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Medical Forum / General / Vision / May 2005LASIK eye surgery, starburst
I have already asked a bit similar type of question before, but since I was forwarded back here from elsewhere.. As many of you know, in an eye that has been treated with LASIK surgery, there is a center area (about 6mm) that has perfect refractive correction. Then there is a transition zone (about 2mm) which has a sliding correction from perfect to the old (say -5 diopters). Now, if there's a bright light (and the pupil is 8mm), what will be seen is a light with a starburst/halo around it. According to my tests and the picture I see (I have been lasered with LASIK), I believe the starburst effect I see is completely caused by the transition zone (I see also other halo layers, but they're not that bad and we can dismiss them for now). When my pupil dialates, I can clearly see that the starburst is enlarging from very small (5mm pupil) to quite big (7.7mm pupil). The starburst is identical on each lamp (I see many identical starbursts if there are many lamps). I believe the starburst arm that points directly to left is caused by the transition zone "slice" in my eye that points directly to left. If I look at light from a laser pointer I can very accurately see what's going on, the distortion is very accurate and moving head changes the distortion. What I still don't understand is how come I see starburst arms and not an even halo. Does somebody have an answer for this or even speculation? I have created a bunch of pictures that I can show and I can answer all your questions if I forgot to give you some vital information. Here is a rough approximation of how street lamps look to me (when they are not close or big enough to change to halos, where individual arms are duplicated to an even field) -> http://www.glowfoto.com/viewimage.php?img=18-161234L&y=2005&m=04&t=jpg&rand=7823 Let's say we have two video projectors with the same image pointing at the same position on a wall and the other projector would have really bad focus (somewhat similar to what the LASIK transition zone could be thought to create). Then we would have just a good image and an evenly spreaded (bad focus) image superimposed. What is the essential difference in a LASIK treated eye that creates the starbursts? PS. If there are any java (or similar) based simulations about eye and how the image is forming depending on some variables, I would be really interested to see them (I've seen only basic demonstrations with simple two-ray representation). > I have already asked a bit similar type of question before, but since I was > forwarded back here from elsewhere.. [quoted text clipped - 7 lines] > > According to my tests and the picture I see (I have been lasered with > LASIK), I believe the starburst effect I see is completely caused by the > transition zone (I see also other halo layers, but they're not that bad and [quoted text clipped - 12 lines] > even halo. Does somebody have an answer for this or even speculation? I have > created a bunch of pictures that I can show and I can answer all your > questions if I forgot to give you some vital information. > > Here is a rough approximation of how street lamps look to me (when they are > not close or big enough to change to halos, where individual arms are > duplicated to an even field) -> http://www.glowfoto.com/viewimage.php?img=18-161234L&y=2005&m=04&t=jpg&rand=7823 > Let's say we have two video projectors with the same image pointing at the > same position on a wall and the other projector would have really bad focus [quoted text clipped - 7 lines] > interested to see them (I've seen only basic demonstrations with simple > two-ray representation). Probably by examining what causes similar effects in nature would be helpful. In astronomy, such "diffraction spikes" are caused by something called the spider vanes which support the mirror in a reflecting telescope. Perhaps in the eye they are caused by the crystalline lens, or perhaps the natural irregularities of the edge of the pupil. I agree with you that they are enhanced by the edge of the ablation zone. I have seen many post-LASIK patients with starbursts. They can be made to go away by correcting the outer surface of the cornea with a contact lens. DrG > Probably by examining what causes similar effects in nature > would be helpful. If cameras, starbursts are formed in two main ways (as far as I know): first one is when the aperture is a polygon, each corner will produce one or two arms. I'm not sure, but I suspect this is an effect of diffraction. If cornea causes the starburst (which would sound perfectly logical), it may not be an effect of diffraction but just refraction (with some help from irregularities). The other method on cameras is a "star-filter" with lots of grooves. A bright point of light will spread along the grooves. This is also not the case in an eye (although I guess a RK patient might have a situation slightly similar to this). > Perhaps in the eye they are caused by the crystalline lens, > or perhaps the natural irregularities of the edge of the pupil. Since the formation of the starburst is not even and there are shorter and longer arms, it would seem to me that in my eye, some of the transition zone's outer rim has less refractive error, which means shorter arm in that angle. But the arm very near the shorter arm can be suddenly much longer, which would