Colleagues,
A quick poll/question.
We we all know the importance of OC heights for VA. At which point would you steer your patients away from a particular frame choice? My rule of thumb is 5 BOC.
Seems that in the new world of compensated choices, I’m seeing serious deviations from this.
Thoughts?
When you say steer away from a particular frame, do you mean due to thickness issues or optics issues?
Both. Especially with PALs, when the distance is partially cut off.
In wearer studies, we generally require a minimum of 10mm above the fitting cross- to allow a sufficient distance area.
Pete Hanlin, ABOM
Vice President Professional Services
Essilor of America
http://linkedin.com/in/pete-hanlin-72a3a74
Agreed. Not to mention the difficulty in reading an RX correctly when the frame doesn't allow for a perfectly perpendicular contact on the lens stop.Originally Posted by Pete Hanlin
My general rule of thumb is 10mm min for the top, 14mm min for PAL seg or 10mm for bifocal seg. If someone comes in wearing 8 or 9mm on the top, I will let that fly.
Have I told you today how much I hate poly?
Keep it 8-10 mm above the pupil height for best results.....
I like to turn it up to 11.
Edit- once or twice a year I get those just used to the 5mm above, similar to those that would fist fight me if I didn't drop their segment 5 mm below center.
Either I'm not part of everyone or I can't figure out what your referring to. Care to expand on these statements?We we all know the importance of OC heights for VA. At which point would you steer your patients away from a particular frame choice? My rule of thumb is 5 BOC.
Also why are you cutting part of the distance portion off?Both. Especially with PALs, when the distance is partially cut off.
Part of the issue is that we manufacture eyewear for opticians that feel that 10 BOC on a SV is perfectly fine, and then complain about the thickness. Just last week, I had a pair come across my desk that had the OC @ 5mm from the top of the frame. 11mm vertical decentration on a -6.00 FFSV.
If the fitting triangle were to be used as a guideline, then many of these ill fitting frames with high OCs would not come across my LMS. I just wanted to see what other opticians here feel is OK before guiding their patients away from such frame fits.
It's not unusual that we see 30 SHs on a 38B frame. The feedback I get when I put these on callback, the patient wears the glasses low on their nose. No thoughts on the keyhole effect, no adjustments for the VD. They say run it, so we do. I stopped putting them on callback, since I know what the optician(s) will come back with.
Got it. I can infer what it means from the context, but what is BOC stand for. I have never heard that abbreviation on the retail side of things. I see why you are cutting the distance off now. Sorry, I forgot you were on the wholesale side. Cutting the jobs, not measuring the seg heights.
I get what you are saying, there are plenty of "opticians" who don't think twice before letting a customer pick their own frame and ship the order off to the lab. I'm not saying I haven't occasionally done things like this. Because no matter how hard you try, some patients will just demand something that is ill advised. Sometimes I just flat out won't take the job and let them be someone else's headache. But, if it is a long time patient and I have sufficiently warned them, I won't turn down their money. Every situation is going to be different. I can think of a handful of patients who do wear their glasses at a 20+ vertex distance. I have tried to correct the fit and segs on a few. It did not go well. No matter how you fit the frame, they will find a way to push them to the end of their nose. If the lenses don't work like they are used to, even if it is not optimal by the book, they aren't going to be happy. So, I make them "incorrect" glasses they are happy with.
As far as accounts complaining after ordering a job, I can only think of a couple options. If it is not hurting your bottom line, I would just suck it up and ignore it. No reason to rock the boat if you aren't losing money. It is a pain to work with untrained, unqualified people, but that's the way of our industry now. I get phone calls all the time from vision works and the like asking for material, PAL design, seg heights, PDs, etc. of patients previous glasses because "we just can't seem to get it right". If you have too generous of a remake policy, you may be losing significant time and money on these jobs. So, you will either have to find a way to train your accounts(good luck), or establish a new, less generous, remake policy. If it is really costing too much time and money, occasionally you have to politely fire customers.
To your original question, I don't really have a rule of thumb per say. It is going to vary with previous glasses, Rx, index, mounting type, Lens design, head size, how badly the patient wants the frame, etc. I also do all of my own finish work and only order uncuts, so I have a pretty good idea for what the finished pair is going to look like when I'm working with the patient.
New to me too.
http://www.pechoptical.com/userfiles...%206_23_10.pdfThe distance between optical center and top of segment.
We should choose frames that keep the pupil heights from 3mm to 6mm above center, with the center being the datum/180 degree line, the midpoint between the boxed topmost and bottommost part of the lens. The optical center might be coincident with the pupil height, or more likely at some point below the pupil height, depending on the lens design and the degree of pantoscopic tilt.
Best regards,
Robert Martellaro
Science is a way of trying not to fool yourself. - Richard P. Feynman
Experience is the hardest teacher. She gives the test before the lesson.
OK. I'm aging myself. BOC was introduced to me by my wise lab manager sometime last century, just before PALs came out and STs were king. Segment (B)elow (O)ptical (C)enter. The term stuck in my head. We used it as a reference to all OCs. I still hear some old timers refer to it as BOC.
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