If it helps for prism, the way I understand it is; PT PD is Right eye or (OD) 31mm and it was received at 33mm, that 31-33= 2mm BO (base out) because the received PD is larger than the PT PD. In the OD the prescription is a minus lens (-) when the RX is minus we change the base to the opposite direction, in this case meaning BI. If the RX was in a plus lens (+), then we keep the same base direction meaning that our base would stay as BO (base out). Hope this helps! Great videos, I am refreshing my memory for my BOARDS!
Thank you!!! Prism has always been super difficult for me to understand and I really struggled with base directions! This video really helped me to understand this! Thank you so much for taking the time to do these videos! They are absolutely wonderful and you actually make them interesting to watch. Keep up the great work and again I can't thank you enough!👍👍👍👍
Hi John love your work and your videos and am currently studying to become a licensed optician dispenser however, m having trouble with the first example. At 3:30 how did you get 0.25? For the -2.25x0.25= -0.56 equation
You need to start with the first video and work your way up to this part II one. It has to do with where on the lens the power is. We cover the optical cross, 30-45-60 and then PIOMF first.
At 21:11 OD follows the -1.25 x 0.25 = 3.13 formula, but on the OS would it not be the same? OS -1.50 x 0.50? Im having a hard time figuring how you got 1.63.
Hi John, at 24:00 you say that the correct answer is 1.4 BI R, 1.4BI L. I'm getting confused because 1.4 diopters is how much total prism is induced (0.9 in R and 0.5 in L). It almost seems like you're saying there's 1.4 diopters in both eyes. Could you please clarify why you would write it as you have? Wouldn't you just say 1.4 diopters base in R, since the R eye has the greater power??
Hey John, your videos are extremely helpful! Just a quick question. At 12:09 you mention the final answer of .5 prism diopters in the left eye, but left out the direction. Would having the direction make the answer wrong? Thanks so much.
Rom, Great catch! You are 100% correct the complete answer would be 0.5 diopters BASE OUT in the Left. Sorry that IN is misleading and the direction is missing there. Next time! John
I’ve been watching all the videos up to here, and I may have missed it, but are powers weakest at 180 and strongest at 90? For 180, you take a reduction based on the cylinder to the power on the prescription, and at 90, you add based on the cylinder to the power of the prescription?
@@LaramyKOptical thank you funny enough after I posted my message I went back and re-watched the first couple of videos and definitely understood it better the second time around. Thanks!
@@KingsKnightNumbaTres I don't find exactly where that occurs but, yes, that is the most likely answer. I'm not very good with math and a very sloppy "rounder upper-downer." John
Hi John thank you for your helpful videos. About the Danika’s and Jamal’s on the left eye at @180 I don’t understand why is 1.63. The rule is not -1.50x0.75 that is 1.13? Thank you
Renata - You need to work the rule all the way through. As I mention in the video you should have watched the 30/45/60 rule video before starting this one. -1.50 X 0.75 = -1.13 which is then added to the sphere power of +2.75 for a result of +1.63 total power in the meridian of 180. It is the combination of amount of cylinder in play combined with the sphere! John
Hi Sir, thanks a lot for your lessons that are extremely helpful for newbies like me. I have 1 question at 10:23 of the video. I couldn't get it why 0.2 x -7.56 = 1.51, shouldn't it be a minus result as -1.51? I know I miss something to understand it. Could you please help?
Prism doesn't have a sign only an amount and a direction. You need two prisms together to create a focal point or a positive or negative vergence of light. Prism is only about the perceived shift in position. John
24:19 - I think the way this should be written is 0.9 prism BI OD and 0.5 BI prism OS. The reason why is the way you have it written, 1.4 BI OD and OS, that gives you a total of 2.8 prism diopters. The answer needs to show how much prism is induced in each eye individually. Each eye induces different values (0.9 and 0.5) not 1.4 in each eye.
@@LaramyKOptical Yes we did do compounding prism. 1.4 BI would be the right answer if it said 1.4 total BI prism OD or OS only.. if you say 1.4 for both, that gives a compound total of 2.8 which isn't the total. Am I thinking of this wrong? 0.9 total BI OD compounded or added to 0.5 would give you 1.4. But TOTAL, not 1.4 for each eye individually.
The rule says, Compounding: Write the result as total amount in both eyes with direction for each. 0.9+0.5=1.4 for a total, total in each eye 1.4 expressed for both the R and the L. The answer as written @ 25:09 in the video 1.4 BI R and 1.4 BI L is correct. I'm not sure why you want compound it again? It is already compounded when you add 0.9 and 0.5. ?????