indicate that also something else is very essentially contributing to the effect. If the arms would be solely caused by irregularities of the edge of the pupil (which would be a nicely simple problem), then, it would seem that by compensating (or somehow fixing) those irregularities, the arms would completely go away. But that sounds impossible - where do the rays now go that travel trough the transition zone? That brings us to this question: If two patients have exactly the same values before LASIK (same refractive error, pupil size, cornea thickness, similar topography), how is it possible that the other one ends up with no starbursts at all and the other one has huge starbursts? > They can be made to go away by correcting the outer surface of the > cornea with a contact lens. How does this work? Does this lens make the outer surface relatively thicker? I have always compared the flare effects following LASIK to those produced by a small rigid contact lens. In the early days of hard lenses, this type of edge flare, or diffraction was common. A search on this term turned up this excellent monograph on LASIK aberrations: http://www.revoptom.com/archive/DEPTS/ro0200rs.htm Enjoy. DrG > http://www.revoptom.com/archive/DEPTS/ro0200rs.htm Thank you. After this I have again found new, essential information. Let me comment on this article. It is reasonably recently written, though 5 years is "too much" already, I hope there are more recent articles about the same issues with new, more accurate information. The first four visual problems mentioned are blur, fog, flare (as a diffractive effect) and soft focus. I'll make my own interpreatition. a) blur Simple spherical refractive error (too much + or -). No deviations. b) fog (from scatter) Caused by misaligned lamellar fibers in stroma (a result of microkeratome). This makes sense. My own fog effect is not so bad or terribly visible, I could live with it even if it wouldn't heal (and I believe it may well heal). c) flare (from diffraction) There is mistake in the article. It should say "temporarily by contracting" instead of "temporarily by enlarging". There is talk about surgeries without a transition zone and so on (outdated). There is no mention how the starburst arms are formed, that information is missing. It does suggest though, that non-smoothness will produce diffractive effects. d) soft focus In other words, a case where there is the good focus picture plus bad focus picture superimposed. Which is probably what is the case on almost all LASIK patients in some degree. It could be argued how much prolate/oblate will affect and so on, but my logic would say, that if there is a transition zone (or a zone with no correction) and the pupil size is somewhere near the transition zone edge, a picture with bad focus will be present. At the end, microstriae is mentioned. That makes sense as well. All in all, I found misaligned lamellar fibers and microstriae particularly interesting. About your speculation of the natural irregularities of the edge of the pupil causing the starburst effect: I suspect that is not the case. If I cover my eye with a card or look through "finger binoculars", I can simply and clearly reduce the radius of the starburst where I cover the pupil. The formation of the starburst doesn't change at all, only the radius. And when the pupil is covered from the edges, I would believe rays of light are not touching the edges of pupil. But the starburst formation stays intact. That would indicate the starburst is created in cornea. > > http://www.revoptom.com/archive/DEPTS/ro0200rs.htm > [quoted text clipped - 47 lines] > touching the edges of pupil. But the starburst formation stays intact. That > would indicate the starburst is created in cornea. If you really want an optical physicist's explanation of starbursting, then I suggest you write to Ray Applegate c/o of the University of Houston College of Optometry. The only reference sources I can find refer to edge diffraction as well as artifacts in the pathway of the light, including the crystalline lens. After the light passes through the cornea, it has to pass through the lens. One thing is absolutely clear to me, and that is the starbursting is an artifact of the LASIK surgery. Another certainty is that a properly designed contact lens will make it go away. DrG > If you really want an optical physicist's explanation of starbursting, > then I suggest you write to Ray Applegate c/o of the University of [quoted text clipped - 5 lines] > surgery. Another certainty is that a properly designed contact lens > will make it go away. Probably not relevant but I wear Focus N & Ds and only get starbursts if I squint. > Probably not relevant but I wear Focus N & Ds and only get starbursts > if I squint. Squinting and starbursts. What causes starburst in that situation? I was thinking it would be a diffractive effect caused by the eyelashes, but I was not able to proove my theory with a laserpointer light and a toothbrush. I just couldn't get long starburst arms as they occur when I simply squint. One reason may be that the brushes in the toothbrush were too thick (I did separate them a bit). Anyone have ideas? > I was not able to proove my theory with a laserpointer > light and a toothbrush. In my experiment I held the brush as near as my eye as I could, "simulating" the eyelashes, but couldn't get long starburst arms at all. My guess is that it is something other than edge