# Optical Forums > General Optics and Eyecare Discussion Forum >  Decentration

## April_01

Ok, this is a stupid question for someone who is aboc, but could somwone explain to me what exactly decentraction is and how to do it? I know I remember reading about it when studying for my abo and it has to do something with pt's pd and frame but I never really understood it and from the forums it sounds really important that I should be doing this.:hammer:

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## Lab Rep

April I hope this helps.

Your patient has a specific PD both at a distance and near.  This distance, as you know is best measured by using a pupilometer.  The frame that your patient has chosen also has a PD.  The frame PD is measured by adding the eye size to the bridge size.  Decentration is simply a big word that means how far do we have to move the optical center of the lens, in or out, when blocking, to be directly in front of the pupil when the lens is mounted in the frame.  If our optical center is not directly placed in front of the pupil we will create unwanted prism.  Also the less decentration that we have the thinner we can make the lens.  A 1.60 index lens can actually be thicker than a cr-39 of the same power due to poor frame selection or more decentration.
The formula is Frame PD- Patient PD / 2= Decentration each eye.

Example:  Patient PD 68.  Frame 50/20.  
Frame PD = 70
Patient PD= 68
Decentration = 1m/m each.

I hope this helps.

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## Chris Ryser

> *Ok, this is a stupid question for someone who is aboc, but could somwone explain to me what exactly decentraction is and how to do it? I know I remember reading about it when studying for my abo and it has to do something with pt's pd and frame but I never really understood it and from the forums it sounds really important that I should be doing this.:hammer:*


Someone who is aboc ? Does that mean American Board of Opticians Certified ?
If that is the case I would like to hear from other aboc members how they could pass the exam without knowing the answer to this basic question. :finger:

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## impact500

Chris it is impressive how often you are a genius and others are idiots. April does not know something. She can either ask for help or try to hide her lack of knowledge. Which is better? And other readers can either help her or make fun of her. Which is better?

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## Joann Raytar

Impact is right.  It isn't very nice to take jabs at someone asking questions and trying to learn or refresh their knowledge.

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## Jedi

Sorry, I fail to see how Chris was making fun or taking jabs at April. She herself said, "I never really understood it". I think what Chris was getting at was, how can the Board allow someone to pass when they do not understand a concept that is used on a daily basis.

We whine and moan about OD's, MD's and the public not being aware or supportive  of what we do, we kick and scream to increase our scope of practice. But we can't ensure that students taking their exams are clear on all the concepts.

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## Texas Ranger

APRIL_01. Ahhhh!  April fool...

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## drk

You guys are harsh. I know lots of people who can memorize a formula for a test and do well, but not have a firm enough concept to keep it in the memory banks long-term. Happens all the time. I'm SURE that there are formulae that you once could regurgitate, plug-and-chug, and now have forgotten. I know it's true for me.

Are we getting spoofed with April 01?

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## April_01

Thank you to those who actually helped with my question. I am sorry that I am such an idiot that I did not know answer to that question (that I now am under the understanding is really easy and everyone should know after taking the test last year) but I have studied hard prior, during, and after the exam to keep my knowledge up. I really have a hard time remembering EVERYTHING on optics everyday all the time. That is why I have been interested in this forum.If you all know some secret I would love to hear it, I thought that was why we were hear to discuss things you didn't know. If I am wrong about this and you are supposed to be doctors, lab techs, or geniuses, then let me know and I won't bother you all with my trivial questions. Again, I am sorry if I am concidered an idiot, but I really wanted to know. Haven't any of you had a question that was supposed to be basic knowledge?

P.S. I also think for an idiot I did pretty good considering the night before I had to take the test, I found out my grandmother had died, had no sleep, took the exam, and passed. It wasn't a perfect score but it was above average in all the areas. I am proud to have passed and no matter what you all say or think of me, I am proud of what I have accomplished and will only continue to work harder.

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## Jedi

I don't see any posts that called you an idiot. My apologies if you took offense to my post. I feel that if instructors and admininstrators have students leaving a course not understanding basic concepts they are not doing their jobs and are letting the students, employers , and the public down.

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## mrba

> Impact is right. It isn't very nice to take jabs at someone asking questions and trying to learn or refresh their knowledge.


.....

I think Chip's jab was more at the ABO. And I think it was well deserved.

