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Medical Forum / General / Vision / October 2007Advice, vdu glasses from reading prescription
I'm hoping for some advice to help me order a pair of specs for computer use from an online store. I've got a recent prescription for reading glasses that are great for focusing at around 35cm, but not very suitable for computer work: R -0.25/0.50X160 L +0.50/0.50X180 Add Near +1.75 My script doesn't give a figure for 'inter', and as I want to make the order as fool proof as possible, I was going to order reading specs and adjust the 'add +1.75' to a lower power to make them suitable for use at around 100cm distance. Is there a rule of thumb I can apply to get the correct 'add' figure from what I've already got?. Hope my question makes sense. I'm 53 yrs, if it matters! Something's wrong. If you're 53, it's inconsistent that a +175 add should be clear at 35 cm. Not impossible, just off from what we'd expect. Normally it takes about +2.75 to get clear vision at 35 cm. If you've actually measured it, I'd ask you to re-measure and determine the _range_ rather than the midpoint. I'm guessing you mean you can see _up to_ 35 cm away. How far out can you push that same target before it starts to blur? 40 cm? 50? -MT > Something's wrong. If you're 53, it's inconsistent that a +175 add should be > clear at 35 cm. [quoted text clipped - 9 lines] > > -MT Thank you for your reply....Yes you are right! I didn't measure it before, I was repeating what I thought the optician said and I must have made a mistake, sorry. OK Ive measured the range of clear focus and it's 44cm to 65cm when viewing my LCD screen, and curiously different at 34cm to 74cm when viewing the printed page. Is that normal? I should just add that these distances are measured with my current reading glasses with an add of +1.50. When I had an eye test 2 months ago the difference from my previous prescriptions was too small to warrant a new pair of specs. that's why I'm still using specs with a +1.50, I've had these specs for 5 years now bye the way (my first pair of reading glasses), and in all that time not enough change to warrant a new pair. My optician has told me I still have pretty good vision for my age. Any advice appreciated. > OK Ive measured the range of clear focus and it's 44cm to 65cm when > viewing > my LCD screen, and curiously different at 34cm to 74cm when viewing the > printed page. Is that normal? It is what it is. It's noteworthy that the midpoint of both measurements is about 54 cm. Well, nominally if you want clear vision at 100 cm, you'd want a 1.00 diopter add. Those glasses wouldn't be so hot for printed work, making it difficult to see your bank statement while reconciling checks on the screen. Since you're talking about online prices, I'd recommend a progressive to cover a more useful range: R +0.50-0.50x160 L +1.25-0.25x180 add +1.00 The "tops" would be clear out to 133 cm (+075 effective add), and the bottom clear up to about 40 cm (+1.75 add). The cheapest progressives work pretty well with low add powers like +1.00. -MT, OD > Since you're talking about online prices, I'd recommend a progressive to > cover a more useful range: [quoted text clipped - 8 lines] > > -MT, OD Thank you for the advice, progressive sounds like a good idea. Just one clarification first please, on my prescription the CYL is +50 for both eyes, on the version you give above, have you adjusted this to -0.50 and -0.25, or is simply the shorthand way it's written? As you can tell I don't fully understand the prescription and the way that SPH and CYL appear to be able to be manipulated to end up with the same type of correction. Much appreciated. > Thank you for the advice, progressive sounds like a good idea. Just one > clarification first please, on my prescription the CYL is +50 for both > eyes, on the version you give above, have you adjusted this to -0.50 and > -0.25, or is simply the shorthand way it's written? You're absolutely right, it's crucial and I only assumed minus because that's what I work in. If you look back, you posted the original with a "/" rather than either plus or minus. > As you can tell I don't fully understand the prescription and the way that > SPH and CYL appear to be able to be manipulated to end up with the same > type of correction. It's a guild secret, designed to confuse the laity. Can you find the pentagram? :) Yours should read R +050+050x160. -MT > Yours should read R +050+050x160. > > -MT OK thank you for your patience, before I place an order I need to be sure I'm not making any wrong assumptions. As always a little knowledge equals danger. So should a progressive prescription