Real world POW

[lerral]

How do you determine the true POW during fitting, i.e. the position at which the lens will come to rest after nasal geometry, perspiration, body oils, and motion dislodge it from where it was first set on the face? Are there any tricks to determine this natural POW? I'm not talking about sports or other extremes, but the difference between where a patient will initially put on his frame, and the place where a frame will naturally want to come to rest. I've found they're not necessarily the same.

A patient with OD -2.75 -3.00 002 OS -2.5 -2.75 180 add +2.25 chose a snug fitting 46-24-150 retro frame and was fitted with Shamir Auto II fixed 18mm in 1.60 material. On delivery he loved them but returned the next day claiming the reading power (and intermediate, it seems) was "too low". On a hunch I asked him to spend an hour doing ordinary activities with his glasses on before coming to see me again. I told him not to re-adjust the frame position unless necessary for safety. When he came in, I measured and marked the OC. I then asked him to take his glasses off and put them back on in the same position as earlier in the day. I measured OC again. There was a full 3mm difference between the two OC positions, more than enough to be very significant in his rx.

[rdcoach5]

Try adjusting the frame before taking seg height . Make sure you are at eye level and raise their chin if necessary. I have solved the very problem you describe by re-making in a short corridor. Spot the demos with a felt-tip pen and then double -check if that is dead center on pupil. ETC.

[lerral]

Thanks for the reply. I do adjust the frame of course.

I hope I'm explaining this clearly. I've learned that it is not easy to determine where the frame will come to rest on the nose after it is put on and then worn for some period. The natural tendency seems to be to set the frame as high on the nose as possible. But that may not be where the frame is stable. My own SV glasses seem to naturally sit a mm or two below the highest place I can put them on, similar to the PAL rx in my post, except that my rx isn't strong enough to make the minor position difference so crucial.

So, how do you determine a patient's natural position of wear, i.e. the place on the nose where a given frame is more or less stable?

[rdcoach5]

Thanks for the reply. I do adjust the frame of course.

I hope I'm explaining this clearly. I've learned that it is not easy to determine where the frame will come to rest on the nose after it is put on and then worn for some period. The natural tendency seems to be to set the frame as high on the nose as possible. But that may not be where the frame is stable. My own SV glasses seem to naturally sit a mm or two below the highest place I can put them on, similar to the PAL rx in my post, except that my rx isn't strong enough to make the minor position difference so crucial.

So, how do you determine a patient's natural position of wear, i.e. the place on the nose where a given frame is more or less stable?

Some people naturally hold their head high, some naturally or phyisically are unable to. More often in the office a patient will tend to hold their head lower than they normally do -just because they are in the office. I ask them to move in and sit the way they do while driving a car. Some shorter women do hold their head high to see over the steering wheel and you can spot this after asking them to assume a driving the car posture. Experience will be your best gauge in this for seg height measure but again if the patient complains about int and near being too low, raise the seg and switch to short corridor.

[CCGREEN]

How do you determine the true POW during fitting, i.e. the position at which the lens will come to rest after nasal geometry, perspiration, body oils, and motion dislodge it from where it was first set on the face? Are there any tricks to determine this natural POW? I'm not talking about sports or other extremes, but the difference between where a patient will initially put on his frame, and the place where a frame will naturally want to come to rest. I've found they're not necessarily the same.

A patient with OD -2.75 -3.00 002 OS -2.5 -2.75 180 add +2.25 chose a snug fitting 46-24-150 retro frame and was fitted with Shamir Auto II fixed 18mm in 1.60 material. On delivery he loved them but returned the next day claiming the reading power (and intermediate, it seems) was "too low". On a hunch I asked him to spend an hour doing ordinary activities with his glasses on before coming to see me again. I told him not to re-adjust the frame position unless necessary for safety. When he came in, I measured and marked the OC. I then asked him to take his glasses off and put them back on in the same position as earlier in the day. I measured OC again. There was a full 3mm difference between the two OC positions, more than enough to be very significant in his rx.

With that kind of movement that we have very little control over is exactly why I am not really sold on all the new fangled improved ways of making glasses that are supposed to help you see soooooo much better then the old fashion grind method. "Oh but we can the the power to within 1/8 diopter. Can the most of the patients out there even pick up on such a suttle diffrence? I think not. " And if you use this type progressive you will increase their field of view by a 1/3 and colors will be much more crisp and sight will be super awesome."
All of this and you can charge another $300. for a pair of specs that will slip and slide and therefore everything you were trying to accomplish just went out the window.
And really now, how many patients do you work with that can really really perceive the difference or even know the difference in between digital processing and grinding, do they even care?
Not trying to sound negative here. Just trying to be realistic and help keep things in perspective.

