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Medical Forum / General / Vision / March 2005Lens recommendations, please
Current info: OD -7.00 +1.00 139 OS -7.50 +1.50 038 ADD +200 Spectralite FT28, 57-19 frames, 45 mm lens height, edges polished, not rolled. I spend a lot of work time at a computer, approx 20 inch sight distance. It's getting difficult to see the screen through either part of my current lenses. I occasionally umpire baseball, so impact resistance is of concern. (Though the mask does its job.) I'm still looking at FT28 vs. progressives, unless someone has a good argument for progressives. Questions: I've seen references to Trivex. Looks similar to Spectralite, but lighter in weight with better impact resistance. Looks like Trivex is an advancement over Spectralite. Which would you recommend? Any 1.6x materials out there worth considering? Abbe value is a big concern. I'm considering frames with with a smaller lens height, maybe half-rimless. Would a mid-index look particularly thick in a half-rimless frame? How much difference would a 1.6x make? Might it make sense to get a second pair with the top set for computer distance, and the bifocal for reading? If so, how does one alter the prescription for computer glasses? Add to the sphere and subtract from the add? Thanks in advance, > Current info: > [quoted text clipped - 34 lines] > > Thanks in advance, Trivex (1.53 index) is really an advancement over polycarbonate (1.59 index) in that it provides similar impact resistance and tensile strength, with much better optics (although not quite as thin). In terms of impact resistance, there are really no other choices that I know of. You will not be able to wear computer glasses while umpiring a baseball game (if you value your life). Yes, computer glasses are made by adding to the sphere and subtracting the same amount from the add. Some brands include Sola Access and Zeiss Gradal RD. Opticians can also make custom computer glasses from any progressive design. >Current info: > [quoted text clipped - 8 lines] >distance. It's getting difficult to see the screen through either part >of my current lenses. It should be clear enough looking through the reading area although your neck and back will not be happy to say the least. Check that distance again-usually it's more like 23" to 28" assuming a desktop monitor. >I occasionally umpire baseball, so impact resistance is of concern. >(Though the mask does its job.) Noted. >I'm still looking at FT28 vs. progressives, unless someone has a good >argument for progressives. Can't say for sure unless you we were eye to eye where I could see your glasses and ask numerous questions. I would lean towards your line of thinking...if it's not broken don't fix it. >Questions: > >I've seen references to Trivex. Looks similar to Spectralite, but >lighter in weight with better impact resistance. Looks like Trivex is >an advancement over Spectralite. Which would you recommend? ST28 Spectralite is aspheric, ST28 Trivex is not, resulting in a slightly thinner lens. Some of the weight advantage is lost because of this, but the amount is minor, as opposed to polycarbonate which would be about the same weight as Trivex because of the decrease in thickness. So why use Trivex? It's equal to Poly in impact resistance and in higher lens powers, increased optical performance. If you need a lens with substantial impact resistance, use Trivex. If not, stay with Spectralite. >Any 1.6x materials out there worth considering? Abbe value is a big >concern. Most, if not all ST28s in 1.60 index use an older material with slightly poorer optical performance and have a higher specific gravity, which means a heavier lens. No reason to go there. >I'm considering frames with with a smaller lens height, maybe >half-rimless. Would a mid-index look particularly thick in a >half-rimless frame? How much difference would a 1.6x make? Thicker looking for sure. I would stay with full metal and cut the size down considerably. There is no reason to wear a lens with dimensions that measures 57mm x 45mm. 54mm x 38mm is as large as I would use, even if you had a very wide face. If you feel comfortable, field of vision wise, with a smaller frame then go smaller still. The lens thickness and weight will be reduced substantially by doing so, but don't go smaller than 52 x 34. One exception, if you have adapted to an unusually low bifocal height you might need a deeper vertical measurement to keep its relative position to the eye the same. Make sure the bridge is wide enough so that the lenses sit close to the eyes, with the center of the lens about 5mm below the pupil. This is done by increasing the distance between the nose pads, but the lens thickness may easily interfere with the pads and force a narrower adjustment than was intended. This would place the lens too high and far from the eyes, with the result being a bifocal that is too high and/or narrow, along with substantially reduced field of vision. >Might it make sense to get a second pair with the top set for computer >distance, and the bifocal for reading? If so, how does one alter the >prescription for computer glasses? Add to the sphere and subtract from >the add? That's how I would do it, if the distance to the screen is at least 22". If 20" or less then single vision reading glasses would work fine. You'll probably want about +1.50 to +1.75 added to the distance Rx. Check with your doctor to make sure that the prescribed +2.00 add power is referenced to 40cm or about 16". They will write the proper Rx to match the distance you measured to the screen. >Thanks in advance, Your welcome. Don't forget to use coated optics (anti-reflection) for the best optical performance. Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "If a million people believe a foolish thing, it is still a foolish thing." - Anatole France One more question. Would a PAL help with the computer without having to have a separate pair of glasses? >One more question. Would a PAL help with the computer without having >to have a separate pair of glasses? You will still have to tip your head back to see the monitor clearly, with extremely narrow field of vision both vertically and horizontally. You can get a basic pair of ST28 computer glass for less than the increased fee for the PALs, less still if they are single vision. The inconvenience of having two pair of glasses is not as brutal as eye fatigue and a sore neck and back. The only other option is to increase the distance from the screen to your eyes. This will decrease the blur, at the same time decreasing the object size making small text harder to see. That might require a larger screen and/or decreased resolution. It's usually better to match the optics to the workplace and not the other way around. Hope this helps Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "If a million people believe a foolish thing, it is still a foolish thing." - Anatole France > The only other option is to increase the distance from the screen to your > eyes. I write a lot of "computer" PALs with +050 excess plus in the distance lenses, but subtracted from the add. These are a little blurry when driving, but _heaven_ in the office. It's the best "second pair" for many who work in close environments. +150 adds are always wider than +200. -MT >> The only other option is to increase the distance from the screen to your >> eyes. [quoted text clipped - 8 lines] > >-MT Mike, That's more of a compromise than I would be comfortable with. My monitor at work is a little further away than average at 27", and I need all of +1.25 added to the distance, about -4.25 presently, for the clearest vision. I can recognize people coming in the door but I wouldn't drive with these glasses because I have my regular glasses that provide excellent distance vision. Folks with closer set monitors at 23" or so will need +1.50 of a +2.25 add over the distance Rx. The add for reading in this case would be +.75. The lenses will feel like SV to be sure. I tried one of the "computer lenses" recently. The lab used the companies charts to determine the correct degression. The screen was blurry without -.50 over. I think I'll stick to regular multifocals for computer glasses since I get it right about 98% of the time by doing it this way, as opposed to a lens that no one seems to know where the focus will be. Regards Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "If a million people believe a foolish thing, it is still a foolish thing." - Anatole France Well, this is what I ended up with: OD -6.00 OS -5.50 ADD +200 (This is using the other prescription convention. So my left eye is a little less nearsighted than before Right eye is the same. I don't remember the cylinder - -1.00/-1.50 sounds familiar.) I just ordered a set of Trivex bifocals.. 54 mm lenses (don't remember the height) I'm now thinking about ordering a pair for computer use. One suggestion would be to go with single-vision lenses with: OD -5.00 OS -4.50 The thought is that I could still read, though I'd have to hold the page out a little farther than normal reading distance. Does this make sense? What would the reading distance be with these? I assume distance might be fairly fuzzy. Thanks again. (BTW, the folks at the show said that working Trivex is difficult because of the smell. Now, I'm not going to notice that, but I did find it interesting.) >Well, this is what I ended up with: > [quoted text clipped - 13 lines] >OD -5.00 >OS -4.50 Not if the work distance is 20" as you stated, and if the +2.00 add is for 16", the most common distance that doctors use to Rx the near point. +1.50 would be more like it, or Rt -4.50 and Lt -4.00. Best way to confirm this is to use a trial frame, or hand held lenses over the glasses. Your doctor ( or some experienced opticians) will be able to do this. Just make sure you measure the work distance(s) accurately. >The thought is that I could still read, though I'd have to hold the >page out a little farther than normal reading distance. Does this make >sense? What would the reading distance be with these? Using only half of the add would at about 32". Depth of field will probably be about 5" on either side of 32". See Above. > I assume distance might be fairly fuzzy. Right. The closer you set the focus the more blur you will experience, but not as blurred as one might expect, especially for myopes. Either way don't wear them for driving. >Thanks again. > >(BTW, the folks at the show said that working Trivex is difficult >because of the smell. Now, I'm not going to notice that, but I did >find it interesting.) Regards Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "If a million people believe a foolish thing, it is still a foolish thing." - Anatole France Work distance is actually 24-26". The 2.00 add is for 16". >Work distance is actually 24-26". The 2.00 add is for 16". In that case I would use a multifocal with the add split 50/50 or 60/40, probably the latter. The Rx in your Original post... OD -7.00 +1.00 139 OS -7.50 +1.50 038 ADD +200 would become -5.75 +1.00 x 139 -6.25 +1.50 x 38 Add +.75 Hope this helps Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical robopt@execpc.com ~~~~~~~~~~~~~~~~~~ "If a million people believe a foolish thing, it is still a foolish thing." - Anatole France |
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