diffraction, i.e. possibly some type of prism effect from the tear film as a meniscus is created along the edge of the eyelid. So, instead of diffraction, it may be refraction, with some modification or contribution by diffraction, small irregularities in the pupil, lens, etc....but, mainly refraction. DrG > possibly some type of prism effect from the tear film as > a meniscus is created along the edge of the eyelid. Sounds reasonable. This would be so easy to confirm... If there was a program for this kind of purpose. I have experimented with a software called Zemax, which is a optical designer software. I'm not sure if it is able to render "end-result" images in a "normal" way. It is full of different types of image analysis, but so far I wasn't that successful. A tear meniscus is formed at the point where the eyelid comes into contact with the ocular surface. It has a base and an apex, much like an ophthalmic prism, which causes light to be deviated. Expanding on this concept, one can also imagine the edge of the ablation zone to behave similarly. DrG > A tear meniscus is formed at the point where the eyelid comes into > contact with the ocular surface. It has a base and an apex, much like > an ophthalmic prism, which causes light to be deviated. > > Expanding on this concept, one can also imagine the edge of the > ablation zone to behave similarly. I was thinking about this. I think your theory is right, it makes perfect sense. When the lower lid is lifted, there will be a long set of few starburst rays upwards in the picture. (When the lower lid covers the pupil's bottom, there will be a pyramid of no starburst down in the picture.) Let's go further with the theory: In the eyelid experiment, why do I not see just a solid part of halo like a filled V but discreet rays instead? It makes sense that the arc length is not minimal but the rays open up a bit instead, because the lower lid is not straight (the meniscus is curved). But why can I see lets say three distinct rays, the meniscus surely doesn't have three distinct planes in that case, does it?? Perhaps eyelid as well as the ablation has an irregular border. Paul, why are you obsessing over this seemingly trivial point? If you want to get rid of this problem, then get your ablation zone blasted out to 8.0 millimeters, or get a post-refractive RGP contact lens. DrG > Perhaps eyelid as well as the ablation has an irregular border. And if this irregularity would be shaped to non-irregular, what would be the visual result? No starburst rays, but uniform halo? > Paul, why are you obsessing over this seemingly trivial point? How do you define trivial point... I understand that the science of today does not exactly know how visual problems are formed after LASIK. What is the absolutely exact cause of starburst and what would be the exact action to completely eliminate it? And how is it possible that some patients do not get starburst even if their ablation and other specifications have been the same as with the non-lucky patient? > If you want to get rid of this problem, then get your ablation zone > blasted out to 8.0 millimeters, or get a post-refractive RGP > contact lens. I may go to a corrective surgery, but that will be earilest in the autumn. And meanwhile, I want to make sure that the corrective procedure will be the best possible in Europe or so. I already have ablation zone over 8mm, though the perfect correction zone is only 6.0mm (pupils max 7.66, -5D/-5D before surgery, MEL-80 used). But also I want to just understand as much as I can about LASIK now that I have really started to study it. Why I'm interested specifically about starburst is that I find it possibly the greatest common problem of LASIK. > And how is it possible that some patients do not > get starburst even if their ablation and other specifications have been the > same as with the non-lucky patient? Perhaps your premise is wrong. DrG > Perhaps your premise is wrong. Do you mean that if the doctor or the patient claims, that there is no starburst after surgery or it is smaller than before surgery, they are not telling the actual truth? Or on the second thought, I think you mean that there will be no starburst only if the specifications are optimal already before surgery (and naturally no complications in the surgery)? We know that even with large pupils it is possible to achieve vision with no starbursts, isn't that right? Or am I wrong here - is it a certainty, that if pupil diameter exceeds the perfect correction diameter, starburst will be present? If that is the case, there is no way that time could possibly heal transition zone related starburst. I think that you are bright enough to draw the correct conclusion without me correcting the dots. The problem is "planned" vs "actual" results with respect to ablation diameter and centration. Have you requested a look at your post-operative topographies? Certainly your surgeon took post-op topographies. DrG > I think that you are bright enough to draw the correct conclusion > without me correcting the dots. The problem is "planned" vs "actual" > results with respect to ablation diameter and centration. With all respect, I don't entirely follow or understand the facts here. If you mean that my ablation diameter and centration have failed somehow, I'm not sure if that is the case. I think my doctor would say that centration is perfect in both eyes. Of course both doctor and I knew that there is