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Medical Forum / General / Vision / June 2005Bitoric RGPs
Just wondering ...in what circumstances would bitoric RGPs be required? Are they usually difficult to fit? All I know about them right now is that they're going to put a large hole in my wallet. ;) > Just wondering ...in what circumstances would bitoric RGPs be required? > Are they usually difficult to fit? All I know about them right now is > that they're going to put a large hole in my wallet. ;) Only when soft lenses won't work and spherical gas perms also won't work. Usually it's when there is a whole lot of astigmatism and/or the total astigmatism doesn't "match" the corneal toricity. I haven't used a bitoric in several years, mostly because toric soft lenses have gotten pretty good. w.stacy, o.d. Oh, and about the difficulty of fitting, not particularly, since "the lab" does most of the calculations. There's a certain amount of voodoo optics involved, in fact it is the one area of ophthalmic optics I personally had trouble with in college, which is why I always let the lab figure it out, based on K readings & refractive error. If you'll post those 2 items, I can tell you whether bitorics are indicated or not. w.stacy, o.d. > Oh, and about the difficulty of fitting, not particularly, since "the lab" > does most of the calculations. There's a certain amount of voodoo optics > involved They (the lab) give you also advise in fitting, thinking about the two inner radi William? Why should people wanted there lenses fitted by you if your lab decide what the data outcome of the contactlens should be? One nice thing in fitting contactlenses is to be sure why you wanted the contactlens just a bit flatter, steeper, smaller, larger, fronttoric, innertoric, etc ect. Your contactlens-lab can't observe the movement or just the lack of it, they are not capable to check the tearflow between lens and cornea etc. No William, I certainly do not agree with you when your saying ''Oh, and about the difficulty of fitting, not particularly'' For the ''voodoo'' part, I leave that to Otis, he is so familiar with the right use of chickens.  SignatureFree to Marcus Porcius Cato: ''Ceterum censeo Carthaginem esse delendam" In conclusion, I think that the "Otis therapy" should be destroyed Jan (normally Dutch spoken) >>Oh, and about the difficulty of fitting, not particularly, since "the lab" >>does most of the calculations. There's a certain amount of voodoo optics >>involved > > They (the lab) give you also advise in fitting, thinking about the two inner > radi William? Actually, they do offer expert advice on the fitting, and even base curves. They have experts who make hundreds of these lenses a year, while I might not order one in a year or more. Obviously I'm going to give input based on trial lenses that I always evaluate on the eyes first. > Why should people wanted there lenses fitted by you if your lab decide what > the data outcome of the contactlens should be? Because they can't legally go to the lab? Obviously the outcomes are evaluated by me, and the buck stops here. > One nice thing in fitting contactlenses is to be sure why you wanted the > contactlens just a bit flatter, steeper, smaller, larger, fronttoric, > innertoric, etc ect. No argument there. I am the fitter, of course. > Your contactlens-lab can't observe the movement or just the lack of it, they > are not capable to check the tearflow between lens and cornea etc. Same answer. I was obviously referring to the INITIAL LENS SELECTION. > No William, I certainly do not agree with you when your saying ''Oh, and > about the difficulty of fitting, not particularly'' I don't think the fitting is much more difficult than a spherical RGP if you have the help of a lab expert. > For the ''voodoo'' part, I leave that to Otis, he is so familiar with the > right use of chickens. touche' w.stacy, o.d. Thanks for the input so far ... Unfortunately I had a horrible time with soft torics. On many days my vision was no better than about 20/60 or 20/70. It was pretty crazy. I'm not sure what a K reading is, so no luck there. It's also difficult to say what my cylindrical error is. Last year it was about 4.25 R and 2.25 L ... this year it came out to be R 2.75 and L 1.75 however it's not clear whether that was a "real" change or whether it was a temporary change caused by the soft contacts. The first trial lens that he put into my right eye felt absolutely horrible ... like it was "popping" up every time I blinked ... Gee that wasn't of much help, was it? ;) > Oh, and about the difficulty of fitting, not particularly, since "the > lab" does most of the calculations. There's a certain amount of voodoo [quoted text clipped - 6 lines] > > w.stacy, o.d. > Thanks for the input so far ... > > Unfortunately I had a horrible time with soft torics. On many days my > vision was no better than about 20/60 or 20/70. It was pretty crazy. Wow. Sounds like a bad fit. I don't recall a toric soft lens fit that couldn't get close to 20/30 or 20/25. > I'm not sure what a K reading is, so no luck there. It's also > difficult to say what my cylindrical error is. Last year it was about > 