I was wondering if any of you would consider not decentering high plus lenses to get a better cosmetic effect.
I realise the prismatic effect introduced is a factor but consider the horizontal vergence tolerance to be very high much higher than the vertical which we most often ignore when considering decentration.
Many people get on perfectly well with ready readers in high plus powers.
many thanks
Why not take few diopters off...that'll thin it down a little!
not a very helpful answer,probably why you are in the job you are in.
"readers" are not actually sold as a "corrective" lens as we have to do so what we do falls under the ansi standard..which means we have a 1 mm area to play in on the PD and 1/3 of a diopter of induced prism.. so it is a NO-NO to do it "legally"
BTW a surfaced high plus is not going to be all that thick be it done using prism rings for decentration or without when you cut it you surface it to fit the given measurments of the frame, now if you try to use a "stock" lens than you will end up with a brick..since the thinnest point is at the edge of the finished blank and taking nothing into account for frame size :)
I still argue nack in forth with the accounts about "oh this lens is to thick" but on the invoice they REQUESTED finsihed stock blanks.. go figure
As long as you do not mind taking a chance of losing everything if you get your pants sued off by tossing out the ansi standard, I say go ahead and do it :) I just always figured that is why we should be here to do it CORRECTLY..if not than just everyone should just stock readers :)
Jeff "grind'em and they will come" Trail
(just a little Fri. night movie refrernce..sort of) :)
Absolutely not. I'd adhere to the ANSI tolerances at a minimum. If you want better cosmetics, then choose a more appropriate frame for the Rx.pete said:
I was wondering if any of you would consider not decentering high plus lenses to get a better cosmetic effect.
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decentration
Pete, one should always dispense glases with the correct pd. In the case of readers, which can be plus or minus depending on the distance rx verses the add power, the first secret is in the frame selection.
.....First you should accurately measure the near pd. Next you can try and select a frame that has the same pd as the patients near pd. This by itself eliminates any need to decenter.
.....Your next concern should be the size of the frame and the shape. frames with long "B" measurements, or frames with long ED,s should not be chosen unless necessary or patient preference.
.....A reading glass does not have to be large at all to function well as a reader, remember a patient sees out of the pupil, which on average is usually no more then 5 to 7 mm.
.....In the case of plus lenses wire or metal frames will both work well. In the case of a reader that is minus in power a plastic frame will often look better as the plastic will tend to hide the edges of the lenses better.
.....On a more cosmetic note for optimum thinness and looks you may want to consider a high index aspheric lens. If you have one of those high minus readers you may want to consider a high index atoric lens for optimum thinness, and use AR coating.
Um guys ... you are assuming that pete is from the United States. If he wasn't, he wouldn't necessarily have standards from the American National Standards Institute (ANSI) to follow.(hint)
John R, you may want to field this answer so that pete is getting information that is pertinent to his National standards.
Sure. I'd pick a roundish frame that allows the horizontal and vertical oc's to sit on center. Not an once of decentration to be found.pete said:
I was wondering if any of you would consider not decentering high plus lenses to get a better cosmetic effect.
Oh, you mean run the oc wide to thin the nasal? Maybe because the client wanted a frame style that was going to be a nightmare to fit? Not if you don't mind re-making the lenses a couple times (ouch) when the client complains of strain and headaches, with the end point being what you should have done in the first place, which is practicing good opticianry. If you are the curious type like me, make yourself a pair of glasses with two or three prism diopters base out in each eye. Works best when performing near tasks. ;)
Robert
Well if in Uk then they are pretty much the same as State side apart from we allow nice thin minus powers....but that doesn't come into play here.Jo said:
John R, you may want to field this answer so that pete is getting information that is pertinent to his National standards.
As others have said find a frame that causes the least amount of decentration to be worked. Do you really want to have patients that cant see properly.
I was wondering if any of you would consider not decentering high plus lenses to get a better cosmetic effect.
Pete,
I looked at your profile and it does not say anything on your profession, so I assume that you are part of this profession.
The optical retail trade is supposed to be a profession where quality is the most important item and on top of the list.
