30/33 correct! *Pats myself on the back* ... Bring on the advanced exam!
30/33 correct! *Pats myself on the back* ... Bring on the advanced exam!
Congratulations Jonathan,
I will send you my emial if you want to talk about the advanced test. I took it in 2013. As you would expect there are things you need to know for the advanced that are not on the standard exam.
Deb
Funny...many of the test questions posted look very similar to the questions that were on my basic ABO certification test back in'89
Oh and by the way ..a belated congrats to you Jonathan! You know your stuff!
Last edited by tx11; 10-24-2014 at 09:47 AM.
Looking a this makes me realize how stupid I really am. I feel like I'm a fairly good Optician, but wish I was more intelligent in the depth of optics as you guys. You'd think, being in this business 26 years I'd know more... guess not. I've looked on ABO-NCLE.org, I still don't see any study materials for Advance ABO Testing.
That is the overarching problem with Opticians in this country. They often get offended, and I hope you do not, but this group of people really has no clue what they do not know. Like you, they all feel they are pretty good at what they do, because they have done it for a long time. We must get better somehow if we are to remain relevant at all in the field.
wmcdonald...........there comes a time when the rewards are not always worth all the knowledge that one could ever have about optics. Not everyone has a desire to walk around with a head stuffed full of optical knowledge that they may use bits a pieces of every other couple years or so. My suggestion is if you want to dispense know all their can be known to be the best damn dispenser possible. If you want to work finish then know all there is to know about finishing and the equipment so that no one will be better then you. And the same goes for surfacing. If you want to get into lens design and material frame design and materials then be the top expert in that area.
But it sounds like your suggesting to be super knowledgeable about all areas. Realistically not practical. Unless of course you want to own your own business. And most of us know how many hats that will entail. The list could go on and on.
The NAO has a textbook on the Advanced Exam. http://www.nao.org/?page_id=2625#toggle-id-12 I also used Optical Formulas Tutorial by Stoner, Perkins and Ferguson. Do not get too bogged down, this book goes way deeper than the exam will, concentrate on the formulas that are referenced in the NAO textbook. I can honestly say that studying for the exam expanded my knowledge of optics and helped me understand the concepts behind lens design better. You will enjoy the topic it is broad and fascinating. It had been way to many years since I had dealt with trigonometry and I had to learn how to use an algebraic calculator, but I enjoyed it all the same. It is great that you are interested in growing your knowledge of optics to enhance your already impressive dispensing skills. You are far from stupid, don't be discouraged, I gaurantee you that many of us who are now certified Master Opticians had to study hard for this exam. For me it had been too long since I had taken trigonometry and I had to learn to use an algebraic calculator. Am I giving my age away? If you don't let yourself get intimidated most of the answers can be worked out without even using the calculator. This requires that you understand it rather than just memorizing formulas. I hope you go for it. By the way the formulas are provided as part of the exam material. So, do not waste energy stressing over memorizing them...instead put your energy into terminology and knowing what the formulas solve. Of course you have to understand the order of operatons for inputting the formula in the algeabraic claculator. This is in the Optical Formulas Tutorial. Much of the material is not all that advanced but because it is not something we deal with on a daily basis you would have to memorize the information.
I understand your perspective, and appreciate it. But the lack of knowledge in most areas today is quite disturbing. Until we improve our basic level of knowledge, we will go nowhere as a field. We are not called finisher, and dispensers (I hate the term......I get shaving cream from a dispenser), etc. We are called Opticians, and we need a requisite sphere of knowledge that all who use that title bring to the table.
Not sure if I agree with C being the right answer? Just trying to get some clarification as I am taking the advanced test next month. My calculation would be more of a near PD of 57.5? Correct me if I'm wrong but wouldn't you add the distance Rx along with the add power as that is how the Pt would be viewing it? Mathematically that seems to make more sense to me, but I guess I can cut it tomorrow and find out. Also I would be interested in any advice I can get on the Advanced Test. Thank you for any and all help.15. Given the following FT-35 bifocal prescription:
+2.00 DS with a +2.50 D add, O.U. (both eyes)
PD’s = 66/62 mm
How could you induce a 1D base in prismatic effect, per eye, at near only?
a. Use a 56 mm distance PD
b. Use a 60 mm near PD
c. Use a 54 mm near PD
d. Can’t be done
"Hi Mike,
Brooks makes no mention of neutralizing the prismatic effect at distance because it is not necessary. Essentially, you will still be placing the distance optical centers in front of the pupils (assuming that the distance Rx doesn't call for prescribed prism). You are simply decentering the bifocal segments from their intended locations, which changes near prism -- not distance prism. Consequently, the power of the distance Rx will not play any role either for the calculations.
