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  #1  
Old 09-27-2005, 01:41 PM
Kelly
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Default help with frame sizing and rimless/drillmount questions

I have never worn glasses before and am having some trouble adapting.

I found the following quote:
"The rule of thumb is that the total width of the frame front all the way across, including the endpieces, should be close to the thickness of your head. This will allow for the optimum proportion of the frame to the head, and for the best comfort."

(1.) Does this just imply the width across front of the forehead?
(2.) Does this rule of thumb seem like a good guide?

I'm 6' with a round face, so it is recommended I get narrow/rectangular glasses and more round ones do look kindof silly on me.

My optician has a "replace one time" (60 day) policy if I decide to switch frames and the deadline is fast approaching. I currently have Ralph Lauren 1473, which is brown and has the measurement markings 50/18/130. (It also says 5/2 on the bridge?) Subjectively, I am told by multiple people that they look good on me and do not look too small.

Right/left field of vision is ~30-45 degrees and the up/down is ~20-30 degrees. When looking straight ahead, vision is fine but I see an outline of the frame that reminds me of looking through binoculars. At night, the back of the frame catches lights is more distracting.

My posture and ergonomics aside, if I presently tilt my head to center the bottom center of my 19" monitor as I type this then glance up, I can see the top 1/3rd of my monitor above the top edge of the glasses. I've tried to wear the glasses often, but the height of the vision correction makes dining while talking to someone so weird that I always want to take them off when eating.

From the sides, I feel like my peripheral vision is very restricted. The frames are adjusted so that they flare out slightly and the arms do
not put too much pressure on my temples.

(3.) Should I expect to adapt further? Is 45 days just not enough time to tell?

(4.) Not many people seem to make larger frames but Silhouette does. One of their frames goes as wide as 57 on one vender site with the model "Titan Minimal Art". Is there any disadvantage if I just went with the largest?

(5.) With "rimless" Silhouette, would I notice the "edge" less or more? In other words, is the edge of the lens itself just as distracting as a frame?

(6.) I'm having trouble finding height measurements for these on the web. Is there a good resource?

(7.) For a given model, does lens height increase as you move to wider frames?

(8.) With drillmount designs, would I be able to adjust the tilt just as much as with a normal frame or not at all?

(9.) Some web sites say they require polycarbonate, which I understand has more visual distortions. Other sites say polycarbonate or high index but not standard plastic due to cracking. Are high index just as good in rimless/drillmount?

(10.) If I would not be able to use standard plastic, what is the most distortion-free high index that I could use with a drillmount? (My prescription is not very strong so weight is less an issue but I am easily bothered by visual distortions.)

(11.) With Silhouette specifically, I am looking at models 7508 and 7510 (links below). Would this be a good choice for me?
http://www.silhouette.com/en/product...index.asp?id=6
http://www.silhouette.com/en/product...index.asp?id=8

(12.) Finally, should I just stick with the ones I have now?



Thanks a lot. Partial answers welcomed. :)
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  #2  
Old 09-27-2005, 01:41 PM
William Stacy
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Default

Quote:
I have never worn glasses before and am having some trouble adapting.

I found the following quote:
"The rule of thumb is that the total width of the frame front all the way across, including the endpieces, should be close to the thickness of your head. This will allow for the optimum proportion of the frame to the head, and for the best comfort."

(1.) Does this just imply the width across front of the forehead?
The widest part of the head, which could be anywhere, depending on the shape of the head, but usually is about at the ears.

Quote:
(2.) Does this rule of thumb seem like a good guide?
All other things being unknown or not important, yes. The actual Rx will bend this rule often.

Quote:
I'm 6' with a round face, so it is recommended I get narrow/rectangular glasses and more round ones do look kind of silly on me.

My optician has a "replace one time" (60 day) policy if I decide to switch frames and the deadline is fast approaching. I currently have Ralph Lauren 1473, which is brown and has the measurement markings 50/18/130. (It also says 5/2 on the bridge?) Subjectively, I am told by multiple people that they look good on me and do not look too small.

Right/left field of vision is ~30-45 degrees and the up/down is ~20-30 degrees. When looking straight ahead, vision is fine but I see an outline of the frame that reminds me of looking through binoculars. At night, the back of the frame catches lights is more distracting.

My posture and ergonomics aside, if I presently tilt my head to center the bottom center of my 19" monitor as I type this then glance up, I can see the top 1/3rd of my monitor above the top edge of the glasses. I've tried to wear the glasses often, but the height of the vision correction makes dining while talking to someone so weird that I always want to take them off when eating.

