Printable View
Has anyone here taken the ABO exam recently? There are 2 things I can't figure out how to get the correct answer and my boss hasn't taken the exam in years and is on vacation, is anyone here able to help me with some example problems? I would be forever grateful!
It's been many moons since I took the exam, but what are the questions?
It’s asking for prism induced for -6.50 +1.50 x30 patient pd =64 fitted pd =68
options are:
2.45 BI
2.45 BO
1.225 BO
1.225 BI
I’ve tried figuring it out but I’m not sure how to get the correct answer? If you could help I’d appreciate it. Thank you
Find the power in the horizontal meridian (0-180). Then simply use Prentice's Rule to find the correct answer, P = hD.
You can use the power in any axis formula, but I think the ABO basic will always have questions at axis 30(120), 45(135), 60(150), 90, or 180. They want to you know the precent of cylinder present at each of these. So 25% of the cylinder power is present 30(120) degrees away from the axis, 50% at 45(135) degrees away, 75% 60 degrees, and all of the cylinder power is present 90 degrees away from the axis. You should still learn the cylinder power in any axis because it is simple and handy, but I don't think you get a calculator with trig functions for the test.
So the cylinder power present at 180, 30 degrees away the axis, is 25% of the full Cylinder power. .25*1.50= +.375. Add that to the sphere power -6.50 +.375 = -6.125. This is the power at 180. 4mm of decentration. .4cm*-6.125= -2.45. This is a minus lens with the OC displaced temporaly, so base in prism.
Cyl power in any meridian for future use is:
Dc'= Ds + Dc (sin˛θ)
Dc´= the power in the meridian in question (in this case it is 180°)
Ds = the sphere power of the Rx (-6.50)
Dc = the cylindrical power (+1.50)
θ = the difference between the axis of the Rx and the meridian in question (180 – 30° = 150°) or (30-0=30) or (30-180=-150) or (0-30=-30)
Dc' = -6.50+1.50(sin 150)˛
Note it doesn't matter if you use 0 or 180 and it doesn't matter which meridian you subtract from which, you will get the same answer. The sin of 30 is the same as the sin of 150, -30, and -150, and squaring the answer will remove the negative. So if you are looking for power at 180 you can just use the axis of the cyl and save some steps.
+1Quote:
Originally Posted by wmcdonald
With this type of question, be mindful if the solution is for "total prism induced" or "per eye". In the solution described in this discussion total decentration of 4mm was used. I'm inclined to think that since only one power was presented, mono decentration error of -2 mm should be used with 1.225 BI as the intended solution.
Again read word problems carefully to determine what the intended solution should be.
This is probably the right answer. I even thought about it, must have gotten distracted. I also think it's silly the ABO is more interested in tricking people with word questions, as opposed to actually challenging them with technical questions.Quote:
Originally Posted by PRECISIONLAB
Nothing at all tricky about this question. What is the power at 180? -6.12 D. 1.50 (.25) = .37. -6.50+.375 = 6.125 or on optical terms -6.12D. It is an Rx for ONE EYE, so you would use 2 mm as the "h" or distance, but remember Prentice's Rule is in CM, not MM. 6.12 (.2) = 1.224. Now, what direction is the base? If the PD in the finished Rx is 68, where the thickest part of that lens is located? I will let you figure that much out. Easy stuff if one understands basic optics, and a very solid question for any exam of this type. It requires some complex thought to do what an professional Optician does every day, and the question requires that thought along with the determination of the induced prism.
Thanks for explaining that to me the exact same way I already wrote how to solve the question. smh.Quote:
Originally Posted by wmcdonald
My point is that I have never in my career used the rule of thumb ABO wants the applicant to know. I have many, many times used the power at any meridian formula.
The question and multiple choice answers are clearly written to trip people up and not test their knowledge. Maybe make the test not multiple choice for starters.
If they are going to go down the road of trying to trip people up who might read the question wrong, they should be very specific in their question. No where does this question say the Rx is only for one eye, at least the way it was presented here. Without that one could just as correctly assume the Rx is the same for both eyes. Since they also didn't specify total prism or prism for a specific eye, one could also correctly assume either. Before you say that it would have said OU if it was for both eyes, it doesn't say OD or OS either so... It also doesn't specify monocular PD's or monocular decentration, something any worthwhile optician would have in front of them if they actually needed to figure this out for a job. One could assume they are symmetrical, or one could assume they are not. Maybe the PDs are 34/30 or they are fit at 36-32, who knows unless they tell us.
