Fitting height compensation
New rimless line can mix and match lens shapes with frame color, bridge and temple size. Stock models are demos showing the various available lens shapes in varying size/color of chassis. Patient chooses the shape and frame color and you measure OC height on the demo lens with frame DBL of 16. Patient actually requires bridge of 18, which you intend to order. What's the rule of thumb to adjust/drop OC accordingly to accommodate larger bridge?
For this example, an adjustment of 0.5mm suggestedOriginally Posted by OptiLove
B
How did you arrive at 0.5mm? Is there a formula I'm failing to remember for this?
Perhaps I'm dense, but why would a DBL change affect OC height? In a stupid shape like an aviator I can understand. But if the lens shape is rectangular, a 1mm horizontal centration change per lens is unlikely to affect vertical OC at all, no?
Since pt needs a 2mm wider bridge, this would move each lens 1 mm temporally compared to demo lenses.
Why can't you just move one millimeter horizontally nasal from your measured OC and then take the measurement?
It should be a very minimal difference (if any) unless shape is unusual.
I’m following this thread, but I tend to agree with Barry. If fitting a 16 dbl, then changing to an 18, even with adjustable pads, the fit will drop Raising the prp by .5 makes sense. Less adjustments @ dispense.
I bend light. That is what I do.
I'm in the dense category.
You're assuming the frame will fit more loosely. I don't think that's a guarantee.
I think we are talking about two different things. The pupils didn’t move but the FPD did change so the inset must be recalculated for horizontal movement. Vertically the B measurement did not change changed but the fitting height on the nose should have dropped the frame somewhat. As Barry “suggested” .5 mm is a good starting point. I think paying attention to pantoscopic deviation is probably more important here.
Chris
Oh I think some are assuming larger DBL will also widen bridge fit, thereby lowering eyewear. My experience with rimless is primarily Silhouette, and on those the nose pads are identical on all bridge sizes, only the width of the bar that mounts the lenses changes. So in Silhouette or anything equivalent DBL and bridge size changes won't impact OC height.
Can you not swap in an 18 bridge from another frame into the frame used for measurements? What kind of frames are these? Also can you not adjust the pads wide enough on the 16 bridge to get the rights fitting height for measurements even if the pads are spread comically wide?
There is no "rule of thumb" for this sort of thing. But you certainly would not be dropping the "OC" from what you measured if you are going to order wider bridge. You may have to slightly adjust your Pupil Height HIGHER depending on how the frame fits. Are you ordering a wider bridge because the frame sits too high on the patient? How high? If the frame is sitting 3mm higher than you want it to, you'll need to raise the measured Pupil Height 3mm since the frame will be sitting 3mm lower with the wider bridge. If the bridge fits well but the lenses sit too high, adjust the nasal lens holes higher to achieve the desired fit and raise the Pupil Height accordingly. If the lenses sit well, but the bridge fit is too narrow, order a wider bridge and keep the Pupil Height the same.
Do the lenses need to move up or down for optical/aesthetic purposes? If yes, by how much and in which direction? Adjust your measured Pupil Height in the opposite direction by the same amount. If you measure a Pupil Height of 23 but you need to raise the frame 4mm for fit. Lower the Pupil Height to 19. Bridge size is irrelevant other than for nose fit.
Agree w/ DrK. In the high weeds of nasal morphology here. Unless I’m quite mistaken there’s no abstract/statistical approach more efficient than just fitting the patient. If that’s not feasible for whatever reason, best to be meditating on the individual patient’s nose as to how greater nosepad displacement affects fitting height.
Unintended consequences abound: does the drop cause the lenses to hit the cheeks? Is a vertex adjustment feasible? If the bridge is like the Silhouettes I’m familiar with, that requires a rotational motion unavoidably affecting lens height as well—pushing off cheeks & clearing eyelashes will drop the lens further.
(Odds of Barry still being correct for some reason: 14:1)
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