From the sides, I feel like my peripheral vision is very restricted.

The frames are adjusted so that they flare out slightly and the arms do not put too much pressure on my temples.

(3.) Should I expect to adapt further? Is 45 days just not enough time
to tell?
45 days is more than enough. I'd never ask a person to "adapt" for more than 1 week.

Quote:
(4.) Not many people seem to make larger frames but Silhouette does. One of their frames goes as wide as 57 on one vender site with the model "Titan Minimal Art". Is there any disadvantage if I just went with the largest?
Depends on your Rx and your P.D. You should post those.

Quote:
(5.) With "rimless" Silhouette, would I notice the "edge" less or more? In other words, is the edge of the lens itself just as distracting as
a frame?
Yes, esp. if they are polished edges, they will really sparkle.

Quote:
(6.) I'm having trouble finding height measurements for these on the web. Is there a good resource?
Now there's a hint about your Rx. Not enough info, tho'.

Quote:
(7.) For a given model, does lens height increase as you move to wider frames?
Yes, and by the same amount.

Quote:
(8.) With drillmount designs, would I be able to adjust the tilt just as much as with a normal frame or not at all?
You might, but it would be better to let an expert do it.

Quote:
(9.) Some web sites say they require polycarbonate, which I understand has more visual distortions. Other sites say polycarbonate or high index but not standard plastic due to cracking. Are high index just as good in rimless/drillmount?
I would never order polycarb, which are outmoded and trashy. If rimless, get Trivex.

Quote:
(10.) If I would not be able to use standard plastic, what is the most distortion-free high index that I could use with a drillmount? (My
prescriptions not very strong so weight is less an issue but I am easily bothered by visual distortions.)
There are none in existence. Again, get Trivex.

Quote:
(11.) With Silhouette specifically, I am looking at models 7508 and 7510 (links below). Would this be a good choice for me?
http://www.silhouette.com/en/product...index.asp?id=6
http://www.silhouette.com/en/product...index.asp?id=8
Need the P.D. and Rx.

Quote:
(12.) Finally, should I just stick with the ones I have now?
No. If you're not happy, get a remake in Trivex, as big as you want.
w.stacy, o.d.
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  #3  
Old 09-27-2005, 07:32 PM
Mike Tyner
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Default

Quote:
Right/left field of vision is ~30-45 degrees and the up/down is ~20-30 degrees. When looking straight ahead, vision is fine but I see an

(12.) Finally, should I just stick with the ones I have now?
Those angles seem pretty small. Your glasses may be adjusted to sit too far from your eye. Often it's the nosepads that are adjusted to make them sit closer.

When glasses fit closer, they cover larger visual angles and create less distortion.

-MT
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  #4  
Old 09-28-2005, 01:41 PM
Kelly
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Default

Thank you very much for the reply. My responses are below.

Quote:
45 days is more than enough. I'd never ask a person to "adapt" for more than 1 week.
You wouldn't even if the person had never worn glasses?

One odd thing about my perscription is that I had a strange distortion in which things that should have been square or rectangular looked slightly trapezoidal. I'm told this is due to differences in power and it seems that I've adjusted to that ok. As you may expect, when I take the glasses off I now notice the trapezoid in the opposite direction. (In other words, with glasses I at first saw edges on the left of my monitor as taller than the right side. Now that I've adapted somewhat, it looks close to normal with the glasses on. However if I take them off, the right side of the monitor now seems taller than the left side.) No one seemed to have heard it described that way from any of their patients at either clinic or store.

I also have had some difficulty telling when it is the reflectiveness of the frame that bothers me, that it's small enough to always somewhat be in my vision on all sides or if it's the slight (normal) distortion toward the edge of the lenses. These are high-index 1.57 and they're definitely better than the polycarbonates I had tried from another place. They also have the "anti-glare" option.

Some background: I had originally gone to a buy-one-get-one-free place but got discouraged when they didn't get the PD correct AND didn't catch it when I had them check it. After, I went to a reputable opthamologist who really seemed to know his stuff and he had an awesome team. When he sent me to his glasses shop down the street, he never works there of course and I only talk to the optomitrists. They are experienced with normal people but they don't inspire confidence with the unusual cases as I seem to be in almost every regard.

Quote:
(4.) Not many people seem to make larger frames but Silhouette does. One of their frames goes as wide as 57 on one vendor site with the model "Titan Minimal Art". Is there any disadvantage if I just went with the largest?

