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Medical Forum / General / Vision / August 2005Adaptation to multi-focal contact lenses
What is the adaptation to aspheric multi-focal contact lenses based on? This is just a random site found with Google: http://www.3d-eye.com/3d-eye/contact_lens/multi_focal.html The video shows how refractive power is divided in the lens. How can a person see only through one portion at a time? A person cannot see through one portion of a multifocal contact lens at a time (unless they are tangent streak gas perms). The vision is simultaneous-- i.e. some light is focused at distance while some is focused at near. The resultant image is "somewhat" clear at distant and near with peripheral blurring or ghosting. Some people can adapt to the resulting image while others cannot. In my experience, if the patient's expectations are managed appropriately, and a little chair time is expended by the doctor and patient working together to get the best correction possible, most patients are satisfied. The most important part is not to expect perfect distant and near vision-- expect "good enough" acuity to accomplish everyday tasks. =========== > What is the adaptation to aspheric multi-focal contact lenses based on? > [quoted text clipped - 3 lines] > The video shows how refractive power is divided in the lens. How can a > person see only through one portion at a time? > A person cannot see through one portion of a multifocal contact lens at a > time (unless they are tangent streak gas perms). The vision is [quoted text clipped - 9 lines] > The most important part is not to expect perfect distant and near vision-- > expect "good enough" acuity to accomplish everyday tasks. When I was trying multifocal RGPs some of them DID provide perfect distant and near vision -- but only for 1 second out of 60 (against-the-rule astigmatism, apparently). Crying shame, because it was like having real eyes again :-(  SignatureCheers, Bev ==================================== Start worrying -- details to follow. > When I was trying multifocal RGPs some of them DID provide perfect > distant and near vision -- but only for 1 second out of 60 > (against-the-rule astigmatism, apparently). I'm not sure what you mean. Do you mean that you could adapt to the uncorrected astigmatism momentarily or what? By perfect distant and near vision do you mean 100% unblurred, absolutely flawless vision in both sunshine and darkness, no halos? I've been reading this thread with interest and now I'll add my comments. I have a great deal of experience in fitting aspheric multifocal RGP and soft lenses. I wear them myself, mostly RGPs as they provide, for me, outstanding vision. Generalized statement about performance are not at all useful. I have some patients who do indeed achieve uncompromisingly excellent vision at all distances. (Definition: distance and near acuity equal to or better than that achieved with spectacle lenses, no "ghost/halo" at distance under any conditions.) I myself am in that group. Most of my patients do not achieve that degree of quality of vision as there are some optical compromises, but most achieve excellent distance and intermediate vision and good to excellent near vision. (Definition: as above, nearest near point of 20/20 vision equal to at least 20cm, which may not be close enough for some people's needs.) Some people experience some degree of "ghosts/halos" in reduced lighting at distance which does not impact near acuity at all but may reduce distance visual quality somewhat and generally be a little annoying. This is far more common in soft lenses than RGP. There are many optical and eye structural issues that affect what the wearer's optical experience will be. In my practice, I'd estimate that 80% are completely satisfied, 15% live with less than optimum vision but are still quite pleased and 5% do not stay with the lenses for either comfort or optical reasons. With RGPs and carefully selected patients, the issue is more often comfort than optics. For soft multifocals, the " I think these are great!" numbers are much lower, with less than 50% achieving a visual experience approaching RGPs but 70-80% being quite satisfied. The "I give ups" are in the 20-30% range. Still, many people enjoy the freedom from multiple pairs of spectacles or the hassles of hanging readers around their necks or stuffed in their pockets and purses. With careful patient selection and doctor experience, soft multifocals are an excellent option for the "over 40's" group. And they're getting better all the time. I believe (hope, dream, loose sleep over it) that when they arrive, silicone hydrogel multifocals, due to their more stable/stiff construction may be much better. In theory, it can be done. They will need to come in a few different optic zone diameters and toric (astigmatism correcting) powers. I've found a very effective optical correction for folks with low add needs ( like up to 1 or 1.25 D) who have less than .5D astigmatism is plain old Focus Night&Day/Optix or Purevision lenses, which are somewhat aspheric by design. The experience can be enhanced by .25 more plus power in the near-dominant eye. Very, very little compromise there. --LB. O.D. Did you really mean 20 cm, or should that be 20 inches? w.stacy, o.d. > but most achieve excellent distance and >intermediate vision and good to excellent near