As an optometrist, if someone wrote a glasses prescription with 1.4 BI OD and 1.4 BI OS, that would be a total value of 2.8 prism of BI. The total amount of induced prism in this problem is 1.4 BI. So I think our confusion is are you saying 1.4 BI OD 1.4 BI OS is the same thing as saying “the total amount of induced prism in this pair of glasses is 1.4 BI”?
@@eyeeric9686 I'm really not sure what to say. That video has been up for over two years and has had 11,000 views. That example is also used in the ABO prep questions which have been taken over 7000 times and no one else has had a problem with it. The answer as written to the rules is as shown. I don't think the idea behind it is to say your result is any way equal to or the same as the amount of prism you desire. In fact the exact opposite. So it wouldn't be written that way. ????? The answer to how much ERROR was created is _____________. Not the answer is equal to this prism notation on a written prescription would be _______________. ????
@LaramyKOptical I gotcha'! I was able to follow your way just fine but that's how we were taught in school. Looking at it, do you think there's any negative going with that one rather than yours? D= power X d= decentration and answer divided by 10? Thank you
Hi John, In 23:22 wouldn't the prism be BO instead of in? In your part 3 video you use a similar diagram and say it is supposed to be BO as well. By the way your videos are helping me so much for studying for the ABO test.
Morgan, Mmmmmm... if you freeze the video at 23:22 it can't be much clearer. The red dots are the lens OCs and the black dots are the wearer's pupils. Both those OCs are IN towards the nose. The base of the prism is IN for both eyes. You are only looking at the single triangle that the pupil falls within. Don't look at the "lens" look at the prism. John
It is soooooo easy to get confused... whenever I get a question like yours it takes me a few minutes to work through it and get it all again myself. The only thing worse is compensated powers! John
Osaf, When it is done deliberately it is to correct a problem in the way the brain and the eye see things. Maybe the right eye sees an object where it actually is. But, the left eye sees it 5cm over from there. You can use the image shift to bring the two together. I have more about that in the other videos and much more on the website. John
You can also use another formula subtract axis from 180. 180-150=30. Cyl -2.25sin(30)squared. 2.25sin(30)2=0.5625 Then add sphere +7.00= 7.56 Then multiply by by the Pd error 7.56*0.2=1.5 prism
Now I'm confused. It is shown/drawn on the whiteboard. I'm guessing you are missing both the concepts of lenses as prisms and orientation 180 or 90? Or you are missing the entire process of determining error. This isn't one of those things you can sort of pick up in the middle. I'd head here: www.OpticianWorks.com. John
@@LaramyKOptical i went back and reviewed the previous videos for a 2nd time and I think I figured out what I was missing. Thanks for building such a helpful channel for opticians!!
@@LaramyKOptical so im going back through the previous videos and feeling confusion as well. to be specific, what was the determining factor for drawing the different shape on Left eye? I realize that the lens moved down because the OC moved up and now has a positive number. why is one lens the hourglass shape and the other is the diamond shape... Im missing that deciding factor somewhere...
I think I figured it out...is it that the hourglass shape is associated with the minus lens power. and the diamond shape is associated with the plus lens power? It is the same for moving along the 0-180 horizontal space too...
Had a tricky question in my ABO exa. Pt have an RX at +1.00 -0.50 x 180 OU, if looking at 5mm above the OC, what prismatic effect will the pt experience? Base in? Out? Up? Or down?
HELLO!!I BECAME FAN OF YOU AND YOUR VIDEOS,YOU HELPED ME A LOT!!!WELL I HAVE THE QUESTION AT THE PREVIOUS EXAMPLE...WITH THE CANCELLING EFFECT,YOU SAID AT THE END 0.5ΔINL,BUT THE BASE WAS OUT....WHAT I MISS????THANK YOU AGAIN!!
The videos you present are outstanding sadly many opticians have to learn this way as formal training is not required to claim the title of optician. I believe that Prentice rule (that is why it is a rule not a law)does not produce the correct amount of prism in cases when the axis is other than 90 or 180. An example would be +1.00 -2.00 x 45. The power would be 0 at 180 allowing any pd to be acceptable. That is not the case you induce up or down prism depending which way the decentration is off. Put a lens in vertometer and move to observe the result. To actually understand the amount of prism induced you have to calculate the induced prism in each primary meridian and calculate the resultant prism. In this example the resultant prism would be at 90 giving you up or down prism depending on the direction of the movement. Your instruction is a rule of thumb that will most often produce an acceptable answer but one must understand when it will not work at all. Few opticians can calculate crossed prisms so it would probably be easier to get the result mechanically in the vertometer.