a risk of not achieving blur-free vision. As far as I know it was a (high) risk only, it wasn't certain that vision will be blurred and starbursted. > Have you requested a look at your post-operative topographies? > Certainly your surgeon took post-op topographies. Post-op topographies I didn't get to take home for some reason (too bad), but I did see them at the reception. To me they look quite far from perfect but on the other hand they don't seem to relate to starburst so much (?). Topographies were very different in each eye, but the starburst is somewhat similar and even in both eyes. I should have the topographies home though and examine more carefully. I'm interested in my eyes particularly, but also in the whole field of refractive surgery, how it could be improved. > How do you define trivial point... I understand that the science of today > does not exactly know how visual problems are formed after LASIK. What is > the absolutely exact cause of starburst and what would be the exact action > to completely eliminate it? And how is it possible that some patients do not > get starburst even if their ablation and other specifications have been the > same as with the non-lucky patient? You stated the above. My answer is that you needed to check your premise, which is that patients with the same ablation and "other specifications" get different results. I am suggesting that maybe they did not have the same specifications and the same ablation. Certainly, an examination of your own post-op topographies would be a good place to start. I know that fitting a contact lens with a large optical zone has eliminated the problem in every case I have treated. Therefore, the problem is related to the size and quality of the ablation relative to your pupil size and pre-operative prescription. DrG Thank you for answering me even it's getting a bit lengthy. > I know that fitting a contact lens with a large optical zone has > eliminated the problem in every case I have treated. I'm not sure if those RGP lenses are in wide use here in Finland. At the Finnish forum I have not heard of anyone using those post-op. Either they don't know about it or they don't talk about it. Can you tell me what is the design of these lenses, are they specifically for post-LASIK use? No refractive correction in the mid 6mm and then correction at the outer rim? > Therefore, the problem is related to the size and quality of the > ablation relative to your pupil size and pre-operative prescription. I'm NOT going to sue my doctor or anything, but what is your opinion, did the doctor know already pre-op that I would have the problem and it would not heal by itself? So far I have believed, that somehow it could possibly heal by itself during 6 months post-op or so (I'm talking about the transition zone refractive error problem, not problems like Bowman's crinkles which seem to be less fatal). I had the same experience with some people in Spain. They could not obtain the lenses there, either. So, I went to Spain and brought the lenses with me. But, even then they had to come to the U.S. for further adjustments. I don't understand. Some of the lenses are very much like the lenses used to perform orthokeratology, or CRT as it is called, except that the curvatures are more extreme given the greater contour changes encountered in the post-LASIK cornea. If the problem is a very large pupil, then the optical zone needs to be about the same size in order to eliminate all of the starbursts. This means that the optical zone of the lens exceeds the ablation zone diameter. Seems like a lot of trouble just to eliminate a few spikes, although I did have a patient drive from Manitoba for that very reason. He spent two full days on the road each way. That shows how much it bothered him. My point in mentioning the contact lenses was to demonstrate to you how the solution of the problem suggests the cause of the problem. DrG > I had the same experience with some people in Spain. They could not > obtain the lenses there, either. So, I went to Spain and brought the > lenses with me. Interesting. > My point in mentioning the contact lenses was to demonstrate to you > how the solution of the problem suggests the cause of the problem. I understand. Though, it may still not reveal the whole truth. If I simply use my old -5D glasses, I get much smaller starburst (maybe 10% in diameter is left). Probably the reason for that is, then I accomodate 5D and due to the glasses being a bit away from the eye (and due to laws of optics) the starburst remains otherwise the same but reduces in size. This theory I haven't confirmed. Anyway. Thanks. I'll continue trying to figure out the details. What exactly can be anticipated, what can be healed by nature and what is simply not going to heal without actually doing something. Here is another theory: Your pupils constrict because of accommodation. Another theory is that the refraction in the peripheral cornea is corrected. However, I vote in favor of pupillary constriction. The whole truth is that if a contact lens with a large optical zone eliminates the starbursts, they are caused by the ablation being (1) too small, or (2) decentered with respect to your pupil. DrG > Here is another theory: Your pupils constrict because of > accommodation. Good theory, strong accomodation does constrict the pupil. But I tested it (with infrared camera, dark room, laser pointer, glasses): My pupil was very much