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Use the Prism Compensation Device on the instrument. Put it in the meridian you’re looking for and dial in the number of prism you need. Then center the glasses like normal. (Very simplified explanation.) For example, if you need to verify 10^BU. Then you’ll orient the PCD in the 90 meridian and dial in 10^ BD. Turning it so the power lines move down, then look at the numbers on the dial until you get to 10^. Ideally, if the lens has 10^BU it will cancel the 10^BD you dialed in and powerli es should center at target center. Any variation means you have some undesirable difference. Note, you still need to follow other power rules to ensure strongest lens is centered first and any undesired effect is measured in the weaker lens (2nd lens).

The exact same way, except it’s the point where the spher and cylinder cross. You need to toggle back and forth between the two powers until they both align with the point you need to place it or read it from.

Wont the centre point of the grid be blurred in case of a spherocylindrical lens?

@@anweshamaitra3130 you still orient the axis and get power in focus, you just move the center power cross point (the base of the prism) to the point needed to position the prism desired.

I would need more information to help you sort this out. The prism application in this video deals with SV lenses but it's essentially the same procedure when it comes to checking the distance power and unwanted vertical prism in a segmented lens. Essentially, you should be able to perform the measurement of prism error and apply tolerances the same way.

Merci!

Translated via ChatGPT: 1. La centrage joue un rôle dans la sélection du diamètre des verres. 2. Le diamètre de la lentille recouvre l'ouverture de la lentille avant que la centrage ne soit effectuée. 3. Après la centrage, ce diamètre de lentille n'est plus suffisamment grand. 4. Laisser un espace dans la monture qui ne correspond pas au "découpage". 5. Lorsqu'un bloc plus grand est utilisé... 6. ... la lentille est suffisamment grande pour couvrir l'ouverture avant... 7. ... et après qu'elle a été décentrée. 8. Il n'y a aucun espace dans la couverture de la lentille. 9. Et la lentille est découpée et peut être utilisée. 10. Merci d'avoir regardé.

Thanks for commenting. I’m glad you find them helpful. Hopefully I’ll have time to upload some new ones this year. Good luck on you boards!

You’re welcome. I’m glad you found it helpful.

I’m not sure I know what you’re asking for. I don’t have a PDF version of the lecture. My students have online content and worksheets in the course they have. This lecture was based on that content.

thank you for your response @@MsTracyBennett

@@hanifidemir8075 you’re welcome. Sorry I couldn’t be more helpful.

You're welcome! I'm glad it helped you!

You're welcome! Knowledge is empowering. Keep learning! Great field to work in.

Thanks for your feedback. I'm not too proud of it myself, but I won't take it down until I've made one that covers the info. It was created for one student but I posted it at a request from other students who wanted access to it. It was also one of my first videos. Sorry you disliked it so much.

Q1 - I believe so but the rings should be marked (similar to the target in this video). [Here's an example image that has 1^ as the first ring. www.reichert.com/products/ml1 --> this one uses the inner hash lines to determine where the 0.75, 0.50, and 0.25 are on the target. The ABO Practical simulation "Tutorial and Practice Exam Question Area" discusses how the central target is broken down on slide 24. www.abo-ncle.org/ABO/Exam_Information/Practical_Exams/Practical_Exam_Tutorial/ABO/Practical_Exam/Practical_Exam_Tutorial.aspx?hkey=b53962d8-5427-4cf4-9cd7-2074c6c91d9c] Q2 - Prism is measured/checked at the prism reference point (dot below the fitting cross). Distance power is measured/checked at the distance reference point (circle above the fitting cross). The fitting cross is used only to measured placement in the frame (measuring/checking that the fitting cross corresponds to the wearer's monocular PD and fitting height). This is a good reference that has some good info and pictures at the end that show how the lens should be centered to verify the various aspects of a progressive. aamerniazi.blogspot.com/2014/01/measurement-and-dispensing-of.html. Hope I answered all your questions! Let me know if you need clarification on anything or if you have any new questions.

If you have trouble accessing the "ABO NCLE Tutorial and Practice Exam Questions Area" it can be found on the ABO-NCLE website under Exam Information. Select Practical Exams, then Practical Exam Tutorial. The link is in the text shown on the page. Once opened, select "Mastering Lens Meter Simulation" and go to slide 24 for the measurements of the inner 1^ ring. (ABO-NCLE website www.abo-ncle.org/ABO/Home/ABO/Default.aspx).

@@MsTracyBennett wow! Bless your soul for being such a helpful person! Wish we had more of you in this world🙏🙏🙏 Im now clear about question 2 and thanks again, but even after checking out your link, Im still confused about our lensometer only having 3 rings (and no labels or numbers on them). If prism is showing on first circle (first inner circle), is this a 1 Diopter then?

@@libra8194 Do you know what kind of lensmeter you have? The brand or style. That might help me provide better direction. You can also examine the distance between the circles that you do have, and examine the distance from the center of the target to the first ring. If the ring distance is the same as the distance from the center to the first ring, then the first ring is 1^. If the distance from the center to the first ring is half of the ring distance, then the first ring is 0.5^. I would be willing to bet that first ring on yours is 1^.