The solution I offered in my previous post here about a week ago (regarding your 2nd example in this video) was incorrect. I have deleted the post. I have since verified that your answer is correct. I apologize. I have since corrected my own methodology (a bit different from yours and retaining, and making directional use of, the +/- signs throughout the solution process). Sorry for any waste of your time and consideration. I do appreciate and enjoy your videos despite being a non optician layman.
![Felix "Unfair" | [Stray Kids : SKZ-PLAYER]](http://i.ytimg.com/vi/Oswujxm2Ag0/mqdefault.jpg)
If it helps for prism, the way I understand it is; PT PD is Right eye or (OD) 31mm and it was received at 33mm, that 31-33= 2mm BO (base out) because the received PD is larger than the PT PD. In the OD the prescription is a minus lens (-) when the RX is minus we change the base to the opposite direction, in this case meaning BI. If the RX was in a plus lens (+), then we keep the same base direction meaning that our base would stay as BO (base out). Hope this helps! Great videos, I am refreshing my memory for my BOARDS!
My coworker and I screenshoted the picture of the man who sat on his glasses LOL! So good. And great, helpful explanations as always - thank you!
Thank you!!! Prism has always been super difficult for me to understand and I really struggled with base directions! This video really helped me to understand this! Thank you so much for taking the time to do these videos! They are absolutely wonderful and you actually make them interesting to watch. Keep up the great work and again I can't thank you enough!👍👍👍👍
Hi John love your work and your videos and am currently studying to become a licensed optician dispenser however, m having trouble with the first example. At 3:30 how did you get 0.25? For the -2.25x0.25= -0.56 equation
You need to start with the first video and work your way up to this part II one. It has to do with where on the lens the power is. We cover the optical cross, 30-45-60 and then PIOMF first.
At 21:11 OD follows the -1.25 x 0.25 = 3.13 formula, but on the OS would it not be the same? OS -1.50 x 0.50? Im having a hard time figuring how you got 1.63.
can you explain how he got 3.13 because i am having difficulty I keep getting .31
Me too! I'm lost
Hi John, at 24:00 you say that the correct answer is 1.4 BI R, 1.4BI L. I'm getting confused because 1.4 diopters is how much total prism is induced (0.9 in R and 0.5 in L). It almost seems like you're saying there's 1.4 diopters in both eyes. Could you please clarify why you would write it as you have? Wouldn't you just say 1.4 diopters base in R, since the R eye has the greater power??
Follow the rules. If prism compounds it is written one way if it cancels it is written another. OpticianWorks.com.
At 5:00 where do you get the .25 and .75 that you are multiplying the cylinders by?
Hey John, your videos are extremely helpful! Just a quick question. At 12:09 you mention the final answer of .5 prism diopters in the left eye, but left out the direction. Would having the direction make the answer wrong? Thanks so much.
Rom, Great catch! You are 100% correct the complete answer would be 0.5 diopters BASE OUT in the Left. Sorry that IN is misleading and the direction is missing there. Next time! John
I’m so happy, scrolling and someone did CATCH it too, before I go crazy and commenting it’s wrong!!!!!
I’ve been watching all the videos up to here, and I may have missed it, but are powers weakest at 180 and strongest at 90? For 180, you take a reduction based on the cylinder to the power on the prescription, and at 90, you add based on the cylinder to the power of the prescription?
You need to start with this one and work from there: ruclips.net/video/T7em2JP3zWI/видео.html
@@LaramyKOptical thank you funny enough after I posted my message I went back and re-watched the first couple of videos and definitely understood it better the second time around. Thanks!
What here the factors/ resaonn that give you 0.9 and 0.5??? I was understanding until they appeared
Wait were they rounded to the nearest 10? .90=.93, .50=.48 ?
@@KingsKnightNumbaTres I don't find exactly where that occurs but, yes, that is the most likely answer. I'm not very good with math and a very sloppy "rounder upper-downer." John
Hi John thank you for your helpful videos.
About the Danika’s and Jamal’s on the left eye at @180 I don’t understand why is 1.63. The rule is not -1.50x0.75 that is 1.13?