dilated with or without the glasses. At the same time I could see significant difference in starburst size. Result: in this experiment the effect is not caused by pupil size. > Another theory is that the refraction in the > peripheral cornea is corrected. Yes, but this is an incomplete theory.. As the transition zone has varying refractive correction and then there is the perfect correction zone in the middle, the full explanation is missing. > The whole truth is that if a contact lens with a large optical zone > eliminates the starbursts, they are caused by the ablation being (1) > too small, or (2) decentered with respect to your pupil. That may be essentially the truth in terms of correcting the problem with contact lenses. But I'm not satisfied with contact lens correction unless it is definitely the best solution the technology of today can offer and corrective surgery is not possible. > > Here is another theory: Your pupils constrict because of > > accommodation. [quoted text clipped - 4 lines] > significant difference in starburst size. Result: in this experiment the > effect is not caused by pupil size. Unless your eyes are wired differently than the other 6 billion people on the planet (or you have a damaged 3rd nerve), if you accommodated, you constricted. Your results are simply not possible. > > Another theory is that the refraction in the > > peripheral cornea is corrected. > > Yes, but this is an incomplete theory.. As the transition zone has varying > refractive correction and then there is the perfect correction zone in the > middle, the full explanation is missing. Also incorrect. By definition there is no perfect correction in a transition zone between ideal correction and something less than that. What's the middle? Didn't you get the lesson on higher order aberrations? > > The whole truth is that if a contact lens with a large optical zone > > eliminates the starbursts, they are caused by the ablation being (1) [quoted text clipped - 4 lines] > is definitely the best solution the technology of today can offer and > corrective surgery is not possible. What I'd really like to know is why you persist on this thread, or in your case, journey. If you're not satisfied with the current state of knowledge and understanding of your problem, or can not accept the current possible fixes, then just wait another year or so. I'm sure there will be more information and fixes as you are certainly not alone. When the medical industry can find a way to entice you and suck more money out of you, you'll know. Fixing LASIK problems is becoming a profitable "after market". There's a big pool of potential customers, you know. --LB, O.D. I can understand resistance due to this thread getting quite lengthy... However: > Unless your eyes are wired differently than the other 6 billion people > on the planet (or you have a damaged 3rd nerve), if you accommodated, > you constricted. Your results are simply not possible. I did record it and I can even put it online if it would help.. The size of my pupil does not change (if it changes, it is clearly constricts less than 0.5mm or so) when putting on the glasses. And my subjective visual experience was that the picture overall reduced very slightly in size and the radius of starburst reduced to less than 30% of the state without glasses. I have also recorded my pupil when I was looking an object extremely near my eye and in that case - where I accomodated to the very extreme I could - then my pupil constricted to very small (completely different than in this starburst experiment). >> Yes, but this is an incomplete theory.. As the transition zone has >> varying refractive correction and then there is the perfect [quoted text clipped - 3 lines] > transition zone between ideal correction and something less than that. > What's the middle? What are you talking about? This is how a typically lasered eye (with today's technology) is post-op: about 6.0mm diameter of perfect correction in the middle, then about 2mm or so transition zone to the old refractive error zone (-5D in my case). > Didn't you get the lesson on higher order aberrations? I'm trying to. Don' t know enough yet, but something I do know. > What I'd really like to know is why you persist on this thread, or in > your case, journey. If you're not satisfied with the current state of > knowledge and understanding of your problem, or can not accept the > current possible fixes, then just wait another year or so. I don't want to just wait. One of the reasons is that my doctor will suggest me something in half a year (possibly a corrective surgery) and, since I feel that I can considerably affect the outcome by my own action, I want to and will make sure beforehand that I investigate the possibilities properly. Also I want to help others who are in the same situation as I were: spending lots of time to study the real possibilities, complications and rates of success and still not getting the full picture of the most essential things related to refractive surgery. > I suggest you write to Ray Applegate c/o of the University of > Houston College of Optometry. Ok, I will. Thanks! But what about this: Which is more powerful: aperture size effect itself and transition zone unmasking in terms of the radius of starburst? Apparently aperture size itself is a powerful factor to change the defocus radius, like for example according to this: http://www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?t=55 