I don't think most people stop to think how much poor measuring and issues with figuring problem Rx's really cost this industry. Millions!

As far as April 1st goes, you keep asking dumb questions.  It is the only way to not be dumb!:idea:

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## Chris Ryser

> *Impact is right. It isn't very nice to take jabs at someone asking questions and trying to learn or refresh their knowledge.*


If the question would have come from somebody outside the optical retail industry, it should have, and would have been answered even by me.

How many more are there out there in the field not knowing the basics????? To me that is frightening.

How confortable would you be to purchase a pair of $ 380.00 or more, glasses from  opticians, knowing that they do not even know how to apply the basic rules of the profession.

Next time you go to your dentist better make sure he knows where to drill tha the holes or when your car mechanic asks you what the wheels on your car are used for.

*I knew that most of you were going to fall all over me for speaking up in the way I did*. 

I don't agree that a question, of which the answer can easily be found in any of the textbooks of any profession, and in any language around the globe should even be answered.

This is a public forum where anybody can look in from the outside and if someone pulls a joke, it should be recognized and treated as such.

:finger:

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## April_01

Ok Chris, first off, this is not a joke and I am sorry if that is what you thought. My name stands for my first name and the year I entered the field not April Fools.I am not mad at you for giving your opinion because it is true, that is why I stated it in my first post and I knew I would get a lot of **** about it. I should have be a little more specific on what I was actually questioning though. I knew the basic definition of decentration but I was not sure how to calculate it(our computers automatically calculate for each eye) or how much decentration would be too much and make the lenses thick. I could have looked up the formula in a book but I thought I would ask the forum (which was a mistake). I wasn't sure how high the number had to be to were it would not make a difference in lens materials thickness,but then again this is one of those questions you would need specifics to compare to. Also, on some of the posts people talked about decentering optical centers for cosmetic purposes and not using decentration. Is this acceptable?

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## mlm

> I don't agree that a question, of which the answer can easily be found in any of the textbooks of any profession, and in any language around the globe should even be answered.


But there are tons of questions asked in this forum that can be answered through textbooks, articles, catalogues and whatever other paperwork we have at our disposal. The point is that the question was asked, and it deserved an answer.

It takes a lot to admit that you don't know the answer to a basic question. I would like to hope that if anyone had a similar type of question, they could feel free to benefit from all our combined knowledge rather than remain silent for fear of ridicule.

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## mrba

> I would like to hope that if anyone had a similar type of question, they could feel free to benefit from all our combined knowledge rather than remain silent for fear of ridicule.


or a textbook that is difficult to understand.

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## JRS

First off, unless you score 100 on the exam, you can make an assumption that; 1) the student didn't understand "something", or 2) the instructors "failed" to teach something. I think both are bad assumptions. Not often any of us is perfect in everyway... except for perhaps Chris.

It is unfortunate that April_01 appears to not have a mentor to learn from (assumption on my part), but it certainly is no reason to slam her question. I would tend to agree that passing the ABOC exam does not an optician make, but it is better than nothing - right? Until everyone bands together and actually creates a channel that gets (forces?) opticians to be skilled, this debate will continue. There was once a movement (on this board) to do that (IOC), but due to lack of interest on the majority of people associated with this forum... it went nowhere. So here we are.

As for asking questions on this board, that could be found in any textbook, that's true enough. However, the advantage to posting here is seeing the various methods used (by different responders) to answer the question posed. And personally, I like seeing a variety of ways "to skin the cat". Sometimes people explain things differently - which can make the lightbulb come on.

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## wmcdonald

April,
I think it should be easily understandable to you why something so basic as decentration brought some question to the validity of the National Opticianry Competency Examination, commonly referred to as the ABO exam. Here is the problem with the question......it is the among the most basic of all things Opticians do every day. If you understand pupillary measurement and never work in a lab, you understand decentration. The ABO is suppossed to be the national certification exam to prove Opticians know they are doing. Obviously you missed that part in whatever study you did, and this verifies what many of us have said and continue to say, the ABO is not getting the job done. It does not measure Optician's appropriate level of competence. It is often tied to apprenticeship. I don't know who "trained" you as an apprentice, but they should never be allowed to do it again! I am sorry if Chris offended you whether or not he felt this was a joke, but he is correct! I as well do not mean to offend, and really I do not direct my comments to you, but to everyone else. The ABO exam needs to be strengthed so that potential Opticians that gain certification actually are tested on pertinent material. If Opticians are to advance professionally then the time has come for formal education requirements to assure competence, or at least improve the chance for it! I am tired of seeing young folks like April thrust into the optical world woefully unprepared and not realizing it. Hang in there April, and please understand I am not trying to belittle you only to make a case for better education and training. Opticianry is a wonderful profession and you will be able to continually learn throughtout your career. Good luck.