Thank you
Renata - You need to work the rule all the way through. As I mention in the video you should have watched the 30/45/60 rule video before starting this one. -1.50 X 0.75 = -1.13 which is then added to the sphere power of +2.75 for a result of +1.63 total power in the meridian of 180. It is the combination of amount of cylinder in play combined with the sphere! John
Patients right eye = OD / Patients left eye is OS (12:07, answer is .5 D out OS)
See comments below please.
Hi Sir, thanks a lot for your lessons that are extremely helpful for newbies like me. I have 1 question at 10:23 of the video. I couldn't get it why 0.2 x -7.56 = 1.51, shouldn't it be a minus result as -1.51? I know I miss something to understand it. Could you please help?
Prism doesn't have a sign only an amount and a direction. You need two prisms together to create a focal point or a positive or negative vergence of light. Prism is only about the perceived shift in position. John
Thanks much!
24:19 - I think the way this should be written is 0.9 prism BI OD and 0.5 BI prism OS. The reason why is the way you have it written, 1.4 BI OD and OS, that gives you a total of 2.8 prism diopters. The answer needs to show how much prism is induced in each eye individually. Each eye induces different values (0.9 and 0.5) not 1.4 in each eye.
You need to follow the rules for compounding prism not cancelling prism. Those are two different rules. John
@@LaramyKOptical Yes we did do compounding prism. 1.4 BI would be the right answer if it said 1.4 total BI prism OD or OS only.. if you say 1.4 for both, that gives a compound total of 2.8 which isn't the total. Am I thinking of this wrong? 0.9 total BI OD compounded or added to 0.5 would give you 1.4. But TOTAL, not 1.4 for each eye individually.
The rule says, Compounding: Write the result as total amount in both eyes with direction for each. 0.9+0.5=1.4 for a total, total in each eye 1.4 expressed for both the R and the L. The answer as written @ 25:09 in the video 1.4 BI R and 1.4 BI L is correct. I'm not sure why you want compound it again? It is already compounded when you add 0.9 and 0.5. ?????
As an optometrist, if someone wrote a glasses prescription with 1.4 BI OD and 1.4 BI OS, that would be a total value of 2.8 prism of BI. The total amount of induced prism in this problem is 1.4 BI. So I think our confusion is are you saying 1.4 BI OD 1.4 BI OS is the same thing as saying “the total amount of induced prism in this pair of glasses is 1.4 BI”?
@@eyeeric9686 I'm really not sure what to say. That video has been up for over two years and has had 11,000 views. That example is also used in the ABO prep questions which have been taken over 7000 times and no one else has had a problem with it. The answer as written to the rules is as shown. I don't think the idea behind it is to say your result is any way equal to or the same as the amount of prism you desire. In fact the exact opposite. So it wouldn't be written that way. ????? The answer to how much ERROR was created is _____________. Not the answer is equal to this prism notation on a written prescription would be _______________. ????
Do you prefer this prentice formula over ◇= Dd / 10 ??
No I sure don't because it isn't what we were taught and what I am familiar with. I'm sure if it was I'd like it! ;-)
@LaramyKOptical I gotcha'! I was able to follow your way just fine but that's how we were taught in school. Looking at it, do you think there's any negative going with that one rather than yours? D= power X d= decentration and answer divided by 10? Thank you
@@erodas8899 Either one is fine and either one will provide the same consistent results. If it works (for you) don't fix it!
Hi John,
In 23:22 wouldn't the prism be BO instead of in? In your part 3 video you use a similar diagram and say it is supposed to be BO as well. By the way your videos are helping me so much for studying for the ABO test.
Morgan, Mmmmmm... if you freeze the video at 23:22 it can't be much clearer. The red dots are the lens OCs and the black dots are the wearer's pupils. Both those OCs are IN towards the nose. The base of the prism is IN for both eyes. You are only looking at the single triangle that the pupil falls within. Don't look at the "lens" look at the prism. John
I understand now thank you!
It is soooooo easy to get confused... whenever I get a question like yours it takes me a few minutes to work through it and get it all again myself. The only thing worse is compensated powers! John
Sir what is the use of those spectacles lenses which were made away from optical centres and have these prismatic effects.
Osaf,
When it is done deliberately it is to correct a problem in the way the brain and the eye see things.
Maybe the right eye sees an object where it actually is.
But, the left eye sees it 5cm over from there.
You can use the image shift to bring the two together.
I have more about that in the other videos and much more on the website.
