Optician Training: Working Through A Challenging Prism Problem

Walk through a “brain-teaser” prism question. We take a real world prescription and pair of glasses and create an error in the as worn position. Solving for the final correct answer is a multi-step process that requires some time, patience and visualization skills. If you can figure out a question like this you can handle anything the ABO might throw at you.
Learn More: opticianworks.com/
This question is similar to one found in our American Board of Opticianry ABO test question bank. We take a real world prescription and pair of glasses and create an error in the as worn position. Opticians often use Prentice’s Formula to solve for prism problems. Solving for the final correct answer is a multi-step process that requires some time, patience and visualization skills. With optician training you can determine prism amount, prism direction and resultant prism. Working this problem through will help you study to prepare for the ABO exam.
Learn More: opticianworks.com/
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This video lesson is sponsored by Laramy-K Optical
Laramy-K Optical is a digital uncut and coating lab unlike any other. The only exclusively uncut lab in the country; we provide our customers with independent, high-end alternatives to corporate brands. Through craftsmanship, technology, and independent, innovative vendors like Younger, IOT, A&R, and Quantum Innovations we offer our customers the Integrity portfolio of freeform lenses and coatings. Made in the USA, the Integrity brand is not a generic house-brand, but is the absolute best available, designed to give the wearer that “wow!” experience.
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[@chadjohnson3736]

Hey John I saw the chart on the video but I didn't know if there was a mathematical equation to figure out the percentage of cylinder power felt. Because I know I won't be able to use that chart during the ABO test

[@LaramyKOptical]

Chad, Actually I'm pretty darn sure that you are EXPECTED to use the 30/45/60 % rule on the ABO. At least everything I see for ABO prep covers it. You might want to hit Facebook and ask people that JUST TOOK it. The Optical Guild, Optical Mentors or even Opticians on Facebook. Ignore the comments from the folks that took it 10 years ago. John

[@stegbar]

How can you determine whether a prism is a base up or down, based in or out, from prism calculation?

[@LaramyKOptical]

Plenty of other videos and the OpticianWorks website. kzbin.info/door/dfKXBLjBDbX2X2g0XuAbmwvideos

[@MK-ns7qk]

Hi John, thanks for the great video but i have a question in this example if we had a bifocal lens of say +2.00DS how do we use the prentice rule. Say the last example of jamal but he had a +2.50 add and been decentered 1cm up? do we just add +2.00 to the meridian power at 90 and then used the prentice rule?

[@MK-ns7qk]

typo - do we add +2.50 not +2.00

[@LaramyKOptical]

Whoa - way, way overthinking things here... add powers don't play into the concept at all. In a lined style the segment isn't placed in a position where it would matter, in a progressive prism doesn't work the same way. The Prentice's stuff is just a concept, it isn't used in determining any prism that might be required. Keep watching the other videos and most important watch the three (all 3) on verification ! The only time a segment and "prism" would come up would be image jump and there is a video on that. A million years ago some people used to use differing segments to overcome some prism issues but those styles aren't even available anymore.

[@MK-ns7qk]

Thank you very much for clearing this up for me…. I was definitely over thinking it.

[@juanisaza4756]

Jhon, thanks for this good explanation. my question is The ABO give us access to an computer calculator to figure (sin a). or how the test taker should figure that out?

[@LaramyKOptical]

You will need to check with the ABO but last I heard you either get a basic calculator or a basic on screen calculator to work with. You will not need to work the power in oblique meridian formula. Just stuff that requires basic math like the percent rule.

[@aaamart4]

calculators provided have sin and square functions.

[@LaramyKOptical]

@@aaamart4 But do you need or use those functions on the basic written ABO??? I think not? Please let us know. John

[@aburashed6]

Hi jhon can you explain the difference between total power and range power

[@LaramyKOptical]

Not 100% sure what you are asking - but - a sphereo-cylinder lens that corrects for astigmatism has different power in each of the 180 (360) degrees of position. If you pull out one meridian that would be total power. The power at each of the two principle meridians would be the range? Again, not sure. John

[@chadjohnson3736]

I understand that you're - 180 degrees from the cyl power that you have 100 degrees and you're left with 80 degrees but then how do you calculate that it's 97% of ur cyl

[@LaramyKOptical]

Chad, I show a chart at 4:15 and again at 4:43 that shows you. It is also covered in earlier videos and on the website too. The actual step-by-step on that part of the process is covered in the videos leading up to this one. It is only a short-cut. Same as the 30/45/60 rule. John

[@aaamart4]

DT=(sin a)2 x Dc + Ds (( Dc =cylinder, Ds =spherical)) =(sin*80)2 x Dc + Ds =(0.97) x (-1.50) + (-7.00)

[@nexx1]

A real world example of this is when I see men in turban, wearing their glasses, with one arm inside the turban and one arm on the outside of a turban and it pushes their glasses towards one side and then they complain they can’t see.

[@LaramyKOptical]

LOL That would have been a great real world case study example!

[@emma0o056]

Thank you too much , but how you know the glasses will shift 6.5mm , I mean how you can know the exact amount?

[@LaramyKOptical]

These examples are all practice and/or visualization exercises. 6.5 was just randomly assigned as hcm to make things interesting. If you are a consumer - don't worry about it. If you are an optician join OpticianWorks.com.

[@emma0o056]

I got it , thank you

[@nexx1]

1.50sin(80)2=1.45+7=8.45 1.50sin(65)2=1.23+6.50=7.73

[@likei8301]

Why are you multiplying by 2?