Warren G. McDonald, PhD

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## chip anderson

Until now Chip has no posts in this thread. I think the young lady deserved and got an answer. It is hard for some us (especially me) to be tolerant of those less experienced in this field but all questions deserve and answer. I do get irritated with those giving seminars as "experts" who seem to have their facts confused or have contradictory statements in their presentations, but novices need to be coddled, and we should do the coddling.


Chip

Young lady take heart in this.  I once had an old EENT man whom I think must have been the best muscle surgeon in the country (when he did a muscle surgery the eyes were straight the first time and stayed that way) anywayl, he came to me with an Rx for prism and said: "I am not a prism man, myself. Can't you do it wilth de-centration?"

Obviously he did not know that prism and de-centration are the same.

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## April_01

I would like to thank everyone for their opinions and to let you all know that I do not have hard feeling about anyone. I can see how frustrating it can be to have people like me who don't know a basic concept of opticianry and yet can have a title beside my name. That is why I have an intrest in this forum and a couple of mean remarks won't make me cry. 
As far as my training, for those of you who are interested, I started off my career as an optician at a Walmart Vision Center and trained through the WAVE program and my TOPS book. All of my studying was done by self study with no mentor. After I passed the ABO in May of '03, I applied for a tech position in a private practice in my hometown and got it. When I first applied I was really overwhelmed over all of this knowledge I didn't yet know, but through the coarse of this past year, my doctor and co-workers have really worked hard at mentoring me and helping me be more proficient at my work. I have recently took interest in the paraoptometric certification program by the AOA and it looks to be a little more efficient than the ABO. For right now, I still have some areas to cover and you can guarantee I will get more help and study my books more! I also want to thank all of you for your comments and suggestions it really helps to get second opinions and thanks to all of you, I don't think I will ever forget decentration!!!You are all like my second mentor and I look forward to talking to all of you again but hopefully with a more difficult question!
:idea:

P.S. Does anyone have any recommendations on what other books/coarses/programs to help raise my optical knowledge? :Nerd:

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## chip anderson

Go to the OAA.com for books and courses available.
Will have more than you can handle for a few years.

Chip

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## Chris Ryser

April,

When I was an apprentice, it was still the time when we were learning the ropes from the bottom up.

Lenses were glass only, we could not use the diamond lens cutter, there was no automatic bevel edger but a ceramic stone wheel. We ahd to replace hinges and solder frames. WSe where not allowed in to the store serving a customer for the forst three years. Had to go professional school for 2 full days a week for 3 years and then had an exam that lasted 2 full days in practical and theoretical optics. We had to master basic optics to pass the exams. The pay was lousy because the rule was that an apprentice makes as much damage in broken lenses and burned plastic frames.

You said in your last posting that you are using computers to do all the work for you. This actually means that in our modern world we can become anything by knowing how computers work and function. It does make sense somehow. Pilots are flying today and drop bombs onto certain buildings floors without seeing them. Cashiers in supermarkets scan the bar code, punch in the dollar figure you gave them and the computer tells them how much change to hand back.

In this case the examining bodies in any field will have to re-think their procedure how to certify professional people at the end of their learning period. We still should be able to exercise a profession in the case of a computer breakdowns.

When we think of our International Mega Companies now taking over the retail market, as well the laboratory market this could be the ultimate goal for them to have professionals out there to sell and service their goods without technical knowdledge. Then the market will have to rely purely on the direction of these new leader companies.  

April you had a rocky start on the Optiboard with some stirred up controversy and feelings from members. You did good by clearing the smoke but also awaken some serious concerns.

Welcome to the Optiboard and most of us who looked into this thread will now remember your name as a name and not a joke.

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## Spexvet

> I P.S. Does anyone have any recommendations on what other books/coarses/programs to help raise my optical knowledge?


Systems of OphThalmic Dispensing by Brooks and Boorish (sp?)