4.25 R and 2.25 L ... this year it came out to be R 2.75 and L 1.75 > however it's not clear whether that was a "real" change or whether it > was a temporary change caused by the soft contacts. I suspect those numbers because a soft lens normally doesn't cause that kind of shift, unless you're wearing it night and day. Sounds like you didn't because they were so bad. The first trial > lens that he put into my right eye felt absolutely horrible ... like it > was "popping" up every time I blinked ... RGPs are no picnic. But sometimes they are the only thing. How's your vision with glasses? What is the prescription for your glasses? w.stacy, o.d. > > Thanks for the input so far ... > > [quoted text clipped - 3 lines] > Wow. Sounds like a bad fit. I don't recall a toric soft lens fit that > couldn't get close to 20/30 or 20/25. Honestly, that's what I thought too. But according to my CL fitter, there was nothing else he could do for me. He said my only other option was to switch to RGPs ... > > I'm not sure what a K reading is, so no luck there. It's also > > difficult to say what my cylindrical error is. Last year it was about [quoted text clipped - 5 lines] > kind of shift, unless you're wearing it night and day. Sounds like you > didn't because they were so bad. Maybe not. Then again my lenses are quite thick ... I definitely didn't wear them day and night. I'm quite confident in the 4.25 and 2.25. Those numbers were determined post scleral buckle OU and have been quite stable over the past 4 years. My usual BCVA with glasses is 20/30 OU. After wearing the soft torics, my BCVA with glasses (w/ a cylinder of 4.25 and 2.25) deteriorated significantly (to around 20/60 or so). My ophthalmologist tried to correct it and came up with the 2.75 and 1.75. With that cylindrical correction, my vision was a (*very* blurry) 20/40. She played with the lenses for quite a while but nothing seemed to help, so we left it at that. To make things even more confusing (for me at least), last week I got my new glasses made (with the 2.75 and 1.75 cylinder). I haven't been wearing contacts for about 3 weeks straight. My vision can again be corrected to 20/30 with these new glasses ... Is it possible that the contacts temporarily induced an irregular astigmatism that couldn't be corrected properly? Alternatively, is it possible that my astigmatism changed so drastically within the course of a year? I think this is going to drive me insane. :S > The first trial > > lens that he put into my right eye felt absolutely horrible ... like it > > was "popping" up every time I blinked ... > > RGPs are no picnic. But sometimes they are the only thing. How's your > vision with glasses? What is the prescription for your glasses? As I said above, my BCVA with glasses is 20/30 OU. My Rx R -15.50 and L -15.00. The situation has been very frustrating. :( Soft toric lenses, especially in high prescriptions, can indeed change the cornea, resulting in corneal warpage. In fact, there is one study showing that the corneal warpage due to soft toric lenses can take months to resolve completely. With a prescription in the range of -15.00 with high astigmatism, I would also recommend an RGP lens, preferrably of hyper-DK material, such as Optimum Extra, Boston XO, or Menicon Z. DrG I'd go along with Dr. L. Of course the 20/60 vision with soft torics that strong coupled with 20/30 bcva now all makes sense. If rgps don't work out for you, there is always phakic iols or even clear lens exchanges. What is your age? w.stacy, o.d. > Soft toric lenses, especially in high prescriptions, can indeed change > the cornea, resulting in corneal warpage. In fact, there is one study [quoted text clipped - 6 lines] > > DrG Another idea would be to go with one of the new silicone soft sphericals and wear glasses over the cls to correct the residual astigmatism. That would be the most conservative approach, and probably my 1st choice. w.stacy, o.d. Hmmmmm .... I guess I'll have to consider that if things don't work out with the RGPs ... I wonder if my vision can get much better than what it is right now though ... :S > Another idea would be to go with one of the new silicone soft sphericals > and wear glasses over the cls to correct the residual astigmatism. That > would be the most conservative approach, and probably my 1st choice. > > w.stacy, o.d. > Hmmmmm .... I guess I'll have to consider that if things don't work out > with the RGPs ... > > I wonder if my vision can get much better than what it is right now > though ... :S Well you should be able to get slightly better acuity with contacts than with glasses, because the minifying effect of glasses is eliminated with any CLs. It would take a combo as described below, but I can't imagine not getting at least equivalent and would expect better VA. >>Another idea would be to go with one of the new silicone soft sphericals >>and wear glasses over the cls to correct the residual astigmatism. That >>would be the most conservative approach, and probably my 1st choice. I can understand your being gun shy of eye surgery, esp at your young age and history. So yea, if the rgps aren't good, try Night & Days or Purevisions, then