How is it possible that a person with large pupil and transition zone will see no starburst (or halo)? > How is it possible that a person with large pupil and transition zone will > see no starburst (or halo)? It is possible when the pupil is smaller than the ablation zone. A transition zone is designed to minimize pupil-dependent aberrations while sparing corneal tissue. No laser manufacturer will claim that pupil-dependent aberrations will be totally eliminated. DrG > It is possible when the pupil is smaller than the ablation zone. A > transition zone is designed to minimize pupil-dependent aberrations > while sparing corneal tissue. No laser manufacturer will claim that > pupil-dependent aberrations will be totally eliminated. Hmm. I don't mind if the surgery didn't have 100% perfect result, but if there was even no chance whatsoever that there would be a starburst and "fog" free vision, then I have to say it's not quite right. I have heard and continue to hear that people have got completely halo free vision. And many sources say that vision will or at least may get better over time. Some sources even say that halos are not necessarily produced by the transition zone but only made worse by large pupils (which I find a bit off). Do you think that problems related to pupil exceeding the perfect correction area (typically 6.0mm) have no basis to heal over time? > I don't mind if the surgery didn't have 100% perfect result, but > if there was even no chance whatsoever that there would be a > starburst and "fog" free vision, then I have to say it's not quite > right. By "quite right" I meant it's not very nice or fair. Did you mean to say "no chance," or "a chance"? If you thought there would be no chance of any night vision disturbances, then I am afraid you didn't read the fine print of the informed consent. DrG > If you thought there would be no chance of any night vision > disturbances, then I am afraid you didn't read the fine print of the > informed consent. No no, I thought there would be a chance of getting NO night vision disturbance (and a chance of getting NO "fog" disturbance in room light). But from what you wrote I figured that in your opinion there was no chance of night vision disturbance free vision (simply because max pupil is way over perfect correction area). To make myself even clearer, what my doctor claimed was that only 25% of his patients have reported ANY kind of night vision disturbance and many have reported better night vision that pre-op. Just to clear what I meant to say. Let me make it clear that I don't know your scotopic pupil diameter, and I don't know the specs on your ablation. All I know is that starbursts go away when the pupil shrinks or an RGP lens with a large optical zone is fitted. That pretty much proves that the size or location of the ablation are the issue. DrG > All I know is that starbursts go away when the pupil shrinks > or an RGP lens with a large optical zone is fitted. I do understand, agree and believe in this perfectly. It is extremely easy to experiment this. But if somebody is reading this, I just want to point out that several studies insist that a large pupil is not "a major risk factor" for night vision problems. This sounds strange to me, and in my subjective experimentation I would say this is definitely wrong. But this is what is said in many publications. http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=1 4711706&dopt=Abstract http://www.opt.uh.edu/research/voi/WavefrontCongress/2004/presentations/27BRADLEY.pdf Earlier from this thread: "> How is it possible that a person with large pupil and transition > zone will see no starburst (or halo)? It is possible when the pupil is smaller than the ablation zone." Seems to me that there is a clear contradiction. According to the publications it is also possible when the pupil is larger than the perfect correction zone. From 27BRADLEY.pdf: "Such data will also help resolve the intriguing question of why NVC seem to disappear in many post-RS patients (e.g Schallhorn et al, 2003, Lackner et al 2003). Is it neural adaptation (Webster et al, 2002; Artal et al, 2003), pupil adaptation (Woodhouse, 1975) or structural/optical adaptation (Klyce, 2004)?" Yes, that is the intriguing question. Neural adaptation? I don't think so. I do believe and realize that brain has superb filtering capacity, but I just don't understand how brain could filter the correct image that is lost behind disturbance of relatively very high brightness (as a short explanation). Pupil adaptation? I don't think so, but come on, this should be ridiculously easy to confirm. Structural/optical adaptation? I don't know what that is. Out of these three "explanations" this sounds the most reasonable though. I think it depends on your definition of "major risk factor". Typically, in medicine, such wording tends to be reserved for disastrous outcomes as opposed to "mild or moderate problems" which tend to be dismissed as normally expected things. Tough to quantify these things. w.stacy, o.d. >>All I know is that starbursts go away when the pupil shrinks >>or an RGP lens with a large optical zone is fitted. [quoted text clipped - 42 lines] > Structural/optical adaptation? I don't know what that is. Out of these three > "explanations" this sounds the most reasonable though. > I think it depends on your definition of "major risk factor". > Typically, in medicine, such wording tends