vision. (Definition: as >above, nearest near point of 20/20 vision equal to at least 20cm, which >may not be close enough for some people's needs.) > > Did you really mean 20 cm, or should that be 20 inches? > [quoted text clipped - 4 lines] > >above, nearest near point of 20/20 vision equal to at least 20cm, which > >may not be close enough for some people's needs.) Whoops! Thanks, doc. 20"/50cm. Thanks for the post. At low illumination, when the pupil is large, the rays have to enter the retina at multiple focals, don't they. So, a probable case is something like 50% of the rays are passing refractive power A and 50% are passing power B (if it's bifocal and transition is not considered). The rays A and B are hitting the retina in at slightly different angle. You said that many patients experience no ghost/halo whatsoever. Do you have an explanation or what is your best guess, how exactly is this possible? Is there a difference between typically spherically aberrated (ex-myopic) laser operated eyes and myopic eyes with multi-focal contact lenses? Putting together 1 + 1 (if the portions are as shown in the video I posted the link to), both cases have near vision at peripheral cornea and distance vision in the center of cornea. > > When I was trying multifocal RGPs some of them DID provide perfect > > distant and near vision -- but only for 1 second out of 60 > > (against-the-rule astigmatism, apparently). > > I'm not sure what you mean. Do you mean that you could adapt to the > uncorrected astigmatism momentarily or what? No. They moved/rotated out of position whenever I blinked or moved my eyes. Every once in a while they would land in the right place purely by chance, but would move away as soon as I blinked or moved. Absolutely useless for any practical purpose. > By perfect distant and near vision do you mean 100% unblurred, absolutely > flawless vision in both sunshine and darkness, no halos? Yes, exactly that. Close-up view of the veins on leaves, distant view of the TV antennas up in the mountains. As good as I get with glasses. SignatureCheers, Bev ***************************************************** Nothing is so stupid that you can't find somebody who did it at least once if you try hard enough. > What is the adaptation to aspheric multi-focal contact lenses based on? > [quoted text clipped - 3 lines] > The video shows how refractive power is divided in the lens. How can a > person see only through one portion at a time? I guess it is a variation on the mono-vision theme - the brain is remarkably good at learning to ignore things it does not want to see... As I posted in another message on this group, I am part way through a trial of Bausch&Lomb multi-focals and I am very pleased with them. I am moderately long sighted and need a +1 add reading glasses for any significant period of close work. From the minute I put the B&Ls in I had adequate vision at all distances. For the first half hour or so, if I analysed what I was seeing objectively there was something "strange" about it - not really possible to pin it down and not unacceptable. Now, I simply do not notice it - my distance vision is probably slightly better than I was getting with varifocal glasses, my close-up vision is about the same as with varifocals. I suspect that middle-distance vision (i.e. around ten to fifteen feet) is slightly worse, though that is subjective and it is still acceptable - the television does not seem quite as sharp as it does with glasses. As others have said, it is probably very dependent on expectations - if my son who is thirty years younger than me and has 20-20 vision without glasses saw the world the way I am, I dare say he would complain. For me, following years of living with varifocals or carrying round two pairs of glasses all the time, this is wonderful - I have more than adequate vision at all distances without anything hanging on my face! It is probably also dependent on your prescription - I am moderately long sighted with just a +1 add - not too much... Other people's experience could be very different, but it is not particularly expensive to find out. Martin Bradford I have fit some version of multi-focal contact lenses for 25 years, and this is truly a golden age for the multifocal lens. The Bausch & Lomb can be "stunted" a little by putting a "low add" on your dominant eye and a "high add" on your non-dominant eye, and you get a "modified monovision" that relies on simultaneous perception at times, but allows great binocular fusion. In the hands of a skilled optometrist who loves to "play" with lenses, these products can let a good 90%+ of soft lens bifocal candidates be successful. Contrarily, a "cookbook" optometrist who reads the fitting guide and doesn't go "off-label" in his thinking might hit 50% success on his best day. They can't, except for translating (true) bifocals. All others result in out of focus paraxial rays. The "adapatation" that occcurs is some peoples' ability to ignore the blur. w.stacy, o.d. >What is the adaptation to aspheric multi-focal contact lenses based on? > [quoted text clipped - 5 lines] > > > The "adapatation" that occcurs is some > peoples' ability to ignore the blur. Not noticing the blur in certain circumstances is a different thing than noticing the absence of any blur at all (as halos around lamps for example). According to LarryDoc: > I have some patients who