[rdcoach5]

With that kind of movement that we have very little control over is exactly why I am not really sold on all the new fangled improved ways of making glasses that are supposed to help you see soooooo much better then the old fashion grind method. "Oh but we can the the power to within 1/8 diopter. Can the most of the patients out there even pick up on such a suttle diffrence? I think not. " And if you use this type progressive you will increase their field of view by a 1/3 and colors will be much more crisp and sight will be super awesome."
All of this and you can charge another $300. for a pair of specs that will slip and slide and therefore everything you were trying to accomplish just went out the window.
And really now, how many patients do you work with that can really really perceive the difference or even know the difference in between digital processing and grinding, do they even care?
Not trying to sound negative here. Just trying to be realistic and help keep things in perspective.

You are confusing Lerral's issue with Position Of Wear which I described above as really patient's posture. POW takes into consideration the pantoscopic angle that the eye makes relative to the concave surface and doesn't change with posture. Digital grinding is an altogether different topic and IMHO makes a world of difference in sharpness in lenses. We use an IOT designed progressive that almost always gets a " WOW ! " response that everything is so clear. If you are not offering such a lens, you are generations of technology behind. The cost is only slighty more than the older designs. PM me if you want prices.

[Optoanomaly]

Hmm, Not really familiar with shamir product due to unavailability of the product in my country however 18mm PV is what you fit, correct? Check again, you might have put a regular corridor progressive in that frame. It's impossible for regular corridor to have a wide intermediate and reading if they are being fit with 18mm segment height.

3mm difference in OC position is easily corrected by adjusting the end-temple, I dont think that's the main problem though

[Barry Santini]

I think there is a continued tendency to look toward the longest corridor as providing the best overall lens performance. A Shamir 18mm corridor, i understand, equates to a 20mm fitting height. If true, then the eye depression angle would be close to 40 degrees at a normal VD of 13.5mm. This is 10 degrees more than what we now know is the common/comfortable eye depression angle of 30 degrees. Try refitting with a revised pupil height and a 15mm corridor for superior comfort and utility.

B

[drk]

Barry:
Can you help me find some of those good references, for me to read and learn?

Where did you read about the 30 degrees?

Also, is there a source for what the corridor lengths are on various designs (not manu's rec'd fitting height).

Much appreciated!

[Robert Martellaro]

So, how do you determine a patient's natural position of wear, i.e. the place on the nose where a given frame is more or less stable?

I push down on the top of the bridge, rock it slightly, observe as we chat, and call that the "final resting place". For folks who like to push their eyeglasses up unrealistically high, I tell them it's not going to happen, that I can't make them stay there, no way no how.

I think there is a continued tendency to look toward the longest corridor as providing the best overall lens performance.

I think that's a no brainer, especially for the higher adds, although avid readers might prefer a slightly more aggresive power rate.

A Shamir 18mm corridor, i understand, equates to a 20mm fitting height. If true, then the eye depression angle would be close to 40 degrees at a normal VD of 13.5mm. This is 10 degrees more than what we now know is the common/comfortable eye depression angle of 30 degrees.

I see it somewhat differently, knowing that 100% of the add for the Auto 18 is at 13mm. I suspect that one would be sampling the full power if the reading depth is 15.5mm. Compare this with the Physio (and the 'S' it seems) where the add is only 85% at 12.4mm.

is there a source for what the corridor lengths are on various designs (not manu's rec'd fitting height).

As far as I know, only from the manufacturer, or a lens mapper. Keep in mind that the corridor length can be defined in different ways- sometimes as the distance from the DRP to 85% of the add, or to 100% of the add. But, the corridor length might also vary by fitting height, or by distance power. If you want to know for sure, wear it, preferably at sufficient height to eliminate software manipulation, if applicable (20mm should be sufficient).

[drk]

Dang, that's complicated.

[Robert Martellaro]

Dang, that's complicated.

Not so much. Make a couple pair with a different PAL design in the same frame, then kick back in your easy chair with your newspaper, turn down the lights a notch or two, and you'll find out soon enough which lens has the best near function!