Depends on your Rx and your P.D. You should post those.
Sorry. I did not have it on me yesterday and was getting nervous about the mentioned deadline so I hoped my questions were general enough to not require it. Here are the numbers:
OD: -1.50 +1.25 X 160
OS: -1.25 +1.00 X 50
PD = 69.5
* The base curve is not provided, please use the base curve from the previous pair of glasses. If this is a new prescription, please use the optical laboratory's recommended base curve.

They measured the PD with the Empire Strikes Back binoculars looking thing so it should be more accurate than the guess and dot with a marker method that the buy-1-get-1-free place did. I made them photocopy my prescription and wrote down the PD after they measured it. Seemed like I was breaking protocol there. :)

So light perscription, lots of astigmatism, right? What does that mean for me for frames?

With the assistance of a compliant coworker, our best estimate of my head size temple to temple (flat, not bent) is between 6 and 6.25in (152.4-158.75mm). My current glasses are 50/18 which would mean 118mm across, right? That's a difference of ~1.5". If I measure the where the arm is extended to where the lens begins, this seems close enough to .75" per side. Does that all sound right to you? I have a very round face but my lineage is German and Native American, so my head isn't as huge as giant basketball players or anything.

If I'm on the right track, do you have any idea how to estimate what the height would be of those Silhouette lenses so I could estimate how much more vertical I might get from them? Sorry if this seems obsessive but the larger model would be a special order and I only get one shot at it. (And they will probably already be annoyed with me.)

Quote:
(5.) With "rimless" Silhouette, would I notice the "edge" less or more? In other words, is the edge of the lens itself just as distracting as a frame?

Yes, esp. if they are polished edges, they will really sparkle.
I was tempted to see what I could do with a marks-a-lot. :)

Quote:
(6.) I'm having trouble finding height measurements for these on the web. Is there a good resource?

Now there's a hint about your Rx. Not enough info, tho'.
I may not have worded that question very clearly. I meant to say that I could not find the height measurements for different Silhoette frames on their web site or on other vendors' sites.

Quote:
(7.) For a given model, does lens height increase as you move to wider frames?

Yes, and by the same amount.
Ok, that's a start. It'd be nice to be able to keep the "aspect ratio" so I got a rectangular look for my round face but still got more lens height.

Quote:
(8.) With drillmount designs, would I be able to adjust the tilt just as much as with a normal frame or not at all?

You might, but it would be better to let an expert do it.
I meant to ask if the drillmount designs could be tilted (by anyone). I would definitely let them do it, but since the tilt helped some with this pair I expect I'll want that ability.

Quote:
(9.) Some web sites say they require polycarbonate, which I understand has more visual distortions. Other sites say polycarbonate or high index but not standard plastic due to cracking. Are high index just as good in rimless/drillmount?

I would never order polycarb, which are outmoded and trashy. If rimless, get Trivex.
I can't remember the brands. Which index number is Trivex? I'm so picky I'd probably get glass if they let me. (I had some awesome Maui Jim polarized sunglasses.... very wide and tall too. Crystal clear.)

Quote:
(10.) If I would not be able to use standard plastic, what is the most distortion-free high index that I could use with a drillmount? (My perscription is not very strong so weight is less an issue but I am easily bothered by visual distortions.)

There are none in existence. Again, get Trivex.
I'm sorry if I'm using the terms incorrectly. My understanding was that there was polycarbonate (worst for distortion), plastic (least distortion) and varying degrees of high-index that are similar to plastic but more durable and can be made thinner. Can you fill in the gap?

Quote:
(11.) With Silhouette specifically, I am looking at models 7508 and 7510 (links below). Would this be a good choice for me?
http://www.silhouette.com/en/product...index.asp?id=6
http://www.silhouette.com/en/product...index.asp?id=8

Need the P.D. and Rx.
Ok. How about now? :)

Quote:
(12.) Finally, should I just stick with the ones I have now?

No. If you're not happy, get a remake in Trivex, as big as you want.
I know I'm a little anxious about new things and this is a bigger deal for me than it should be. I'm trying to monitor myself and make sure these are genuine issues so that I'm not just being a pest of a customer.

Thank you very much for your help with this.