If you would not have to care about decentration and other technical aspects the optical retail trade would be a dead issue and everybody could order their glasses at a mail order house or buy them at the flea markets.
The fact of the matter is that horizontal centration is less important than vertical centration and truthfully how many of you take that measurement.
What about amblyopic eyes? what are you doing for the good eye ,always place optical centre before pupil.WHY?
If you argue the best image quality is obtained with oc at pupil do you then never achieve prism by decentration.
The way you have answered you would think that every px ye dispense over+3.00 was found a frame which required no decentration and a=b.Sorry it does not happen
.Sometimes a px will want to use old frame which requires large blank size and we have all had thick jobs back from labs which we have been disappointed with usually due to using stock blanks when you have requested mbs and indeed charging for surfacing.
Incidentally some of the eyewear that i see Americans coming into my store in the UK is appaling ,politicians, tv presenters with no ar coats.,regular people moderately myopic wearing cr39 the lowest index available,so much for good opticianry.I have even tested one of your senate and he is now on his third pair of 1.9 Zeiss.,try getting them in your great land. Thankfully we still live in a England. I was only trying to play devils advocate to brighten up an increasingly dull optiboard and all i get is sanctamonious pie.I was hoping for some technical and stimulating debate not Uncle Sam told me to take pd at optometry school and i take it on every px .I bet half of you dont know why you take it and take it everytime even for aspherics instead of mpds.By the way to the chap who wondered what i was i am an optometrist and proud of it.Is that the same chap who was advocating castor oil for recurren conjunctivitis.Now that is truly litigious never mind not taking a mpd on an amblyopic px
pete,
With the exception of possibly one reply, folks were trying to be helpful. They were trying to anwer your question the way they interpreted it as being asked. Some folks didn't know that you were from the UK so they answered your question using ANSI standards. No one challenged optics from abroad.
After your coarse reply, I am sorry I tried to help out myself.
By the way to the chap who wondered what i was i am an optometrist and proud of it.Is that the same chap who was advocating castor oil for recurren conjunctivitis.
By the way the printout on castor oil came out of a UK textbook. Glad you do take the PD as you have been taught.
As you are under the impression the Optiboard is boring, why did you try to pull everybodies leg? You could have started an argument on slighly higher level to make the discussion interesting and lively.
There have been many good discussions over the last few month and I dont think that everybody on this side of the atlantic has to be stupid in the optical trade.
I still remember a time when at the old Northampton Polytechnicum school of optics was not even a lensometer in use and all lenses had to be neutralized by hand. When the first instrument was introduced nobody could even use it while over all of Europe every optician had been using them for years.
So now we know, even the English learned. They have progressed form the old national health frames that everybody had been wearing for years to modern times.
I don't think that it is fair to say that everything that comes from across the atlantic to the UK looks appalling. You for sure have some backwood opticians, and or optometrists, as well as every other country has, but you should not gerneralize and single out the North Americans.
So the ball is back in your front yard and you can continue a lively discussion on the Optiboard.
Sadly the americans think that thin glass is something best not worn in front of the eyes...pete said:
.I have even tested one of your senate and he is now on his third pair of 1.9 Zeiss.,try getting them in your great land. Thankfully we still live in a England.
Maybe you would like to shame and name the senator so some of this board can take him to task over this issue....I know plenty of americans who would love to wear thin glass but cant get it state side...
Maybe we could set up and supply them :) but sadly even thats against their laws.....
Whats good for the goose is good for the gander..
There was a lab in Fla. sometime ago that was making alpkaic lenses for polymils(rememberthose?) . My coustomers would ask Why you can't get them as thin as these? Those a$$ holes were not decentering them just to make them thinner. Now we got two problems. Patients had gotten used to 5 diopters base out. Dang, can you imagine? If you ask for this way of thinning down lenses, you need to give up your lisenses. :angry:
John,John R said:
Sadly the americans think that thin glass is something best not worn in front of the eyes...
What is the preferred method for tempering thin glass? Bob Rihl once told me a story about putting a pair of B&L thin glass lenses in an ultrasonic cleaner only to pull them out with two holes worn right through the middle. I've seen folks in accidents shatter Crown and PGX ground to 2.0 and chem tempered, albeit they were somewhat freak accidents.