to be reserved for > disastrous outcomes as opposed to "mild or moderate problems" which > tend to be dismissed as normally expected things. Tough to quantify > these things. Ok, but if starburst clearly increases radius from 5% (being not disturbing at all) to 100% (being very disturbing, easily covering the car behind it) when pupil dilates from 5.5mm to 7.66mm, I would say that based on this simple observation pupil size is clearly a "major risk factor" (this term is a direct citation from the PubMed link I previosly pasted). Very simple. The publications seem to insist that there is a natural healing process that will correct the disturbance or the disturbance is not there in the first place even if the pupil size is way over the perfect correction zone. Well, the average scotopic pupil size seems to be about 7.0mm. This means that most patients will have larger pupil than the perfect correction zone. Deriving from this we could say that most patients don't get the best possible result. And therefore, in most cases it really doesn't matter what the scotopic pupil size is - the result will be distorted anyway. Is this the logic behind those publications?? Would be very strange to me if it is. I think that night vision disturbances after LASIK are not rare at all. It it was rare, there wouldn't be so many studies about it. DrG > I think that night vision disturbances after LASIK are not rare at all. > It it was rare, there wouldn't be so many studies about it. We often hear statements like: with time and healing, the effect goes away." The post-LASIK: don't worry, you'll be fine. And of course the pre-LASIK mantras: "This is the best thing you've ever done for yourself." "You can wake up in the morning and see the alarm clock!" "You can throw away your eyeglasses and forget the hassle of contact lenses." Well we know that none of that is really very honest. The reality is that a substantial number of LASIK'd eyes will experience any one of , or multiple, notable optical artifacts and distortions. The time and healing thing? Our minds are really good at tuning out constant neurological errors, pain, disabilities. That doesn't mean that they're not there or affecting the quality of life. It's a psychological adaptation and thank goodness for that! A lifetime myope who spent thousands of dollars on surgery and can see reasonably well without optical correction but has (even serious) aberrations in their optics is not going to tell their friends that they screwed up and made a horrible mistake. That is simply not psychologically tolerable. They adjust, they accept their fate and move on. Or they take anti-anxiety medications. In some case, stronger drugs. Or they begin the continual pursuit of fixes for their post-LASIK problems. And the medical industry will try to oblige as there's plenty of money to be made on post-LASIK patients. --LB, O.D. Yup. I think you nailed it pretty well, Larry. Have laser, will travel. By the way, have you purchased yours yet? I'm thinking about getting one. Any recommendations? DrG > Yup. I think you nailed it pretty well, Larry. Have laser, will > travel. > By the way, have you purchased yours yet? I'm thinking about getting > one. Any recommendations? I going to wait for the big blow-out discount clearance sale later this year, meanwhile researching using the laser to remove warts on the the frogs that plague my garden. I understand they are developing algorithms to remove blemishes from fruit and vegetables so that it will sell better. I plan on opening a chain of Good As New! Clear Your Fruit service centers. --LB, O.D. All kidding aside, Larry, there is a serious side to this topic, which is the retreatment of higher order aberrations created by LASIK with another laser procedure. If it works, great. If it doesn't work, the patient can wind up worse off in my experience. Sometimes, far worse. On the other hand, a contact lens fix will virtually never makes the patient worse than before. DrG > All kidding aside, Larry, there is a serious side to this topic, which > is the retreatment of higher order aberrations created by LASIK with > another laser procedure. If it works, great. If it doesn't work, the > patient can wind up worse off in my experience. Sometimes, far worse. It is that last sentence that sends chills up my spine. > On the other hand, a contact lens fix will virtually never makes the > patient worse than before. Absolutely, and technology is heading the right direction. Sadly it had to be market-driven, but none the less the right direction. And for those LASIK's folks with problems, my posts on the subject, kidding or not, should not be taken as a lack of concern for your plight. I can only imagine what it must be like to excitedly go through a procedure that's supposed to vastly improve the quality of life and have it go the other way. I certainly hope that a fix is available for you and that other people can avoid poor outcomes. LB, O.D. "Dr. Leukoma" <drg@leukoma.com> wrote in news:1115389308.048631.41850 @z14g2000cwz.googlegroups.com: > On the other hand, a contact lens fix will virtually never makes the > patient worse than before. > > DrG But, the patient had surgery in the first place to avoid the contact lens. I guess each patient needs to assess the degree of risk threshold on their own. Scott Yes, and that certainly poses a psychological barrier to a number of patients. On the other side of the coin, many