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Medical Forum / General / Vision / August 2005regular plastic in drill mounts?
I've been having a bit of trouble adjusting to the trivex lenses in my drill mount frames and the office said they can have the lab put regular plastic lenes in these. Some labs won't do it and others will do it but with a shorter warranty period. I've always heard you HAD to use high index, stronger lenses with drill mounts due to splitting or splintering. Any thoughts? So far I'm a bit hesitant but I do notice the difference in optics vs. my normal lenses. Most labs won't do it because the plastic WILL break at the drill points unless you are fanatically careful with them. I'm concerned about your problems with Trivex, which I dearly love. Was there an Rx change? I'd suspect a difference in Rx before I'd suspect Trivex being at fault, unless you just got a bad lens. What kind are they (single vision, bifocal or progressive)? If progressive, what brands old and new? w.stacy, o.d. >I've been having a bit of trouble adjusting to the trivex lenses in my >drill mount frames and the office said they can have the lab put [quoted text clipped - 5 lines] > > > Most labs won't do it because the plastic WILL break at the drill points > unless you are fanatically careful with them. [quoted text clipped - 6 lines] > > w.stacy, o.d. The prescription is the same between the plastic and trivex lenses. I have astigmatism so that enters into the equation. They checked the glasses with my current ones and there was no difference but stated that some patients are sensitive to the higher index lenses. I did notice that things seemed shorter...or that the ground came up a bit vs. my plastic lenses. This is the third set of lenses in these frames as with the first ones the OC was wrong. The second had basically no base curve and these seem to have more of a bc than my plastic lenses. They're much better and I think I can get used to them...but my vision is not as accurate with these lenses. You still didn't say if they are SV, Bi or Prog. Also, do the lenses have a very faint greenish tinge when you hold them over a piece of white paper? w.stacy, o.d. > > [quoted text clipped - 24 lines] > > > You still didn't say if they are SV, Bi or Prog. Also, do the lenses > have a very faint greenish tinge when you hold them over a piece of > white paper? > > w.stacy, o.d. They are SV. They have AR which gives a faint green reflection when you hold them just right. OK my reason for asking that was that Trivex lenses actually have a very slight greenish tint to them, in addition to or rather separate from the greenish reflection from the coating. Try the test again, but tilt them so that all reflections are directed away from your eyes. If they are really Trivex, you will see a slight green color of the lens itself (you might be able to more readily see this tint by looking straight at the edge. If they are not so tinted, and are "dead white" you didn't get Trivex, you probably got polycarb... w.stacy, o.d. >>You still didn't say if they are SV, Bi or Prog. Also, do the lenses >>have a very faint greenish tinge when you hold them over a piece of [quoted text clipped - 4 lines] > They are SV. They have AR which gives a faint green reflection when you > hold them just right. Hmmm, there is a slight tint but I don't think I would call it green. Maybe more of a very, very slight gray or brown...very slight. The edges are polished and I can't pick up any hint of green when looking at them. Is there any other way to distinguish trivex from poly? Since I clearly paid for trivex from my fee slip, I'd be very disappointed if it was instead poly, especially since I've lamented to the opticians that I don't care for poly due to the reduced optics. The other thing I've found odd (again, maybe not a big deal but...) is that these lenses don't seem much thinner than my regular plastic lenses. Thanks for you help. > Hmmm, there is a slight tint but I don't think I would call it green. > Maybe more of a very, very slight gray or brown...very slight. The [quoted text clipped - 6 lines] > lenses don't seem much thinner than my regular plastic lenses. Thanks > for you help. Trivex (1.53 index) is not much thinner than regular plastic (1.50). Polycarb is 1.59. However Trivex is significantly lighter than regular plastic or polycarb: Regular Plastic (CR-39) 1.32 g/cm3 Polycarb 1.20 g/cm3 Trivex 1.11 g/cm3 What brand of Trivex did you get? Hoya Phoenix or Younger Trilogy? If they are progressives then they will have etchings that identify the lens design and material. The best way is ask to see the lab fabrication order slip itself, which should indicate the lab itself, and what material was ordered. Conceivably, the lab could have "cheated", but that would be rare. Another way, esp. if the lens is fairly strong, is to look