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Medical Forum / General / Vision / September 2006astigmatism
How bad does a person's astigmatism have to be to need toric contact lenses? Someone told me it would be around a 1.25, is that true? >How bad does a person's astigmatism have to be to need toric contact lenses? It depends on one's tolerance for blur. The lowest amount of astigmatism found in most soft toric contact lenses is 0.75DC. Some custom torics will go as low as 0.50DC. I am unaware of any that go lower than that (although they may exist). >Someone told me it would be around a 1.25, is that true? I usually consider a toric on anyone 0.50DC or greater, although a lot of my patients with 0.75DC of astigmatism go around with spherical soft contact lenses. Anon E. Muss For your .50 cases would you prescribe an additional .25 sphere? I've heard that's also done for lower levels. >Anon E. Muss >For your .50 cases would you prescribe an additional .25 sphere? Almost never. Only extremely picky patients complain about not having 0.50DC of astigmatism corrected. I'm not saying many patients don't notice it -- it's just that it's a rare patient that complains sufficiently to request an attempt at correcting it. IOW, in the vast majority of cases I try a spherical lens only in patients with 0.50DC of astigmatism. > >Anon E. Muss > >For your .50 cases would you prescribe an additional .25 sphere? [quoted text clipped - 5 lines] > -- it's just that it's a rare patient that complains sufficiently to > request an attempt at correcting it. And, of course, the higher the spherical correction, the less important .5 DC. > IOW, in the vast majority of cases I try a spherical lens only in > patients with 0.50DC of astigmatism. Additionally, many of the new(er) aspheric lenses "mask" lower amounts of astigmatism and some of the si-hydros are "stiffer" and further correct small amounts of cornea -based astigmatism. The only exception I've found is low plus .75 and more ATR astigs really do need the cyl correction. Like me! I'm anxiously awaiting the Purevision Toric in MY rx---aspheric, silicone, corrected cyl-----coming to the slightly-behind-the-rest-of-the-world USA allegedly in two weeks! A multifocal version would be nice, eh? LB, O.D. [snip] >> IOW, in the vast majority of cases I try a spherical lens only in >> patients with 0.50DC of astigmatism. > >Additionally, many of the new(er) aspheric lenses "mask" lower amounts >of astigmatism So they say. I've tried Frequency 55 Aspherics on such patients in the past, and while they are nice for HEMA lenses I really question how much better they are than a regular Frequency 55 Sphere. >and some of the si-hydros are "stiffer" and further correct small >amounts of cornea -based astigmatism. > >The only exception I've found is low plus .75 and more ATR astigs really >do need the cyl correction. Like me! Younger patients tend to tolerate low amounts of cylinder more than older ones also. >I'm anxiously awaiting the Purevision Toric in MY rx---aspheric, >silicone, corrected cyl-----coming to the slightly-behind-the-rest >-of-the-world USA allegedly in two weeks! Acuvue Advance for Astigmatism don't work for you? >A multifocal version would be nice, eh? Sure! > Acuvue Advance for Astigmatism don't work for you? Nope. Only three axis available in plus powers here (of course I need one they don't make), the lens irritates the hell out of my eyes (Purevision doesn't, usually) and, even if it did work, Purevision has almost twice the oxygen perm. On the aspheric issue, the Ciba si-hydros do very well and far better than the Frequency. Besides "offsetting" the astig, you sometimes get up to a diopter (or more) of apparent add power. There are a bunch of lenses with varying degrees of aspheric e values. Sometimes they work, sometimes they don't. LB, O.D. Esmerelda via MedKB.com schreef: > Anon E. Muss > For your .50 cases would you prescribe an additional .25 sphere? I've heard > that's also done for lower levels. It is useless to add half the amount of the astigmatism to the needed spherical power of the contactlens. If you are familiar with refraction methods, think about the following. With the same amount of uncorrected astigmatism you get the same acuity in vision when the retina is placed between the two focus lines (no matter where) or just with one focus line on the retina and the other in front or rear position. Jan (normally Dutch spoken) Thank you all for your reply. >>How bad does a person's astigmatism have to be to need toric contact lenses? > [quoted text clipped - 9 lines] >of my patients with 0.75DC of astigmatism go around with spherical >soft contact lenses. > How bad does a person's astigmatism have to be to need toric contact > lenses? Someone told me it would be around a 1.25, is that true? All I have is astigmatism. I wouldn't go without correction unless it was well below 0.5D. I'm not real sure (I'm not a doc) why the torics don't go below 0.75 - maybe because they figure 0.5 can round up to 0.75 and 0.25 doesn't matter. Also, from what I understand, some amount of astigmatism is corrected by the corneal reshaping effect of even soft lenses. I'd guess that somewhere between 0.5 and 0.75 would make toric (or RGP) necessary for most people. But again, I'm just a layman who has some personal experience. -- |
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