do indeed achieve uncompromisingly > excellent vision at all distances. (Definition: distance and near > acuity equal to or better than that achieved with spectacle > lenses, no "ghost/halo" at distance under any conditions.) In my opinion it's impossible to not see a halo around a lamp unless the halo really is very vague, but, that can not the case if 50% of the rays are contributing to the halo. Unless there is something blocking those rays. > In my opinion it's impossible to not see a halo around a lamp unless the > halo really is very vague, but, that can not the case if 50% of the rays are > contributing to the halo. Unless there is something blocking those rays. That may be true, but many people don't look at lamps or such objects that are likely to cause halos. Also, vision is probably 80% psychology and maybe 20% physics, biochemistry, physiology and neurology combined. w.stacy, o.d. > That may be true, but many people don't look at lamps or such > objects that are likely to cause halos. They don't have to be especially looked at. Unless 1) you really don't care what and how you see or 2) the vision in fact is so good that it can be called practically excellent, then you won't notice the imperfections. > Also, vision is probably 80% psychology and maybe 20% > physics, biochemistry, physiology and neurology combined. In my opinion maybe something like 70% optics, 20% neural filtering/optimization/adapting and 10% physical condition. Of course, there are exceptions, but in general (or averagely), I think the "spiritual state" can affect vision relatively little. I say this even I'm actually a supporter of great possibilities of the brain. After the optics, the sensation is heavily processed by the brain, but still, the optics are there and there are tasks not even the brain can manage. With proper tests, detailed visual qualities can be tested too, there is no need to be uncertain how one sees, it can be tested (with relatively simple methods). I agree with you regarding the relative importance of optics vs. neural adaptation. I vaguely recall some discussion of this topic during my PhD training in physiological optics. The upshot of the discussion was that precision of the optics of the retinal image is the single biggest contributor to the reported visual acuity by an observer. Sorry I cannot provide details; I've slept a few times since then. On the other hand, clinically I have seen many patients who happily accept less than optimal optics in return for convenience, etc. IMHO, it's all about pre-educating patients about what they should expect from multifocal contacts. They are not perfect but they can provide a lot of advantages that can outweigh the optical disadvantages to some people. --------------------- >> That may be true, but many people don't look at lamps or such >> objects that are likely to cause halos. [quoted text clipped - 16 lines] > need to be uncertain how one sees, it can be tested (with relatively > simple methods). > On the other hand, clinically I have seen many patients who happily accept > less than optimal optics in return for convenience, etc. IMHO, it's all > about pre-educating patients about what they should expect from multifocal > contacts. They are not perfect but they can provide a lot of advantages > that can outweigh the optical disadvantages to some people. And so I cite myself as a case in point. My Tangent Streak RGP multifocals provide incredibly precise vision from distance to about 16"/40cm. They are 50% of the time at least noticeable and 10% of the time downright uncomfortable----but I persist in wearing them because I really enjoy the convenience of great vision without spectacles. My soft multifocals (a couple of aspheric types of similar designs) provide reasonable distance and intermediate vision and fair near point optics. Sometimes I'll need +1.00 "readers" to help. They are perfectly comfortable 95% of the time, yet I prefer to use the RGPs instead. I use the soft primarily for sports and beach use mostly because critical acuity is not that important (my tennis game isn't that great and surfing/ocean swimming doesn't demand great vision) and I wouldn't want to loose/damage my RGPs! I have many patients who have very similar issues. And I will repeat that I have quite a few patients who have excellent vision at all distances---even a couple with toric soft multifocals, although I find it that much easier to achieve with RGP aspheric or segmented lenses. Sure, some people wont be satisfied with multifocal contact lenses and some "adapt" to and enjoy the freedom and deal with the compromise. And some have little or no compromise. Personally, I really dislike spectacles. Even my progressives custom fitted by the lab representative from one of the premier manufacturers. But that's me. Everyone has different needs and expectations. I makes my day interesting! Speaking of which......off to work! --LB, O.D. my clinical experience is that halos are indeed noticable but can become adapted to by many patients. i think it is an overstatement to say that uncompromising distance and near acuity equivalent to spectacles without ghost/halo is achievable with simultaneous vision multifocal contacts. it is doable however with translating RGP bifocals, but many patients cannot tolerate the discomfort of RGPs. |
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