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Marking and Measuring OC Heights
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- Опубліковано 15 сер 2024
- Let's talk about preparing for, marking, and measuring OC (optical center) heights. When is it necessary and what are the rules of thumb?
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Your videos have been so helpful through my first year of working toward my opticianry degree!
I just started at visionworks as a optical specialist this is a field I have never been in so everything is like a foreign language lol but im starting to understand
David thanks for your fruitful videos,wish you the best
Very useful information! Thank you
When measuring oc or seg height are you going from were the lens meets the frame or halfway into the frame thickness (where the lens sits in the frame itself).
Good video.. if you use pd Meter for pd on asymettrical frame the OC heigh Can Little change...
@12:36 when you measure her, you are about an 1.5 inches below her eyeline. You are looking up, and she is looking down with her eye, though head is close to bringing frame perpendicular to the floor. OC should align with OA. My opticians keep missing this and due to Panto, causes the upper part of the lens to focus short and distance to be only one small area below the OC. One can apply Martin's rule or just have the patient sit so the chassis is perpendicular and optician is exactly at pupil straight-ahead gaze.
If your opticians "keep" missing this perhaps it is time for an OptiKam Pad or another electronic measuring device= problem solved. I've fit/dispensed tens of thousands of glasses and never once lowered an OC height - ever. Your "upper" part "lower part" makes me think you are confusing OC and fitting height which are not the same thing. Martin's Rule which I completely disagree with wouldn't apply to a progressive where you fit to cross or use a free form and POW measurements.
@@LaramyKOptical Thank you so much for your response. I've learned so much from your videos. I have flat lenses with bifocals, not progressives, so no confusion. Do you disagree that the OC should be perpendicular to the eye's optical Axis? It would have to be lower IMO to compensate for panto tilt and angle; otherwise, upper part of "flat" lens will focus short on retina, and lower part will focus long past retina. I'd love to send you my diagrams. I'd love to get my situation resolved as I have been dealing with it for over two years and opticians keep getting it wrong and the doctors don't want to intervene. I found an optician who grinds his own lenses and he nails my axis whereas the boxhouses could not. As a photographer I have a critical eye and focus is paramount.
OD -2.25 +3.25 114
OS -3.00 +4.25 76
I also have considered that my CYL is overcorrected which is adding to the super sensitivity to the geography of the lens. I have a 9 year old pair of glasses that are:
OD -2.50 +3.00 111 (+4°) (axis on old is wrong, so adding 4 degrees for current axis)
OS -3.75 +3.75 75 (+1°) (axis on old is wrong, so adding 1 degree for current axis)
When I add a 1.00 reader on top of that, I have clear, focused, relaxed vision. I realize the +1.00 add on SPH is equates more to +1.25 SPH since it is on top of lens. This would make the RX:
OD -1.25 +3.00 114
OS -3.50 +3.75 76
So, when I compare that to the original RX, the CYL has dropped .50 diopters, and the SPH has increased by .50 diopters.
Thanks for your feedback! :)
@@b.larson3151 When you said "my opticians" I assumed you were a doc or manager - my bad. Do me a huge favor and email me through the OpticianWorks website. Much easier for me to deal with stuff like this through email. Thanks John
Love this guy
Love you too.
Do larger nosepads help for those without much of a bridge? I've been curious about that since there are different sizes available and my optician usually just puts on what they feel like. I guess larger ones don't look as good cosmetically.
They certainly can help. A fresh set of silicone pads really grab well for at least a few weeks. You can get a little refresh by wiping them off with an alcohol pad. BUT - it is more about overall frame fit. For those with little or no "bridge" at all fitting can be quite difficult. And yes smaller pads do tend to look much nicer than larger ones do. They run from 5mm round buttons up to 21mm traditional. If it is a constant battle or task specific there is always contact lenses.
@@LaramyKOptical Wow 5mm nosepad seems super tiny.
What about OC height calculations? I was taught first to dot pupil center. Then, determine half the B (the GC). Next, determine the difference between the GC and pupil center. Set the OC to be half way between the GC and pupil center. For example: Frame B = 40mm GC= 20mm Customer is at 28 mm. Then, the OC should be 24 mm. Thoughts on this? Ideally, someone should not go with a frame that they sit that far away from the GC.
As always - If something works well for you with consistent results then keep doing it. That sounds like a great rule of thumb technique. I think I'm basically saying the same thing or it would work out to being the same. John
My prescription is -6/-5.75 with -1.75/-2.00 astigmatism.
My question is for this type of Rx, what would be the margin of error for OC measurement (in mm), considering the lenses that I am getting are free form.
I am concerned that the optician might not have taken very accurate measurement of OC.
Very little. See the 3 videos on Verification & Final Inspection. Anything under 5 it is not that important so that right eye of yours needs to be spot on.
Hey, just got a question about the OC not being 1-5mm off from the centre, which is a great point. BUT, in our practice, we get heaps of Asians, and the fashion trend with glasses lately have been oversized frames it seems. And when oversized frames + high myopes + little to none existent nose bridge combines all together, we often have to shift the OC by up to 10mm. They are very fixated on that particular oversized style, and we have no choice but losing customers if we don't dispense these oversized frames.
What would you do or what would you say in these instances?