This is a very basic question, I agree. The ABO basic is a joke of a test. However, the questions are very much written to trip people more than they are to demonstrate the basic knowledge requirements for an optician. Especially when they don't specify important information.
Yup, as written, there is insufficient data. Most folks have two eyes, with two corrective lenses. We're forced to assume both eyes have the same power in the 180 meridian. Punt.Quote:
Originally Posted by PRECISIONLAB
Adrianna, did you copy the question verbatim?
Hint: Wide OCs with minus power induce base in prism, and base out when narrow. The opposite for plus. (Visualize the lenses as two prisms connected base to base, or apex to apex, and the position of the pupil in relation to the base and apex).
In this question, the OCs are wide so you can rule out two of the multiple choice questions right out of the gate.
If the fellow eye has the same power in the 180 meridian, the answer is 2.45 prism diopters base in.
These test questions are almost always written so that the answers can be derived by simple mental math, as long as you understand the principles.
Hope this helps,
Robert Martellaro
My response was a simple version of your well written description and intended for the OP, not you. I know you understand this very well, but they did not and I just made it simple. Not intended to be offensive.Quote:
Originally Posted by Kwill212
Folks, objective tests like this are the best way to make examinations most objective. If this question tripped up anyone, they need to go back and learn a bit more. Because it is objective (there is one best answer if one understands 3rd grade math), it DOES require thought. But there is far more to test writing than you may assume. The ABO/NCLE finds the best minds in this industry to write questions, but beyond that they are psychometrically evaluated to measure their objective value, meaning that the majority of the population of test-takers would find it understandable. These tests are re-evaluated regularly at a cost of hundreds of thousands of dollars. If anyone feel as though they would like to help write these exams, I am sure they are always looking for assistance, and I will be most happy to recommend these experts to the cause.
Today's ABO is a far stretch from the old exam, written like some independent state boards. It is well-developed and covers a lot of material. And to assure it is written effectively it is reviewed after exams by not only the board themselves, but outside testing agencies.
Nothing wrong with this question, and my comments are intended to help the OP.
To the OP........you will find many different opinions here, and you must sift through them to understand the real issues. The problem we have some really solid folks here who are passionate about the industry, bu all have different backgrounds, and no common training. It is a micro chasm of the entire industry, where now 21-22 state are licensed, and the rest require nothing.....no education or training......nothing. In those states, the requirements vary across each of them. A confusing mess, but understand the site here can be helpful. I hope you have gained from this conversation
Best regards to all,
Warren
Hi and how are you. I took the exam recently and passed, I will do my best to help. Please write back and i will see what I can do to help you
Prentices rule is being used incorrectly. It will only provide a correct answer with a spherical power or where the axis is 90 or 180. As an extreme case to show why it does not work. Rx +2.00 -400 135 will calculate to no power in the 180 meridian so pd does not matter. In actuality you will create Bu or Bd depending on which way you decenter. You will always create oblique prism when the axis is other than 180 or 90. This should be taught correctly not using a rule of thumb. A rule of thumb does not always work that is why it is a rule off thumb not a law of physics. Try the induced prism calculator in Opticampus to obtain the correct results.
To build on Lensman11, one needs to calculate the true power at the 180 and the 90 to properly apply Prentices' Rule.Quote:
Originally Posted by Lensman11
The ABO uses extensive psychometric analysis of questions to assure they are objective. No trick questions. But you are correct in one regard, it needs to specify monocular or binocular. I suspect it does.Quote:
Originally Posted by Kwill212
We have a staff member that is going to take it soon. How fast did you get your results back?Quote:
Originally Posted by davidefolder
Folks,
Several here are mentioning things finding the "true power", and vertical position, etc. But on a test like this, you must respond to the question as written. In this case it is simple. No index of refraction of a given material is provided, so true power is not possible. The True Power formula requires this small detail. We are not provided fitting data, so no way to determine prismatic values in that regard. This is a simple, straight forward question most should be able to answer. The only criteria provided requires that the individual taking the exam us Prentice's Rule (and it is being used in the correct way) to find basic power once the basic power in the meridian is determined. In this case, all that is required is flat transposition. This formula is an approximation, but it is a very close one and applicable to the field since Charles Prentice developed in around 1905. This, and every other question is measured after each exam, and the ABO/NCLE boards can stand up to as much scrutiny as anyone wishes to give them, and to legal challenges. They have the data to back up their work, and I wish people who have not seen this exam in many years would understand it is different today than in the past.