John
Ok
Waiting for next videos.
How to get Standard optical centre???? If they said there is a prism has been induced???
Thank u Sir
opticianworks.com
Thank you for your lessons
I need extra explain
2:26
How come 30degree change into 0.25
And 60degree turns into 0.75???
it's the 30, 45, and 60 rule. John has a video to explain that.
You can also use another formula subtract axis from 180. 180-150=30.
Cyl -2.25sin(30)squared. 2.25sin(30)2=0.5625
Then add sphere +7.00= 7.56
Then multiply by by the Pd error 7.56*0.2=1.5 prism
Nexx1, That would be the power in oblique meridian formula and that is covered in a later video lesson. Baby steps, baby steps. baby steps...
Hi I have question for you I am student optician I need some help I dont have hands on experience are u gonna help me
OpticianWorks.com
at 18:02, left eye, how is he looking through BD prism? I am so confused here.
Now I'm confused. It is shown/drawn on the whiteboard. I'm guessing you are missing both the concepts of lenses as prisms and orientation 180 or 90? Or you are missing the entire process of determining error. This isn't one of those things you can sort of pick up in the middle. I'd head here: www.OpticianWorks.com. John
@@LaramyKOptical i went back and reviewed the previous videos for a 2nd time and I think I figured out what I was missing. Thanks for building such a helpful channel for opticians!!
@@LaramyKOptical so im going back through the previous videos and feeling confusion as well. to be specific, what was the determining factor for drawing the different shape on Left eye? I realize that the lens moved down because the OC moved up and now has a positive number. why is one lens the hourglass shape and the other is the diamond shape... Im missing that deciding factor somewhere...
I think I figured it out...is it that the hourglass shape is associated with the minus lens power. and the diamond shape is associated with the plus lens power? It is the same for moving along the 0-180 horizontal space too...
Had a tricky question in my ABO exa. Pt have an RX at +1.00 -0.50 x 180 OU, if looking at 5mm above the OC, what prismatic effect will the pt experience? Base in? Out? Up? Or down?
Still plus at 90. Above the OC in a plus would give you BD. If in doubt draw it out... Did you complete the OpticianWorks program?
Sorry but did you mean BU??
HELLO!!I BECAME FAN OF YOU AND YOUR VIDEOS,YOU HELPED ME A LOT!!!WELL I HAVE THE QUESTION AT THE PREVIOUS EXAMPLE...WITH THE CANCELLING EFFECT,YOU SAID AT THE END 0.5ΔINL,BUT THE BASE WAS OUT....WHAT I MISS????THANK YOU AGAIN!!
You may want to consider a membership to the OpticianWorks.com program. Plenty of additional examples and step-by-step stuff there.
The videos you present are outstanding sadly many opticians have to learn this way as formal training is not required to claim the title of optician. I believe that Prentice rule (that is why it is a rule not a law)does not produce the correct amount of prism in cases when the axis is other than 90 or 180. An example would be +1.00 -2.00 x 45. The power would be 0 at 180 allowing any pd to be acceptable. That is not the case you induce up or down prism depending which way the decentration is off. Put a lens in vertometer and move to observe the result. To actually understand the amount of prism induced you have to calculate the induced prism in each primary meridian and calculate the resultant prism. In this example the resultant prism would be at 90 giving you up or down prism depending on the direction of the movement. Your instruction is a rule of thumb that will most often produce an acceptable answer but one must understand when it will not work at all. Few opticians can calculate crossed prisms so it would probably be easier to get the result mechanically in the vertometer.
very nice educational video thank you.
is there a video that shows the optical triangles for base out and base in between minus and plus scripts?
YES!
Watch all the videos that are dated before Prentice's Formula Part II.
You label the left eye with the R measurements....
The solution I offered in my previous post here about a week ago (regarding your 2nd example in this video) was incorrect. I have deleted the post. I have since verified that your answer is correct. I apologize.
I have since corrected my own methodology (a bit different from yours and retaining, and making directional use of, the +/- signs throughout the solution process). Sorry for any waste of your time and consideration. I do appreciate and enjoy your videos despite being a non optician layman.
Well what can I say Joe but THANKS! John
is awesome for Jamal and danika
Degrees = % of cylinder power
030 = 25%
045 = 50%
060 = 75%
090 = 100%
The % rule is covered in another video after this one - take things in steps. Prentice's Rule is for 0-180 and 90.
Svp traduction en français
Lmaoooooooo 😂😂😂 fox channel