@@MsTracyBennett you are 100% right! It is a 1 prism (the first ring) these spaces are all the same, between 1,2 & 3 and also from centre to first ring. Many many thanks to you!! God bless ❤️❤️❤️⭐️⭐️⭐️

Glad to hear it! Thanks for letting me know.

Best of luck to you! We need more licensed opticians!

It’s a surfacing step that reduces the blank diameter to the diameter called for by the pair. Crib diameter is equal to the minimum blank size. Let’s say the manufacturer offers the blank in a 75mm but the pair actually only needs 58mm lens. If surfaced, the lab can remove the extra material (aka crib it down) to reduce the size to 58mm. When the surfacing lab cribs the lens to reduce the diameter down to the minimum blank size on a plus power lens this allows the lens to be generated as the thin as possible. On plus lenses, the diameter directly impacts final thickness. For minus lenses it just helps reduce edging time and wear/tear on the edger.

@@MsTracyBennett very clear explication thank you👌if you don't mind I have another question and what's cross curve ?

@@Jay51192 cross curve is the curve on the lens (usually on the back) that creates the cylinder power in the prescription. The cylinder power is the part of the prescription that corrects astigmatism. My video on Nominal Power can help explain it in more depth.

@@MsTracyBennett thank you for the explanation I just started a job in optical lab in surfacing and trying to learn about it and about informations that we put in generator to create the lens.

That's great! Welcome to the club! Feel free to contact me with questions. I love to educate!! :-D

Thanks! And I agree; in hindsight the background music was a mistake. Feel free to subscribe so you’re notified when I post new videos.

Good luck on your next attempt! You got this!

Me too

When you center the power lines at the center of the target and spot the lens - you are spotting the OC. The horizontal distance between right and left lenses OC is measured and compared to the wearer's PD. If you don't have an order ticket to compare it to or you don't have it... then just measure the wearer's PD and continue the testing method as described to determine if it meets tolerances.

@@MsTracyBennett Yes, after consulting with a couple of people, sounds like I'll have to have them put them on and spot their OC's and go from there. Thanks for getting back to me!

I’m working on it! I teach optics in my full time job but I’m working on adding more videos to their content. Thanks for the encouragement! I’m so glad the videos help you.

Hey Tran! Prentice can be used to calculate the prism effect based on the millimeter error and the power of the lens in the horizontal (180) meridian. However, the calculations are not as exact a measurement as moving the lens in the lensmeter to induce to 0.33^ in each lens. If you use the calculation method - keep in mind it generally over estimates the prism amount. Let me know if you have any other questions. Thanks for the feedback!

Hi Tracy, thank you for your answer. Yes I have one concern.. When we finish neutralizing, dot the centre of the lenses and measure PD of the first pair. You move to the second pair with out moving the table and then you realize that the second pair is having some horizontal prism. How do you know what prism it is when you only have a prescription from the doctor and you are trying to find out what the lab made...?

@@tranthu6889 when the dr prescribed prism you need to center the lensmeter power lines at the location where the prism is displayed. Ex: Rx has 2^BU in OD, then the lines are centered at 2^prism ring directly UP from the target center. Rx prism and unwanted prism are two very different things. ANSI is applied to error in Rx prism in a similar manner to non Rx prism lenses. The only difference is where original reference point is (the OC or the Prism Ref Point).

You’re welcome! Glad it helped!

MIC upgrade!! Well worth the $30! (Boya)

Only when you are calculating and determining stuff on paper. In the lens meter you just move the lens in what ever direction you need to make the base direction correct. It will be opposite movements of the lens for plus and minus powers but the base direction in the lens meter is the same. Right lens base in is illuminated target to the right and out is to the left. It’s all about the location of the patient’s nose.

I just uploaded one tonight on this. Hope it helps!

Not when you're using the lensmeter. The illuminated target is the base of the prism and the center of the target is the wearer's "pupil". What you need to know to determine base direction - is the location of the wearer's nose (which eye we are working with). The base direction is what it is when it comes to the lensmeter. For a right lens (nose is on the right). If the illuminated target is right of center there is base IN prism. If the illuminated target is left of center there is base OUT prism. - What you're thinking of is the actual movement of the lens... this will be in opposite directions for plus and minus powers. When using diagrams to examine prism, you will need to know whether the power is plus or minus, but this is not needed when working with the lensmeter. The power of the lens (plus or minus) needs to be used when you're determining base direction using schematic drawings. For example, the OC is displaced 4mm out/temporally from the pupil, what base direction will the wearer experience? In this case, you'll need to know the whether we are dealing with a plus or minus lens power and whether it's the right or left lens.

Thanks! I'm glad it helped! The way I see it, you measure the prescription first. During the process of measuring the prescription, you will identify and measure any unwanted prism. You're kind of doing them at the same time. Prescribed prism works the same way. The only difference is that the illuminated power lines will be centered at the prescribed prism location and not the center of the target.

Glad it helped!

That's great to hear! It really isn't that difficult once you get the hang of it. Dare I say, it even becomes pretty easy.