really tedious process (one of the more tedious in my job, anyway), but it is definitely interesting- and sometimes even a little surprising.

Beyond impact resistance, Essilor also validates other features of the product to ensure product quality, consistency, and processibility (called "capability") in real laboratory environments. You'll forgive me- hopefully- for going on a bit here- but it really is something to see the Quality R&D people at work with their equipment, clip boards, etc.! Every company makes some bad product, but I can say with a lot of confidence that there is a team of individuals (of which I am a small part) dedicated to ensuring that defective product is the very rare exception at Essilor.

:D