In response to the other poster's suggestion: the glasses slide only a little from the highest closest position throughout the day and the framing concerns I have still exist even after I have just pushed them to the closest point. It does help a little, of course, if they've had time to get nudged a little but not enough to really make a difference. The nose fit seems right.
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  #5  
Old 09-28-2005, 08:45 PM
William Stacy
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Quote:
Thank you very much for the reply. My responses are below.

45 days is more than enough. I'd never ask a person to "adapt" for more than 1 week.

You wouldn't even if the person had never worn glasses?
Not with full time wear. Maybe occasional wear, the less the longer they might take, but full time wear? 1 week MAX (I'm not in the habit of torturing my patients). Actually, my routine advice is to come back if they're not adapted over the weekend.

Quote:
One odd thing about my prescription is that I had a strange distortion in which things that should have been square or rectangular looked slightly trapezoidal. I'm told this is due to differences in power and it seems that I've adjusted to that ok. As you may expect, when I take the glasses off I now notice the trapezoid in the opposite direction. (In other words, with glasses I at first saw edges on the left of my monitor as taller than the right side. Now that I've adapted somewhat, it looks close to normal with the glasses on. However if I take them off, the right side of the monitor now seems taller than the left side.) No one seemed to have heard it described that way from any of their patients at either clinic or store.
Very common, especially if the astigmatism Rx is slightly off axis, or stronger than necessary. Can be normal, but if bothersome, my modus is to recheck axis and reduce cylinder.

Quote:
I also have had some difficulty telling when it is the reflectiveness of the frame that bothers me, that it's small enough to always somewhat be in my vision on all sides or if it's the slight (normal) distortion toward the edge of the lenses. These are high-index 1.57 and they're definitely better than the polycarbonates I had tried from another place. They also have the "anti-glare" option.
Frame awareness also shouldn't take more than a few days of full time wear to get over. Part time wear, and you may NEVER get over it. Same is true of chromatic aberration.
....
Quote:
Sorry. I did not have it on me yesterday and was getting nervous about the mentioned deadline so I hoped my questions were general enough to not require it. Here are the numbers:
OD: -1.50 +1.25 X 160
OS: -1.25 +1.00 X 50
PD = 69.5
* The base curve is not provided, please use the base curve from the previous pair of glasses. If this is a new perscription, please use the optical laboratory's recommended base curve.

They measured the PD with the Empire Strikes Back binoculars looking thing so it should be more accurate than the guess and dot with a marker method that the buy-1-get-1-free place did. I made them photocopy my prescription and wrote down the PD after they measured it. Seemed like I was breaking protocol there. :)

So light prescription, lots of astigmatism, right? What does that mean for me for frames?
No. Light prescription with light oblique astigmatism. P.D. is really
not a factor if they are single vision.

Quote:
(5.) With "rimless" Silhouette, would I notice the "edge" less or more? In other words, is the edge of the lens itself just as distracting as a frame?

Yes, esp. if they are polished edges, they will really sparkle.

I was tempted to see what I could do with a marks-a-lot. :)
Try it. If you like it, you can have it professionally done if it doesn't come out perfectly.

If you're talking a drilled rimless (no eyewire, just a bridge and temples), you can have them size the lenses to anything you want. You want larger, tell them larger. With your Rx, no problem, but demand Trivex material (IMO). First have an O.D. carefully recheck that astigmatism Rx.

Quote:
(6.) I'm having trouble finding height measurements for these on the web. Is there a good resource?

Now there's a hint about your Rx. Not enough info, tho'.

I may not have worded that question very clearly. I meant to say that I could not find the height measurements for different Silhoette frames on their web site or on other vendors' sites.
I think you're talking about the "B" measurement, the maximal vertical dimension in mm, avail. in the big FRAMES book. Again, if rimless, you can upsize, and every mm additional horizontal ("A") measurement, you'll get a mm vertical as well.
Quote:
Ok, that's a start. It'd be nice to be able to keep the "aspect ratio" so I got a rectangular look for my round face but still got more lens height.
Right.
Quote:
I meant to ask if the drillmount designs could be tilted (by anyone). I would definitely let them do it, but since the tilt helped some with this pair I expect I'll want that ability.
no problem.
Quote:
I can't remember the brands. Which index number is Trivex? I'm so picky I'd probably get glass if they let me. (I had some awesome Maui Jim polarized sunglasses.... very wide and tall too. Crystal clear.)
You can't get glass rimless any more. Trivex is around 1.53 and has great ABBE value.
Quote:
I'm sorry if I'm using the terms incorrectly. My understanding was that there was polycarbonate (worst for distortion), plastic (least distortion) and varying degrees of high-index that are similar to plastic but more durable and can be made thinner. Can you fill in the gap?
Not very well. Just google search on "table of abbe" values or something. The higher the ABBE number, the better, and vice-versa.