Basically, the bifocal segment acts like a little plus lens. If you have a PD of 60/57, you would normally place the distance OCs at 60 mm and the segment centers at 57 mm. To determine how much to decenter the segments from that point (57 mm), you need to use Prentice's rule with the segment. The add power of the segment is used.
Prism = Dec (cm) * Power
3.00 PD = Dec (cm) / +2.50 D
Dec (cm) = 3.00 PD / +2.50 D
Dec (cm) = 1.2 cm = 12 mm
Since you need base in prism, each bifocal segment would have to be decentered in an extra 12 mm. This means that the segment near PD would have to be 57 mm - (2 * 12 mm) = 33 mm to induce a total of 6.00 PD base in. The distance PD should still be set to 60 mm.
Unfortunately, obtaining this much prism at near by decentration requires a great deal of inset. Oversized (e.g., FT-45) or Franklin-style segs will be necessary to get a sufficient field of view through the segments, unless you use prism segs or Press-On optics or something. You can cut down on the amount of decentration necessary by either increasing the add power or by cutting back on the prism at near. Good luck.
Best regards,
Darryl"
per an old post from Darryl
http://www.optiboard.com/forums/show...g-decentration
If we ignore the prismatic effect of the eyes converging behind the distance Rx, a near PD of 62mm - 8mm = 54mm (.8cm x 2.50 D = 2∆ BI total) is the correct answer.
If we include the effect of the distance Rx which is 2.00 D x .4cm = .8∆ BO total, that can be cancelled by decentering the segs an additional 3.2mm (.32cm x 2.50 D = .8∆ BI total). A near PD 50.8 achieves a resultant prismatic effect of 2∆ BI total during the near gaze.
I'm not going to consider the fact that the eye will rotate towards the prism apex .3mm per prism diopter upsetting the distance calculation in a way that's somewhat like going back in time and killing your grandparents.
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
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Ok, so I ran a pair of glasses running the scenario from the test and get 4 base in OU, 2 diopters of prism per eye? The only way the scenario would work in real life application from what I can see is if there was no Rx for distance?!! Also while playing with lenses I'm looking at stock lenses with no Rx verses lenses with + Rx' and the ones with + Rx' require less movement to get the same amount of prism induced as the stock lenses with no Rx and the same add. I am by no means at the level of optical knowledge most of you that have responded have, I'm sure but I would highly appreciate further looking into this and getting to the bottom of it, because the theory behind what I've read here and the actual putting to the test is not matching up.
And I guess to add to this theory, wouldn't the way we calculate for the amount of prism needed for Bicentric Grinding come into play to a degree, theoretically of course.
Last edited by King.Matthew; 07-24-2015 at 11:26 AM.
Given the following FT-35 bifocal prescription:
+2.00 DS with a +2.50 D add, O.U. (both eyes)
PD’s = 66/62 mm
How could you induce a 1D base in prismatic effect, per eye, at near only?
1. Find the inset
Seg Inset is 2 mm
2. Find the additional inset needed
* 0.4 cm or 4 mm
* New Seg Inset = 2 + 4 = 6 mm(double this for total)
* 66 - 12 = 54 NPD
66/54
I'm in King's camp. There are two OC's on a segmented bifocal. If I'm moving the near only OC to create prism in the seg only, I have to use the total power at the near OC to compute the total decentration to achieve "X" prism.
I also took a look at a lens I have here that happens to be a FT35 +3. dist/2.00 add. The power at the near OC is a +5.00 I move it 4mm in my lensometer and I get 2D prism (in any direction.) Thus, if I want to induce 1D prism with my test lens I only need to move the OC 2mm.
If me and King are wrong, I'll need a better explanation than what I understand (and demonstrated to myself).
Measured at 62 mm? Consider the seg as it's own lens. You are only moving the near seg. The distance OC stays in the same place, at 66mm. Any small amount of prism in the distance portion of the lens at 62mm will stay the same as the seg is slid in. How far do you have to move a +2.50 to induce 1 diopter of prism? 4 mm right? Now do the other eye. Same answer, for a total of 8mm. Therefore, 62mm - 8mm = 54mm. Measure the result at 62mm, where the patient's near gaze falls.
Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA
“As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein
So, for arguments sake, If I have a -2.00 dist/+2.00 add, I can inset the seg 5mm and induce 1D of prism (in a plano powered part of the lens?)
How much prism is at the Distance OC of that lens? None. Assume a seg inset of 1.5mm. How much prism is at the near OC? .3 diopters base in due to the -2 carrier. We aren't really considering this, though, because it will be there regardless of where the seg is actually moved. If you move the seg in 5 mm, now how much prism is there, 1.5mm in from the distance OC as the eye drops into the seg? Actually 1.3, but we disregard that .3 for the thought experiment. If you wanted to be nitpicky, you'd actually slide the seg 3.5mm, for a total inset of 5mm vs 1.5mm to get exactly 1 diopter of base in prism at near only.
If you had a +2 seg and a +2 carrier, you'd have .3 base out in the carrier as the eye converged and dropped into the OC of the seg. Therefore, you'd technically move the seg 6.5mm in instead of 5mm to get that 1 diopter of prism base in at near only. But again, we normally disregard the .3 for the thought experiment.
You have to think about the seg as its own lens to begin to understand it.
Last edited by Wes; 07-24-2015 at 05:01 PM.
Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA
“As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein
Just for the record my last name is King, LOL. Wes, I completely understand where your coming from, my problem is the theory and the actual results in lab are not matching. I will run the test with a -2.00 in the distance with a +2.00 add tomorrow to find out what will happen. But like I stated earlier I plugged in the number's 66/54 +2.00 with a +2.50 add and got four base in prism total measured at 62mm. So this tells me that the calculations are wrong?
And again why would it be different than the calculation for vertical calculations where one finds out how much prism is in the distance and then adds the add power to the distance power to figure out how much prism is in the near part?
The calculations aren't wrong. Something went wrong in your process. Spot up the distance PD and see if it's actually 66.
Wesley S. Scott, MBA, MIS, ABOM, NCLE-AC, LDO - SC & GA
“As our circle of knowledge expands, so does the circumference of darkness surrounding it.” -Albert Einstein
I will recheck it tomorrow in the lab, have you done this in actual glasses or just in math? A Dr. I used to work for would request base in prism in the near about 2 times a week on our older patients and I would always calculate it out using the distance Rx in connection with the Add power? I guess I could have been doing it wrong but the results using my method always portrayed the end result I wanted. I guess I would say don't take my word for it, try it in your lab tomorrow and see what you get? I would be interested to know what your lab equipment does with the Rx of +2.00 with an Add of +2.50 and the PD 66/54?
It's easier to treat the bifocal part as a separate lens.
Think about it this way, if you had a SV +2.00 DS OU with a PD of say 62mm
if you wanted to make a +2.50 DS OU clip on that induced 1D of BI prism per eye,
what would the PD of the clip on need to be?
assuming of course that the front curve of the +2.00 lens, and the rear curve of the +2.50 clip matched exactly, and there is exactly zero space between the two.
edit:
I believe the problem/miscalculation is in the fact that we are trying to achieve near BI prism relative to the distance Rx, not relative to no Rx.
Of course if you take a +2.00 DS ou +2.50 add and place the bifocal segment OC in front of the pupil and then decenter(by finish blocking), you will use the full reading power(+4.50) to calculate induced prism.
But that's not what the problem is asking.
The problem is basically asking how much surface decentering of the segment is required to achieve BI prism at the near Rx only.
When you surface decenter/block a bifocal/trifocal, you are moving the segment away from the OC.
It's part of the reason why you don't surface block a bifocal with the segment at the generator blocks geometric center.
It's also the reason when ordering a Bifocal from a lab, you are supposed to supply OC height/seg drop, and both distance and near PD, to prevent unwanted induced prism.
Last edited by ml43; 07-25-2015 at 04:14 AM.
So, does this rule only work with flat tops? Wonder if I was doing a Franklin bifocal with a -2.00 dist/+2.00 add? I would be using a -2.00 for dist and a Plano for near. How am I going to decenter the plano's OC enough to get 1d of prism?
I'm really sorry guys. I hear what you are saying to think of the seg as it's own little lens, but in my minds lensometer, it's not seeing it!
Last edited by optical24/7; 07-25-2015 at 04:56 AM.
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