Heck what are you going to do? You tell them, show them, discourage them, explain why it is a bad idea - but they insist so - take their money. In those cases you do what you have to do. You can't fix stupid. Keep in mind that what matters is that the OCs are on the same plane they don't have to be perfectly aligned directly in front of the pupil. With a shift of 10mm you may be getting into cut out issues in the vertical and horizontal = yikes! Make sure you note what was said so when they come back 3 weeks later complaining you can say, "I told you so." Of course 3 weeks from now micro-glasses may be all the rage and problem solved. And of course anyone can wear contact lenses so maybe they want to try those and then those dinner plate specials in plano? John
@@LaramyKOptical Hey, thanks for the great reply! I was just wondering what you personally think is the best digital measuring device? We currently have the i-Terminal mobile from Zeiss, but have found it to be quite inaccurate. Your opinion would be much appreciated! Thanks :)
@@ansonlee5014 I don't have much experience with any of them but the OptiKam Pad is pretty user friendly and has great support. I actually regret not using one enough to get good at it but we didn't have one where I worked.
I got a problem for you, david, so bear with me, you mark the center of the lens with lensometer, then you see its not at the physical center of the lens, so in order to fit the lens in frame, you need to turn the lens 180 degree( you know when you turn around the lense 180 degree, the cylinder power and axis stay the same)
But for good measure , i marked the lens again, turning the lens around 180 degree, thinking it would overlap, but it didnt, i tried other lenses, it was the same story, the optical center would be off about 1to3mm from the first marking depending on the lens youre using,
I do know exactly what you are talking about with the displaced OC and rotating the lens. DOH! I hate that.
As to why it would shift the target in the lensmeter I can't say for sure. Since the OC is an actual thing I would guess that any shift in the target in the lensmeter would be down to lens angle. Once you rotate it and it is sitting at a different angle relative to the lens stop you may get a shift in the target. Effective power/lens tilt stuff. You usually don't get into displaced OCs until you get into higher powers which is where effective power/lens tilt stuff comes into play.
My hunch would be higher powers and certainly higher cylinder would create more shift?
Would be interesting to see what happened in a high end auto-lensmeter and dual lens mapper.
Really not much you can do about it so I wouldn't let it keep you up at night.
As a glasses wearer I feel that opticians (the ones I've bought glasses from) can't get the frames level when I "complain" about it - my first hunch was that maybe my ears are not at the same height and I'd adjust temple angle from hinge area so that the left or the right side of the frame goes up or down, but I've only seen them adjust nose pads.
NOPE! You are 100% right. To level a frame you angle the temple at the chassis! And yes most of us are a bit asymmetric and some us are very asymmetric. There are even several tools designed specifically to bend the temples in the proper way to level frames. Best not to stress the hinge much but if possible to get the bend done just ahead of it where it bends to meet the chassis or frame front. Find a better optician! John
I noticed the reference to using "the phone book" if necessary to get the optician to the right seating height. I'm old, so I get the reference. I wonder how many opticians in the under-30 demographic do.
LOL yeah. Should have said pillow. And of course a rural Maine telephone book was all of about a 1/2" thick where a Northern NJ book was 6" thick. Yep - I'm old!
What about compensating for
pantoscopic angle?
There are several videos on compensated lens design and lens tilt.
Thanks, is it possible to know which application you have used with the Tablet?
OptiKam
I use the digital device to measure OC heights and always get a results of 2 numbers just like in the video. So which one should I better go with? 🥺
which digital device did you use?
Question, I’ve noticed a lot of younger customers wear big frames and like to wear them low on their nose. We always suggest that they wear them higher, but the style is big and low
As the saying goes, "You can't fix stupid." Followed by, "If I made you wear glasses like that you'd have a fit." Kids can't win.
@@LaramyKOptical😂
I was taught to use oc height for any rx if above the B. I can forgoe for powers under 5?
My opinion is yes skip the OC height stuff (for all reasons I mention) in lower powers. BUT - if you have been doing it forever and it works for you then keep doing it. There are no "rules."
ua-cam.com/video/el_EAEGSOZE/v-deo.htmlsi=8LqGYBq7rn6yV9gV
@@LaramyKOptical not forever, only 6 years. Have you found that oc height is helpful with toric polarized lenses though?
@@loristec3275 Certainly doesn't seem like a bad idea to do an OC for those. I can see how it might be helpful.
@@LaramyKOptical thank you!
I take OC lower due pantos of the frame what do you think?
I think that is an odd ABO thing. I never did understand it and I never will. The frame always gets a little panto - if powers are high and it is needed the lens gets a little OC bump. That's it in my book. BUT - As always - if it works well for you consistently then keep doing it. John
@@LaramyKOptical I came to ask this too- essentially every time I have ready about taking oc's, I've also read that you should lower it 1mm for every 2 degrees of tilt. So you don't necessarily recommend this? We actually had to remake a high minus as after the calculations the oc was too low and he could see better with it higher up so it makes sense to me that you wouldn't need to adjust it.
@@koibito55 I most certainly do not recommend following that rule of thumb. Again - I never have understood it - I never will.
I think it is a two-fold problem:
1) It is one of those persistent optical myths that people just won't let go of and the ABO perpetuates.
2) That it does actually have some relevant connection to effective power and lens tilt which might look great on paper but doesn't actually transfer at all to the real world.
The frame always gets a little panto - if powers are high and it is needed the lens gets a little OC bump. That's it in my book.
@@LaramyKOptical excellent. Thanks so much for the info!
Our patients that are in the 15-25 age all insist on large giant frames even if they have +/- 4. I hate some
Of the new trends. Doesn’t allow us to do our jobs correctly. They rarely listen when we say no.
Same boat with you and I'm in south east Asia. I just slap the lens in and call it a day. These young people don't really care about the clarity of vision but more to style.
Retail isn't easy! You simply do the best you can. If everyone at school is wearing the dinner plate specials they will want them too. Nothing you say or do will change that. I would suggest noting that you advised against them. I would suggest you learn how to promote contact lenses. Human nature isn't your fault! Deep breath in - deep breath out, relax. John