Quote:
(11.) With Silhouette specifically, I am looking at models 7508 and 7510 (links below). Would this be a good choice for me?
http://www.silhouette.com/en/product...index.asp?id=6
http://www.silhouette.com/en/product...index.asp?id=8

Need the P.D. and Rx.

Ok. How about now? :)
Maybe someone else will look the frames up for you, preferably someone who has you there personally...

w.stacy, o.d.
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  #6  
Old 09-29-2005, 01:41 PM
William Stacy
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Quote:
Is there a more common word to describe that effect? I'm really surprised that it is very common yet no one seemed to understand what I meant when I described it.
Trapezoid effect is perfect, but not everyone seems to have paid attention in elementary geometry. Shape distortion would be another way, but I like trapezoid better due to the specificity.

Quote:
P.D. is really not a factor if they are single vision.

The opthamologist had emphasized the importance of optical center. Does this mean the same thing? Do you think he was wrong to say this with my prescription?
Usually it is, but if they are single vision, your powers in the meridians that count (180 degree, horizontal), are almost zero, so unless they accidentally grind in some prism, the location of the optical centers is pretty trivial.

Quote:
I remember the optician saying they could do different styles of the Silhoettes in other sizes but that I would not be able to purchase the matching tint clip if it wasn't a size they offered. I didn't realize she must have meant that they could actually make them to any size.
That's true. Your clips would be a loss.
Quote:
If I do get larger frames lenses that give me more peripheral on the left and right outside, my eyes will be closer to the inside edge of the lens than the outside edge of lens. With my prescription, will the distortion resulting from not looking through the center of the lens be noticeable? Am I misunderstanding the manufacturing process? Is *this* the point of the "optical center"?

In your Rx, it's really not a problem, the amount of induced prism being
near zero. The higher the power, the more significant displacement of the optical centers become. Put another way, if you consider a zero power lens, the optical center is not defined; that is, you could "decenter it" all the way to china and it wouldn't induce ANY prism.

Quote:
You can't get glass rimless any more. Trivex is around 1.53 and has great ABBE value.
Just google search on "table of abbe" values or something. The higher the ABBE number, the better, and vice-versa.

I found this chart: http://www.krspecs.com/abbe.html

In that chart, the Sola 1.53 actually has a higher abbe value than Trivex (47 compared with 43). I doubt I will have a choice in this anyway, though. I'm sure they will only offer one brand at a given index value. I will ask, though. If this Sola is available, is there any reason not to take it over the Trivex?
For drill mounts you want the strength of Trivex which is orders of magnitude better in that dept. The abbe difference is not significant.

Quote:
Also, I can't help but notice that the Trivex has a specific gravity of 1.11, which is much lighter than any of the others. How is it that Trivex is thicker than the others but still lighter? ("Space technology?")
Lower specific gravity, and yes, a result of resin research.

Quote:
Am I understanding correctly: *The edge of a drill-mount will be less noticeable than a plastic or metal reflective frame.
Maybe. Since it's flat-beveled and often polished, it can often be MORE noticeable. This can be minimized with a variety of edge treatments.

Quote:
* A drill-mount can be made in any size. The shape of the lens will be the same at any size as both dimensions are increased at the same rate.
True, within reason.

Quote:
* If I measure the width of my head from temple to temple, this number should approximately match: eye size * 2 + bridge.
Not quite. Add in the size of the endpieces, which usually stick out a bit from the outsides of the lenses.

w.stacy, o.d.
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  #7  
Old 09-29-2005, 01:41 PM
Kelly
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Quote:
Adaptation Not with full time wear. Maybe occasional wear, the less the longer they might take, but full time wear? 1 week MAX (I'm not in the habit of torturing my patients). Actually, my routine advice is to come back if they're not adapted over the weekend.
It definitely took a little longer for me to adapt to the "trapezoid." I take them off when eating, sleeping and talking with people face to face but keep them on otherwise. Most of my time is in front of a computer and they are always on then.

Quote:
Trapezoid effect Very common, especially if the astigmatism Rx is slightly off axis, or stronger than necessary. Can be normal, but if bothersome, my modus is to recheck axis and reduce cylinder.
Is there a more common word to describe that effect? I'm really surprised that it is very common yet no one seemed to understand what I meant when I described it.