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## April_01

Thank you Chris. It means a lot coming from you. You seem very knowledgable about this field and it may sound corny but since this posting and your replies, I have been working harder and trying not rely on the computers for everything. I would love to go to school for this, but I live in IL and this is a non licensing state.I have researched on the internet about internet coarses/degrees but I haven't really found anything.That is why, unfortunetly for me and other apprentice's, we have to rely on the ABO/NCLE to learn from. I say unfortunetly because anyone can get hired as an optician in IL and I see it all the time, where they don't want to take time to do the work for a 50 cent raise especially if they are not forced to. This is sad because I consider this field for professionals who truly care about the patient,not just a way to make a quick buck.For me, this is my career I have chosen and I strongly feel I should take pride and learn as much as I can about what I do. Sorry for the speech. Thanks again to all of you for your help and support.

The books I am currently studing are:Complete study guide for the paraoptometric, The opthalmic assistant, and have just ordered Systems of Opthalmic Dispensing 2nd ed.(thanks Spexvet!)

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## Judy Canty

I would also suggest getting "Optical Formulas Tutorial" by Ellen Stoner.  It will be a huge asset in your studies.

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## Jacqui

Judy Canty:

Where can I get "Optical Formulas Tutorial" ??  This could be handy for my trainees. Any others that you would recomend ??

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## Judy Canty

Try www.nao.org.  I can also recommend "Essentials for Ophthalmic Lens Work" and "Understanding Lens Surfacing".

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## Chris Ryser

> *I say unfortunetly because anyone can get hired as an optician in IL and I see it all the time, where they don't want to take time to do the work for a 50 cent raise especially if they are not forced to.*





> *The ABO exam needs to be strengthed so that potential Opticians that gain certification actually are tested on pertinent material. If Opticians are to advance professionally then the time has come for formal education requirements to assure competence, or at least improve the chance for it!  * 
> 
> Warren G. McDonald, PhD


Maybe we should continue the discussion on basic technical knowdledge of the profession.

I never lost a thought on these unregulated states and that you can be a street cleaner or garbage collector one day and an optican the next. Sell prescription lenses as a novice to the patient or customer.

Therefore I must assume that these unlicensed professionals pick up their technical knowdlege from big company advertising and sales reps which are geared unidirectional in their own favour and use the un-educated professional to invest and sell their products.

It be very interesting to see some comments on the subject.

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## ikon44

how long does it take study wise to take the ABO exam, just curious as in the UK it takes 3 years to become a Dispensing Optician.I remember taking my finals using a slide rule to calculate a retinal image size of an object looking with a specific prescription, they allowed us 30 mins for that question because of all the calculations, these days i guess it would take 30 seconds with a lap top.

April i would reccomend professor Jalie,s book Ophthalmic Dispensing, I had the privelege of being one of his students.
He did,nt need a computer i am sure he has silicon chips instead of brain cells.

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## ziggy

April_01, What part of Ill are you in? I just moved from there and have a few friends that are fine opticians and they may be able to help with any mentoring. Gook luck!:)

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## drk

To Chris' point:

The best way to insure a profession's "professionalism" is to have very strict licensure requirements at the state level.  Strengthening those would increase the value of the professional.  Non-licensed states are missing the boat for their citizens, but, unfortunately I doubt there's any hard data that suggests that there has been loss of vision as a result.  Any that come up should be brought to the OAA.

What do you call an "optician" who is not licensed?  An optical assistant?  I think it's important to make a clearer distinction between the two.  "Licensed optician" and "optician" sound way too similar.

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## April_01

Ikon 44, You can take the ABO whenever you want you just have to have passed High School. I studied for a year and it was really easy,.......SO that is saying something! The more I get involved in this field, the more I realise the ABO really only teaches the very basics of optics. 

Ziggy, I live about 2 1/2 hours from Chicago in a very small town.

DRK, I strongly agree with you that every state should be liscensed. For the opticians that aren't, it makes us look unprofessional,unreliable,unkowledgble, sales persons. In my opinion on your question what to call us unliscensed folk: Optical Salesperson.

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## ziggy

I was in Decatur,,if its closeto where you are let me know.

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## Spexvet

I think April is looking for the formula to determine edge thickness. It's been a long time, but let me take a stab:


Diopters times radius squared divided by 2000 times index of refraction minus 1 all added to the center thickness (for minus lenses)

Maybe Darryl can help?

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