get a careful over-refraction while wearing them. At least the resultant glasses would be weak powers, thin, non-minifying, etc. >>w.stacy, o.d. > I can understand your being gun shy of eye surgery, esp at your young > age and history. So yea, if the rgps aren't good, try Night & Days or > Purevisions, then get a careful over-refraction while wearing them. At > least the resultant glasses would be weak powers, thin, non-minifying, etc. Okay, well thanks for the suggestions (everyone)! ;) I guess I'll just have to wait and see what happens. Hopefully things will work out w/ the RGPs, but if not, I'll certainly take what you've said into consideration. =) >Another idea would be to go with one of the new silicone soft sphericals >and wear glasses over the cls to correct the residual astigmatism. That >would be the most conservative approach, and probably my 1st choice. Which, incidentally, I did for over a year. (High hyperope, moderate astigmatism). We put the sphere in the contacts and the cyl in the over Rx glasses. In my case, it worked pretty well, especially since it can be pretty tough to fit a toric scl tighly enough that it doesn't move much (inducing blur), yet loosely enough to allow good tear exchange/comfort. Something to think about.... > I'd go along with Dr. L. Of course the 20/60 vision with soft torics > that strong coupled with 20/30 bcva now all makes sense. If rgps don't > work out for you, there is always phakic iols or even clear lens > exchanges. What is your age? 21. Hmmmm ... I don't think I'd want any more eye surgery though ... I think I've had enough for a lifetime ... plus, for me, the risks are not worth it ... my fear of having more RDs surpasses my desire to have good vision. :S Is the size if the whole as large as the one my dentist puts into my wallet every six months? I would advise making a similar comparison. DrG Is the hole in your wallet the same size as the one my dentist puts in mine? DrG > Is the hole in your wallet the same size as the one my dentist puts in > mine? > > DrG Quite possibly. Luckily I don't have to worry about the dental bills just yet .... ;) > Just wondering ...in what circumstances would bitoric RGPs be required? > Are they usually difficult to fit? All I know about them right now is > that they're going to put a large hole in my wallet. ;) Usually when you have significant astigmatism. With over 2 -2.5D corneal astigmatism, a rigid lens will not fit well and the back curve of the lens needs to be made toric. That back toricity results in the contact lens not correcting the refractive error so that a compensating toric surface needs to be placed on the front of the lens as well. With today's soft toric lenses, it is possible to fit a greater percentage of astigmats with a soft lens, however, with large amounts of corneal astigmatism, vision is clearer and more stable with a rigid lens and that usually means a bitoric. Fitting bitorics requires an experienced rigid lens fitter and experience with bitorics and an accurate lab. There is often some fine tuning required in the first few months. I have fit many bitorics and the bulk of the patients are quite happy. The good news for you is that it is a one time expense. The lenses will likely last 3-5 years. Compare your cost with the cost of disposable toric soft lenses for the same time period and you won't think the hole in your wallet is so big. Dr Judy > > Just wondering ...in what circumstances would bitoric RGPs be required? > > Are they usually difficult to fit? All I know about them right now is > > that they're going to put a large hole in my wallet. ;) > > Usually when you have significant astigmatism. Hmmmmm .... > With over 2 -2.5D corneal astigmatism, a rigid lens will not fit well and > the back curve of the lens needs to be made toric. That back toricity > results in the contact lens not correcting the refractive error so that a > compensating toric surface needs to be placed on the front of the lens as > well. I see. > With today's soft toric lenses, it is possible to fit a greater percentage > of astigmats with a soft lens, however, with large amounts of corneal > astigmatism, vision is clearer and more stable with a rigid lens and that > usually means a bitoric. Anything is better than the vision I had with soft torics! If my vision doesn't improve with RGPs, I think I'll end up giving up contacts all together. :S > Fitting bitorics requires an experienced rigid lens fitter and experience > with bitorics and an accurate lab. There is often some fine tuning required > in the first few months. I have fit many bitorics and the bulk of the > patients are quite happy. Hmmm ... well my CL fitter has been at it for 22 years and, from the way he speaks, he seems to have a lot of patients wearing them ... > The good news for you is that it is a one time expense. The lenses will > likely last 3-5 years. Compare your cost with the cost of disposable toric > soft lenses for the same time period and you won't think the hole in your > wallet is so big. True. Unless my Rx changes again. :S > Dr Judy Thanks! On 15 Jun 2005 18:45:39 -0700, silverblue001@hotmail.com spewed forth >True. Unless my Rx