I originally saw an optometrist next door to a buy-1-get-1-free place. This was the first time I had my vision checked in many years. This was a very quick process and my eyes were not dilated. He wrote the perscription and I went next door to shop for frames. The trapezoidal problem bothered me immediately when I began looking at monitors, paper, or anything else that was normally square or rectangular and close up. I went back to the store to talk to the optician and he made some adjustments that didn't seem to do much, then checked the optical center and said it was fine. I then went back to the optometrist and he spent more time with me. He checked the glasses and immediately said the optical center was off. He then sat with me and constructed some makeshift goggle glasses using an errector set looking collection of lenses in a drawer. This time he found my eyes to be very slightly worse than originally found. However, he said that if I was having trouble adapting that I could still try a slightly weaker prescription. When I looked through the makeshift glasses, however, the trapezoidal effect was just as bad but the letters were not quite as crisp. He wrote this very slightly weaker prescription for me but I was not really content.

On a recommendation, I then saw an opthamologist who had an entire team of really sharp people working in a sort of assembly line. One person would dilate my eyes, another would show me slides. The part the doctor did himself involved shining bright lights into my pupils, which I assume was to look for signs of disease and to talk with me a little about my complaints of dry, itchy eyes which I really did have but bringing it up caused the visit to fall under my insurance coverage. The slides test was more thorough at this place but the prescription was very similar to the stronger prescription that the optometrist had measured on my return visit to him. I tried to explain the trapezoidal effect to my doctor but as I said, no one really seemed to be able to relate to my description. He asked to see my glasses and also found the optical center to be off. He also said the glasses were not nearly large enough for the size and shape of my face.

He then recommended that I visit a "real" optical shop, which he just so happened to own one of. He said, "Even there, you will only find a handful of frames that will be right for your size and shape but they'll be able to help you with that better there." This makes me think that the doctor and his opticians were not really on the same page about sizing. The optician showed me several frames that were mostly 18-20/49-50. As you know, these are fairly common sizes and not really much larger at all than the previous frame that the doctor had condemned. The doctor said it was important to get my pupils near the center of the lens and admittedly, these frames do achieve that more. If I get wider lenses than this for a wider frame, that will be probably be less true.

I believe the prescription is accurate in that this prescription yields the sharpest text/best focus. If it could be off in some other way, I'm not sure what to look for.

Quote:
Frame awareness also shouldn't take more than a few days of full time wear to get over. Part time wear, and you may NEVER get over it. Same is true of chromatic aberration.
This is very contrary to what the opticians at the shop had to say. They said, "Some people never get used to it and always hate wearing glasses." As you can imagine, this was a somewhat frustrating response for me. When I described how I felt, they said that if it was the frames that bothered me they could do the exchange once as long as it was within 60 days as that's what their agreement with the lab is. (I suddenly felt more foolish for going to the doctor's shop when I found out they were outsourcing the lens making anyway.) They said that if it was just peripherally looking through the edge of the lens that some distortion there is normal and that a larger lens would only make that worse.

Quote:
P.D. is really not a factor if they are single vision.
The opthamologist had emphasized the importance of optical center. Does this mean the same thing? Do you think he was wrong to say this with my perscription?

Quote:
If you're talking a drilled rimless (no eyewire, just a bridge and temples), you can have them size the lenses to anything you want. You want larger, tell them larger. With your Rx, no problem, but demand Trivex material (IMO). First have an O.D. carefully recheck that astigmatism Rx.
The Silhouettes I'm looking at are drill-mounted. They only have titanium flexible temples and a bridge.

I remember the optician saying they could do different styles of the Silhoettes in other sizes but that I would not be able to purchase the matching tint clip if it wasn't a size they offered. I didn't realize she must have meant that they could actually make them to any size.

If I do get larger frames lenses that give me more peripheral on the left and right outside, my eyes will be closer to the inside edge of the lens than the outside edge of lens. With my prescription, will the distortion resulting from not looking through the center of the lens be noticeably? Am I misunderstanding the manufacturing process? Is *this* the point of the "optical center"?

Quote:
You can't get glass rimless any more. Trivex is around 1.53 and has great ABBE value. Just google search on "table of abbe" values or
something. The higher the ABBE number, the better, and vice-versa.
I found this chart: http://www.krspecs.com/abbe.html

In that chart, the Sola 1.53 actually has a higher abbe value than Trivex (47 compared with 43). I doubt I will have a choice in this anyway, though. I'm sure they will only offer one brand at a given index value. I will ask, though. If this Sola is available, is there any reason not to take it over the Trivex?