Ourt of curiosity, what standards do you follow in regards to Rxs? I'm particularly interested in knowing if you have tolerances for PD and unwanted prism.pete said:
The fact of the matter is that horizontal centration is less important than vertical centration and truthfully how many of you take that measurement.
What about amblyopic eyes? what are you doing for the good eye ,always place optical centre before pupil.WHY?
Not the same thing. If there is prescribed prism then it's not inappropriate to achieve this prism by decentration instead of directly grinding it. The result is the same.If you argue the best image quality is obtained with oc at pupil do you then never achieve prism by decentration.
In the end, isn't it our responsibility to match the Rx as closely as we can?
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decentration
Pete, i guess i will also have to apologize for trying to be helpful, just for your information ZEISS 1.9 glass is available here in the states as well as 1.8 thinlite. Reason we dont dispense much of this here in the states are twofold, one you have to get a doc to sign off thats its ok and the other is we have lawyers who would make a fortune if one of these lenses broke and did permanent damage.
.....I think if your as bright as you pretend, you need to take a course in basic manners, and get rid of that bloody attitude as you do not fit in here well with all the other brits, who certainly are more polite.
I think that in the US there are too many lawyers who twist safety perceptions so they can make more money. Obviously it's not done completely altruistically.
I read stories on a daily basis about lawsuits in the states that are just so absolutely absurd it makes me shudder.
Even in Canada if a burglar trips in your house when he's breaking in, he can sue you...and win. WTF!
More lawyers equals less fun. That's the simple equation.
In this particular line of work it impacts the cosmetic parameters of a lens and in the food industry it impacts absolutely everything far more. Don't get me started on that because I put in 15 years and I can honestly say that some of the best meals I've ever eaten have been in countries our health departments would have shut down.
I'll sign off before going way off topic.
Maybe so. If I ever get screwed buy one of you guys, having "fun" "so they can make more money" , bet your 15 years of meals I'll have my day in court. Glad you are, and hope you stay TF! in Canada.
edKENdance said:
I think that in the US there are too many lawyers who twist safety perceptions so they can make more money. Obviously it's not done completely altruistically.
I read stories on a daily basis about lawsuits in the states that are just so absolutely absurd it makes me shudder.
Even in Canada if a burglar trips in your house when he's breaking in, he can sue you...and win. WTF!
More lawyers equals less fun. That's the simple equation.
In this particular line of work it impacts the cosmetic parameters of a lens and in the food industry it impacts absolutely everything far more. Don't get me started on that because I put in 15 years and I can honestly say that some of the best meals I've ever eaten have been in countries our health departments would have shut down.
I'll sign off before going way off topic.
Perhaps you misconstrued my post Jim. I was not stating that it was ok to decenter to your hearts content to make lenses thinner. I was only pointing out that safety legislation in regards to minimum ct were due to the litigious nature of the US.
A little harsh in your reply man.
Last edited by edKENdance; 07-19-2003 at 09:38 PM.
Perhaps, sir. But I think you missunderstood my reply. I took serious offense at your ludicrous implication that the legal system in canada is somehow different, in a possitive way to the US's. KMA
My appoligies for being harsh.
Jim, I definately don't think that the Canadian system is better but as a stat, you have 10 times the population then we do so I hear about 10 times more stories out of the states then I do from canada. It's all about perception in that respect.
I think the thread starter has turned this into an interesting thread after all. And I thought I needed a life:)
Im editing this post because somewhere along the line I notice that the UK has no problem with a thinner ct.
There must be an ansi website that lists all the untimely incedents caused by minimum ct sans hardening or else we will all die a smokers death(only at the ridicule of others)
Last edited by edKENdance; 07-19-2003 at 09:56 PM.
If you really want to play this foolish game and the tolerance is 1/3 diopter. You can de-center a +or- 1 diopter lens 3.3 mm. You can decenter a 10 diopter lens .33 mm. So you can see with a high plus or minus lens there really isn't much to play with. Patient's will probably tolerate .5 to .75 horizontal prism but, tain't legal Magee!
Chip
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