changes again. :S You may find that your vision will stabilize once you're in a RGP or hard lens. My eyes used the same (unique) Rx for the 10 years I wore RGPs with only slight variations in my astigmatism value that didn't affect my vision or the fit of the lenses. +++++++++++++ Reply to the list as I do not publish an email address to USENET. This practice has cut my spam by more than 95%. Of course, I did have to abandon a perfectly good email account... I don't know ...I'm a bit skeptical. I can't see how a contact lens could possibly slow/stop the progression of axial myopia. Sure it could flatten the cornea and thus temporarily change your Rx ... but in my mind it seems more it's masking any changes rather than preventing them from occurring ... > On 15 Jun 2005 18:45:39 -0700, silverblue001@hotmail.com spewed forth > : [quoted text clipped - 10 lines] > This practice has cut my spam by more than 95%. > Of course, I did have to abandon a perfectly good email account... > I can't see how a contact > lens could possibly slow/stop the progression of axial myopia. Sure it > could flatten the cornea and thus temporarily change your Rx ... but in > my mind it seems more it's masking any changes rather than preventing > them from occurring ... It's more like postponing any increase that's going to happen, until you stop wearing lenses. With spherical (non toric) RGPs ometimes it does, sometimes it doesn't. I don't think bitorics offer much in that realm because they need to fit pretty much like a glove, so you can't really flatten the cornea much. w.stacy, o.d. > With over 2 -2.5D corneal astigmatism, a rigid lens will not fit well and > the back curve of the lens needs to be made toric. Wow, I'm surprise to hear that that little cyl would require a bitoric. It sounds like you fit lots of bitorics, and I can't even remember the last time I did. What's wrong with this picture? I remember fitting quite a few of them years ago, esp. in the days of PMMA, because we fit so small (8.5 mm, even less) lenses that corneal toricity did matter a lot. Nowadays, with the high DK lenses, I can fit nice big lenses that are very stable regardless of corneal toricity. I recently fit a VERY highly astigmatic keratoconus with a big spherical lens and it fits fine, and gives stable 20/20. > Fitting bitorics requires an experienced rigid lens fitter and experience > with bitorics and an accurate lab. There is often some fine tuning required > in the first few months. I have fit many bitorics and the bulk of the > patients are quite happy. I totally agree, although I don't much like the "fine tuning" idea. That's what I meant about voodoo optics. Seems like with torics predicting the result of a given lens on a given cornea is, well, a bit sketchy at best. What's the LOWEST amount of corneal toricity you will fit with a bitoric, and what's the usual diameter (or range thereof) of your bitorics? w.stacy, o.d. Even if vision is fully corrected with a spherical lens, a corneal astigmatism above 2D will cause too much rocking of the lens (with the rule) and be quite uncomfortable. It is quite simple to calculate the prescription of a bi-toric lens, just calculate the power at the axis and that perpendicular to it, then change it to its sphero-cylindrical form. The major problem is when the corneal astigmatic axis and the spectacle axis is quite a bit different. Calculation is still possible by adding the two cylinders together. An easier way to do this though, is to over-refract over a sperical lens, and give the lab the data. Roland J. Izaac > > With over 2 -2.5D corneal astigmatism, a rigid lens will not fit well and > > the back curve of the lens needs to be made toric. [quoted text clipped - 22 lines] > > w.stacy, o.d. >> With over 2 -2.5D corneal astigmatism, a rigid lens will not fit well >> and the back curve of the lens needs to be made toric. [quoted text clipped - 4 lines] > few of them years ago, esp. in the days of PMMA, because we fit so small > (8.5 mm, even less) lenses that corneal toricity did matter a lot. I've found over the years that large, spherical RGPs led to corneal molding. Also the sphericals "rock", decentre and I see more 3&9 staining. So, usually at 2D corneal cyl, I think about bitoric. Nowadays, with the high DK lenses, I can fit nice big lenses that > are very stable regardless of corneal toricity. I recently fit a VERY > highly astigmatic keratoconus with a big spherical lens and it fits fine, > and gives stable 20/20. Well, keratoconus is a different matter altogether. Though I have used bitorics on early keratoconics if there was decentration due to the eccentric cone. >> Fitting bitorics requires an experienced rigid lens fitter and experience >> with bitorics and an accurate lab. There is often some fine tuning [quoted text clipped - 4 lines] > what I meant about voodoo optics. Seems like with torics predicting the > result of a given lens on a given cornea is, well, a bit sketchy at best. Predicting is quite good if you use trial fitting lenses. I have two trial sets of spherical effect bitorics (front toric surface exactly cancels back toric so the net power effect of the lens is spherical -- greatly simplifies over refraction) one with 2D back toric (good for up to 3D corneal cyl), one with 3D back toric (good for up to 4D corneal cyl) with flatter base curve increments in 0.50D steps from 41.00 to 45.00. All are diameter 9.0, though the lab can do larger or smaller. Most of the time I can fit the exact back curve I need, otherwise I fit each meridan with the closest lens. Usually the over refraction is close to spherical, if not, I provide the sphero-cyl, with axis, over refraction to the lab and they modify the front toric to match. Can't help the fine tuning, trial lenses can only do so much. I treat the first pair ordered as trials, assess the fit and over refraction after 2-3 weeks wear then change if needed. I'm up front with the patients, tell them likely the first pair will not be the final pair and it may take two to three months of fiddling to get it right. Dr Judy What's the LOWEST amount of corneal toricity you will > fit with a bitoric, and what's the usual diameter (or range thereof) of > your bitorics? I once did a 1.50 corneal cyl due to problems with centration and comfort. Worked fine, though the lab called me to confirm that's how little I wanted. The most was 8D corneal cyl, the patient's spectacle Rx was something like +6.00 -7.00 x oblique. The 25 year old patient was very happy, as everyone else had always told him that he couldn't wear contacts and he was involved in sports. Dr Judy > w.stacy, o.d. > Most of the time I can fit the exact back curve I need, otherwise I fit each > meridan with the closest lens. Usually the over refraction is close to > spherical, if not, I provide the sphero-cyl, with axis, over refraction to > the lab and they modify the front toric to match. That's a good example of what I meant by voodoo optics. Sometimes even you let the lab figure it out, as opposed to taking your shero-cyl over-refraction and calculating everything on your own. Tricky business, esp. when the axis of the over-refraction is different from the corneal cyl axis. In the very few toric rgps I do, I prefer to over refract with a spherical trial lens, and I too count on the first custom lens as a trial lens. Now I remember why I don't like fitting the beasts. Would rather fit a tangent streak bifocal... w.stacy, o.d. >> Most of the time I can fit the exact back curve I need, otherwise I fit >> each meridan with the closest lens. Usually the over refraction is close [quoted text clipped - 6 lines] > esp. when the axis of the over-refraction is different from the corneal > cyl axis. I don't why you call it "voo doo". Yes, I do a sphero cyl over refraction, and I send that sphero cyl over refraction over to the lab, along with the power of the trial lens. Yes, I could calulate the resultant myself, and yes, it is very tricky when the axis is different. The lab has a handy-dandy computer program that figures it out and, since the lenses are computer lathed, it makes much more sense to have the lab figure out the angles. In the very few toric rgps I do, I prefer to over refract with > a spherical trial lens, and I too count on the first custom lens as a > trial lens. You really should try the spherical effect bitoric trial lenses. Most of the time the over refraction is spherical and no "voo doo" optics are required. Dr Judy Now I remember why I don't like fitting the beasts. Would > rather fit a tangent streak bifocal... > > w.stacy, o.d. > With over 2 -2.5D corneal astigmatism, a rigid lens will not fit well and > the back curve of the lens needs to be made toric. Dr Judy, are you familiar with RGP lenses made with the inner side of the OZ spherical and a periferic toric bandzone ? Nice stable fitting and no troubles for the need to compensate the toric inner OZ part, offcourse when the error in astigmatism matches the astigmatism amount of the cornea. Only possible in lower astigmatics however. > That back toricity results in the contact lens not correcting the > refractive error so that a compensating toric surface needs to be placed > on the front of the lens as well. When you are fitting an inner toric RGP, do you follow exactly the curves off the cornea thats to say do you take the same difference in the two curves (I'll suppose you fit overall a bit flatter) Depending on the refracting index off the contactlens material I fit innertoric RGP's with the flattest BCR in the same amount as the flattest cornea radius and the steeper BCR off the innertoric about 70% off the difference in the cornea curves steeper, so fitting in one direction planparallel and in the other direction flatter. (the 70% is divided 100/refractionindex lensmaterial) If in the excample above the amount of cornea astigmatism is the same or nearly the same as the refracting error in astigmatism you have now compensated for the astigmatic error and also have a nice fitting. I'm sure you know how to compensate for the spherical part. PS, most of the innertoric RGP's I fit are off the mixed astigmatic types and often around the S+4=C-4, do you have the same experience or is this a typical Dutch issue? Greetings, SignatureJan (normally Dutch spoken) |
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