Also, I can't help but notice that the Trivex has a specific gravity of 1.11, which is much lighter than any of the others. How is it that Trivex is thicker than the others but still lighter? ("Space technology?")

I doubt this effects me. My perscription is so light that weight probably isn't a factor and the Sola 1.53 is only slightly heavier at 1.21. It's just curious.

Quote:
Maybe someone else will look the frames up for you, preferably someone who has you there personally...
I have looked at the Silhouettes (and every other frame they carry that is in a somewhat larger size) in the store. What I'm asking here is only the mechanics, not the aesthetics.

Am I understanding correctly:
* The edge of a drill-mount will be less noticeable than a plastic or metal reflective frame.
* A drill-mount can be made in any size. The shape of the lens will be the same at any size as both dimensions are increased at the same rate.
* If I measure the width of my head from temple to temple, this number should approximately match: eye size * 2 + bridge.

Thanks again for your replies. It is very satisfying to begin to understand this. The topic was foreign to me and I'm never content to treat something I'm spending a lot of time and money with as a black box.
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  #8  
Old 09-29-2005, 07:32 PM
Kelly
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Quote:
P.D. is really not a factor if they are single vision.

The opthamologist had emphasized the importance of optical center. Does this mean the same thing? Do you think he was wrong to say this with my prescription?

Usually it is, but if they are single vision, your powers in the meridians that count (180 degree, horizontal), are almost zero, so unless they accidentally grind in some prism, the location of the optical centers is pretty trivial.
The first glasses I had were polycarbonate and there definitely was some prism distortion. Maybe this is why he said it, but he could have as easily suggested another lens material.

Quote:
In your Rx, it's really not a problem, the amount of induced prism being near zero. The higher the power, the more significant displacement of the optical centers become. Put another way, if you consider a zero power lens, the optical center is not defined; that is, you could "decenter it" all the way to china and it wouldn't induce ANY prism.
That makes sense to me--I only thought the high cylindrical and axis numbers might make the optical center more important.

Quote:
Trivex vs Sola 1.53
For drill mounts you want the strength of Trivex which is orders of magnitude better in that dept. The abbe difference is not significant.
I'll hope they can do Trivex, then. If not, is the Sola 1.53 not the best alternative? Next down the list would be Hoya 1.56, which I think may be what I have now in the existing frame.

Quote:
Am I understanding correctly: *The edge of a drill-mount will be less noticeable than a plastic or metal reflective frame.

Maybe. Since it's flat-beveled and often polished, it can often be MORE noticeable. This can be minimized with a variety of edge treatments.
I was afraid of something like that. One web site vendor offered and edge treatment. If the shop I've purchased from doesn't, is this something I can do myself?

Quote:
* If I measure the width of my head from temple to temple, this number should

Not quite. Add in the size of the endpieces, which usually stick out a bit from the outsides of the lenses.
The endpieces are usually adjustable, aren't they? The frame I have now does not put too much pressure on the sides of my head, the ends are just angled outward slightly.

A couple other things I thought to ask: Is there a significant quality difference between brands of AR coating? They had a couple of options there but they didn't offer much opinion on them.

I don't need any other coating for this type of lens, right? (It should already be scratch resistant and UV blocking enough...?)
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  #9  
Old 09-29-2005, 08:36 PM
William Stacy
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Quote:
The first glasses I had were polycarbonate and there definitely was some prism distortion. Maybe this is why he said it, but he could have as easily suggested another lens material.
That was chromatic aberration more than prism distortion, but it is very similar.

Quote:
In your Rx, it's really not a problem, the amount of induced prism being near zero. The higher the power, the more significant displacement of the optical centers become. Put another way, if you consider a zero power lens, the optical center is not defined; that is, you could "decenter it" all the way to china and it wouldn't induce ANY prism.
That makes sense to me--I only thought the high cylindrical and axis numbers might make the optical center more important.
It's a bit complex, but since you're persisting, here it is: the power of the lens varies smoothly from meridian to meridian around the lens,from the sphere power AT the axis of the astigmatism to the algebraic sum of sphere and cylinder powers AT the opposite meridian (90 degrees away from the axis). That's why I say your powers are near zero at the 180 meridians (the horizontal). The closer the power to zero at 180, the less important the OCs become, since prism power equals power (at 180) times the decentration in cm, with the resultant being in prism diopters.