To the OP.......posting a question here can be helpful. But it can also be confusing. I hope you are able to sift through this morass of opinions, and well meaning folks. Those who are more advanced here are correct in what they are saying, but you must understand more than the basic level to be able to delve into the more advanced topics. Find a local mentor. One who can help you. Unfortunately you are in Louisiana, where the requirement to be an Optician is a pulse, so I cannot offer anyone to assist at this point. Most of my connections there, like me, are old and done. But in today's world, you can find help via Mr. Gore's wonderful Internet. Possibly one of the folks who are more advanced here can offer assistance. I will be happy to help any time as well.
Folks,
Several here are mentioning things finding the "true power", and vertical position, etc. But on a test like this, you must respond to the question as written. In this case it is simple. No index of refraction of a given material is provided, so true power is not possible. The True Power formula requires this small detail. We are not provided fitting data, so no way to determine prismatic values in that regard. This is a simple, straight forward question most should be able to answer. The only criteria provided requires that the individual taking the exam us Prentice's Rule (and it is being used in the correct way) to find basic power once the basic power in the meridian is determined. In this case, all that is required is flat transposition. This formula is an approximation, but it is a very close one and applicable to the field since Charles Prentice developed in around 1905. This, and every other question is measured after each exam, and the ABO/NCLE boards can stand up to as much scrutiny as anyone wishes to give them, and to legal challenges. They have the data to back up their work, and I wish people who have not seen this exam in many years would understand it is different today than in the past.
To the OP.......posting a question here can be helpful. But it can also be confusing. I hope you are able to sift through this morass of opinions, and well meaning folks. Those who are more advanced here are correct in what they are saying, but you must understand more than the basic level to be able to delve into the more advanced topics. Find a local mentor. One who can help you. Unfortunately you are in Louisiana, where the requirement to be an Optician is a pulse, so I cannot offer anyone to assist at this point. Most of my connections there, like me, are old and done. But in today's world, you can find help via Mr. Gore's wonderful Internet. Possibly one of the folks who are more advanced here can offer assistance. I will be happy to help any time as well. Whoever it is, find someone with an education and background to truly provide the guidance you need to maximize your potential. This field has languished too long in the fields poorly developed apprenticeships taught by high school educated folks who never really learned themselves.
When Prentice came up with his infamous rule Toric lens were rare expensive and hardly used. I don’t think he even considered the effect of a lens with two powers.
I don't think you are correctly applying Prentice's Rule if you think it doesn't work for your example.Quote:
Originally Posted by Lensman11
Vertical prism is induced when horizontally decentering a cylinder. You can calculate it using Prentice's Rule and some Trig. The sphere power is irrelevant for this situation. Find the cylinder power at 90°. sin˛(135-90)*-4.00D=-2.00D. Then calculate the vertical decentration of the cylinder solving a right triangle. Assume you decenter horizontally 5mm. Tan(135)=X/5) which means X=-5 where X = vertical decentration. Then simply use Prentice's Rule to determine the induced prism. .5cm*2.00D=1D vertical prism. Obviously you would need to correctly input the signs to get the correct direction up or down, or draw it out. Your example doesn't really require trig if you know the basics, but this same method works for cylinder at any axis and power.
For example.
-5.00 -3.25 x 062 decentered 6mm horizontally. Cylinder power at 90° is sin˛(62-90)*-3.25D=-0.72D. Vertical decentration is Tan(62)=X/6mm. X=11.28mm. Prentice's Rule is 1.128cm*.72D=.81D vertical prism.
I'm can only assume you have never read any of Charles Prentice's work if you think that is the case. Ophthalmic Lenses, the e-book is free on google books, you should give it a read.Quote:
Originally Posted by Lensman11