at a straight line such as a door frame through the outer periphery of the lens and see how much chromatic aberration you get. If it's poly, you'll see a fair amount of yellow fringes around the straight edge, way more than you'd see with a standard lens or a Trivex. A rather destructive way would be to rub some acetone on the lens. If it damages the lens, it's polycarb. Unfortunately, your SV lenses are not engraved like progressives would be, so there's no easy way. I'm not sure if the Trilogy (Younger) brand of Trivex has the slight green tint to it, but am sure the Phoenix (Hoya) has it, as that's what I use. w.stacy, o.d. > > [quoted text clipped - 25 lines] > > > I did notice that things seemed shorter...or that the ground came up a bit >vs. my plastic lenses. You're a myope? That will go away if you increase the lens tilt (panto). >This is the third set of lenses in these frames as with the first ones >the OC was wrong. The second had basically no base curve and these seem >to have more of a bc than my plastic lenses. They're much better and I >think I can get used to them...but my vision is not as accurate with >these lenses. Does the vision become clearer if you raise the lens? The Trivex lenses are probably aspheric and requires very accurate positioning even with low powers. Check the vertical OCs. There is only one correct base curve. Tell them to use the curve that the lens manufacturer recommends for your Rx. It should be flatter than spherical cr39 if the Trivex is aspheric. >The other thing I've found odd (again, maybe not a big deal but...) is that these >lenses don't seem much thinner than my regular plastic lenses. Thanks >for you help. Depends on how thin they ground the center of the lens. Most of the better labs will make the centers about 1.2mm to 1.0mm, about 1mm thinner than cr39 plastic. Depending on the Rx you can expect an edge thickness reduction from about 40% in low powers to about 15% in higher powers. Hope this helps Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "An expert is a person who has made all the mistakes that can be made in a very narrow field." - Niels Bohr > The Trivex lenses are >probably aspheric and requires very accurate positioning even with low powers. > I'm not sure why you say that. I use a fair amount of Trivex and have not het ordere an aspheric one. I have a bias against aspheric lenses, maybe because of your comment above... >Check the vertical OCs. There is only one correct base curve. Tell them to use >the curve that the lens manufacturer recommends for your Rx. It should be >flatter than spherical cr39 if the Trivex is aspheric. > I also detest the "flatter is better" mantra that seems to be so popular these days. I hate the mirror effect that flat lenses give, and I really don't agree that they "look better". I agree that there is a theoretical "best" base curve for every Rx, but this can be and is often changed for a variety of reasons (maybe not with aspherics (??), but then, as I said, I never use aspherics unless there is no other choice). w.stacy, o.d. >> The Trivex lenses are >>probably aspheric and requires very accurate positioning even with low powers. [quoted text clipped - 3 lines] >not het ordere an aspheric one. I have a bias against aspheric lenses, >maybe because of your comment above... I've had very few problems with aspherics, certainly less than 1% remakes, but sometimes it's better to use the K.I.S.S. principle and keep the headaches to a minimum, especially if you can't have complete control over the dispensing process. >>Check the vertical OCs. There is only one correct base curve. Tell them to use >>the curve that the lens manufacturer recommends for your Rx. It should be [quoted text clipped - 4 lines] >these days. I hate the mirror effect that flat lenses give, and I >really don't agree that they "look better". I know what you mean, although coated optics do soften the appearance significantly. I think the appearance of aspheric moderate to high plus powers lenses is much improved compared to spherical designs, with notable reductions in weight and thickness to boot. >I agree that there is a >theoretical "best" base curve for every Rx, but this can be and is often >changed for a variety of reasons (maybe not with aspherics (??), but >then, as I said, I never use aspherics unless there is no other choice). > >w.stacy, o.d. Using non-best form BCs will introduce power errors and cylinder with eccentric gaze. Not to much of a concern with low powers and single vision lenses, more of a concern with multifocals where the reading depth is at least 10mm, and typically 15mm to 20mm off axis with PALs. Regards, Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "An expert is a person who has made all the mistakes that can be made in a very narrow field." - Niels Bohr
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