Quote:
I'll hope they can do Trivex, then. If not, is the Sola 1.53 not the best alternative? Next down the list would be Hoya 1.56, which I think may be what I have now in the existing frame.
No problem except for the drilling part. Anything but TRIVEX is prone to breakage at the drill points, (or "starring" in the case of polycarb).
Quote:
The endpieces are usually adjustable, aren't they? The frame I have now does not put too much pressure on the sides of my head, the ends are just angled outward slightly.
Fine
Quote:
A couple other things I thought to ask: Is there a significant quality difference between brands of AR coating? They had a couple of options there but they didn't offer much opinion on them.
Make sure you get the best avail. for the material you choose. In the case of Hoya Trivex, it's Super High Vision AR coat. And make sure it has a redo warranty if it scratches...

Quote:
I don't need any other coating for this type of lens, right? (It should already be scratch resistant and UV blocking enough...?)
Right.

w.stacy, o.d.
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  #10  
Old 09-30-2005, 01:41 AM
Kelly
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Thanks for the explanations. Was the edge treatment on the drill-mounts something I can do myself if it's not something the shop I've purchased from can offer?
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  #11  
Old 09-30-2005, 01:16 PM
William Stacy
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Sure, you can "paint" them, if you're fairly careful. There are special felt tip pens used in the profession for this, but you have to be very careful to do it right, get it uniform, and try to keep it off the polished/molded surfaces. Good luck.

w.stacy, o.d.
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  #12  
Old 09-30-2005, 01:41 PM
Quick
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What about lightly sanding with super fine grit sand paper to dull the surface? I would expect it to be easier to get uniform than "painting" with less chance of a whoopsie into unwanted areas.

-Quick
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  #13  
Old 10-02-2005, 12:19 PM
William Stacy
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Maybe, but why not let the lab do it? Unless you got lots of free time and/or just like to tinker, the price is probably worth it. And if there's a whoopsie, they pay for it. But sanding, sure why not?

w.stacy, o.d.
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  #14  
Old 12-31-2006, 06:51 AM
dmid dmid is offline
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Default Trapezoidal shape distortion - new prescription glasses

--------- Quoted Kelly ----------
One odd thing about my prescription is that I had a strange distortion
in which things that should have been square or rectangular looked
slightly trapezoidal. I'm told this is due to differences in power and
it seems that I've adjusted to that ok. As you may expect, when I take
the glasses off I now notice the trapezoid in the opposite direction.
(In other words, with glasses I at first saw edges on the left of my
monitor as taller than the right side. Now that I've adapted somewhat,
it looks close to normal with the glasses on. However if I take them
off, the right side of the monitor now seems taller than the left
side.) No one seemed to have heard it described that way from any of
their patients at either clinic or store.

--------- Quoted William Stacy ----------
Very common, especially if the astigmatism Rx is slightly off axis, or
stronger than necessary. Can be normal, but if bothersome, my modus is
to recheck axis and reduce cylinder.
-----------

I am curious to hear what you ended up doing to correct the trapezoidal shape distortion. I just got my first pair of glasses and have the exact same problem.

I may have caused this problem myself by being such an uber cheapskate. I ordered my glasses online (for $8.95+$5shipping) but the OS-CYL on the glasses I got is .25 off from my prescription. I have my doubts that that is the cause of my problem though because I'm pretty sure my o.d. said I could really use up to a 3.5 correction but he was giving me a weaker OS-CYL prescription because my brain would have trouble adjusting as a first time glasses wearer. The glasses are great otherwise, super clear, it's just that my monitor is now 15% taller on the left side.

I am positive it's something with the (OS) left eye since when I only use my right eye it looks normal. Anyhow, I would like to get someone's opinion on if I should pay for a recheck or just go ahead and order a new pair to get the correct prescription.

Prescription:
OD-SPH: -.50
OD-CYL: -1.25
OD-AXIS: 90
OD-ADD: 0
OS-SPH: -.50
OS-CYL: -2.25
OS-AXIS: 1
OS-ADD: 0
PD-Pupillary Distance: 64

Glasses:
OD-SPH: -.50
OD-CYL: -1.25
OD-AXIS: 90
OD-ADD: 0
OS-SPH: -.50
OS-CYL: -2.00
OS-AXIS: 1
OS-ADD: 0
PD-Pupillary Distance: 64

Thanks for any help!
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