look like this. R +050+050x160 L +125+025x180 add +1.00 or like this R +050+050x160 L +125+050x180 add +1.00 I can't see why the CYL for L became +025 from +050 on the original, if it's just part of the magic I'll accept that it should be. Sorry to have to ask again for clarification and I do appreciate your help. > R +050+050x160 > L +125+050x180 > add +1.00 > > I can't see why the CYL for L became +025 from +050 on the original, if > it's just part of the magic I'll accept that it should be It's what I get for typing before coffee - the cyl value should *not* change. That was my typo. > Sorry to have > to ask again for clarification and I do appreciate your help. Sure. Since you want clarity, I have to ask about the PD. The distance between your pupils has to be specified with the order. PD changes with working distance (you "converge") and PAL orders usually specify it in detail. Details like seg height and monocular PD are not as critical with your low prescription, and a decent pair could be made with just a "distance PD." -MT >> R +050+050x160 >> L +125+050x180 >> add +1.00 That's great, thank you so much. > Sure. Since you want clarity, I have to ask about the PD. The distance > between your pupils has to be specified with the order. [quoted text clipped - 5 lines] > > -MT With the help of Mrs Edward I've got a PD measurement of 66mm. I did read that with a mild prescription it's not so critical, though more so with progressives than single distance. I think 66 is reasonably accurate, whilst I'm focusing in the distance. I'm ready to order that well needed pair of specs which will stop either trying to read the screen without any, or having to get too close with them on. Thanks again for your patience and advice, much appreciated. > As you can tell I don't fully understand the prescription and the way that > SPH and CYL appear to be able to be manipulated to end up with the same > type of correction. More seriously, it's just two ways of describing a football-shaped surface. Imagine a football. Imagine measuring the curvature along the seams (long axis) as say, 40 units of curvature. Along the short axis, across the seams, say it measures 60 units, so the difference between steepest and flattest is 20 units. You can describe the surface as 40 + 20 or 60 - 20 and you get the same shape. The "a+b" form always starts with the flatter surface and the "c-b" form always starts with the steepest. To convert from one to the other, you must also show that the starting point is no longer the 160 meridian, but instead it's 070, 90 degrees away. So, +050+050x160 is equivalent to +100-050x070. -MT > More seriously, it's just two ways of describing a football-shaped surface. > [quoted text clipped - 13 lines] > > -MT A very clear explanation, thank you. I now understand why my first prescription expressed with -ve values, was actually the same as the next one even though the numbers are very differnt. The optician told me they were close enough, but without any explanations, now I get it! > > OK Ive measured the range of clear focus and it's 44cm to 65cm when > > viewing [quoted text clipped - 3 lines] > It is what it is. It's noteworthy that the midpoint of both measurements is > about 54 cm. Well, perhaps not, except to rule out measurement error. The range of clear focus is always heavily dependent on illumination level. It shouldn't matter for LCD work, since that distance should be fixed, unless: > Well, nominally if you want clear vision at 100 cm, you'd want a 1.00 > diopter add. > > Those glasses wouldn't be so hot for printed work, making it difficult to > see your bank statement while reconciling checks on the screen. you try to read and look at the LCD in the same session. >I'm hoping for some advice to help me order a pair of specs for computer >use from an online store. I've got a recent prescription for reading [quoted text clipped - 12 lines] > >I'm 53 yrs, if it matters! I wonder if computer glasses are really necessary. With an accommodative reserve of +.75D (assuming the ADD is for 40cm), you should get reasonably good focus with the glasses off when viewing objects at 100cm. However, if you're in front of a monitor all day, more accuracy and refinement may be necessary, primarily due to the disparity in the right and left eye Rx. In that case, I would have Rx glasses made by an optician, with the Rx from a doctor, or an optician with experience making specialty glasses. Robert Martellaro ~~~~~~~~~~~~~~~~~~ Optician/Owner Roberts Optical Wauwatosa Wi. ~~~~~~~~~~~~~~~~~~ "Science is a way of trying not to fool yourself." - Richard Feynman |
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