patients also become rather "gunshy" about future surgeries as a result of a bad experience. DrG I'm not so sure about that. It seems that since the flap never really "heals", and all lasik eyes are more prone to DLK development than normal eyes, and the sudden development of late dlk (many years later, maybe forever, which can be serious) can apparently be stimulated by even minor epithelial insult, such as might be caused by RGP wear, I'm beginning to get a bit uneasy about recommending lasik to *anyone*. Anybody want to comfort my uneasiness? w.stacy, o.d. > All kidding aside, Larry, there is a serious side to this topic, which > is the retreatment of higher order aberrations created by LASIK with [quoted text clipped - 5 lines] > > DrG I've never seen it happened, and I've fitted quite a few post-LASIK patients. I've even had a a few put their Macrolens in their eye with cleaner, thinking that it was wetting solution. I think the DLK scare is a bit overblown. DrG There is nothing wrong with being uneasy about LASIK. It shows a competent level of understanding. The LASIK flap does heal, but not like a cut on your arm. We have a detailed article on this at http://www.usaeyes.org/faq/subjects/complete.htm Late term DLK does occur, but I have never seen even an anecdotal report of DLK due to RGP contact lens wear. Normally it is due to a significant insult to the eye. All patients need to understand that once they have had LASIK, they have always had LASIK. Whenever they receive trauma to the eyes, they need to be checked by an eye doctor as well as a general physician. The limitations and complications of the LASIK flap continue to keep pressure on the use of surface ablation techniques. PRK may work fine, but is uncomfortable for the patient and corneal haze with higher corrections is a problem. Haze can be controlled with vitamin C supplements and application of Mitomycin C, but no one knows just how far one can go using just vitamin C, and Mitomycin is strong medicine that may be appropriate when needed, but probably should be avoided whenever possible. LASEK attempts to save the epithelium to reduce discomfort and haze, but most the cells die from the alcohol solution used to dislodge them, and nothing has shown a significant difference in rate of haze due just to the epithelial flap. Epi-LASIK is the latest in the attempt to make PRK with the same Wow! factor as LASIK, but it is too new to really be proven. Interestingly, Epi-LASIK was developed by the same doctor who developed LASIK. Apparently after all these years and millions of patients, he has changed his mind. Or at least, redirected it a bit. Glenn Hagele Executive Director Council for Refractive Surgery Quality Assurance Email to glenn dot hagele at usaeyes dot org http://www.USAEyes.org http://www.ComplicatedEyes.org I am not a doctor. I just happened to be listening to an audio-digest ophthalmology report as I was driving home last night and David Hwang, M.D. (ucsf sch med) was reporting on some cases of "late onset DLK". According to him, the flap never really heals, and can be lifted many years out, and can be very subject to epithelial disruption, esp. if there was any epith. disruption during the original lasik. He also mentioned that fluid can accumulate in the interface which can falsly lower the iop reading, even causing a glaucoma to look like uveitis or corneal dystrophy. He also said that wave front can screw up if the surgeon isn't paying attention, citing a case where the pt had sat around for a while after fluress was used, causing drying and deformation of her cornea, which was then mapped by the laser, and you guessed it, she got a nice reverse imprint of that dried cornea on top of the refractive fix. My unease grows. w.stacy, o.d. > There is nothing wrong with being uneasy about LASIK. It shows a > competent level of understanding. [quoted text clipped - 41 lines] > > I am not a doctor. I defer to our detailed article on the issue of flap healing, but all other issues are spot on...and all boil down to the quality of the doctor. These are all issues that had been published some time ago that any refractive surgeon worth his/her microkeratome should know about, know how to prevent, know how to treat, or know how to advise the patient BEFORE that patient makes a decision about elective surgery. Glenn Hagele Executive Director Council for Refractive Surgery Quality Assurance Email to glenn dot hagele at usaeyes dot org http://www.USAEyes.org http://www.ComplicatedEyes.org I am not a doctor. I can't deny that late onset DLK doesn't occur, just that I haven't seen it in conjunction with post-LASIK contact lens wear, and I've published the largest such study to date. Also, I've seen studies involving ortho-k after LASIK, without mention of a single complication. Of course, the point is not to withold necessary contact lenses, but to avoid the complications with proper fitting. When I get my new website up and running, I will have a powerpoint PDF with some nice examples. DrG Have you tried the macrolens? w.stacy, o.d. > I can't deny that late onset DLK doesn't occur, just that I haven't > seen it in conjunction with post-LASIK contact lens wear, and I've [quoted text clipped - 7 lines] > > DrG Have I tried the Macrolenses on myself? No. On other patients, yes, of course. Many times for post-RS, some keratoplasties, cones, and others for whom RGPs might be indicated but otherwise have a low tolerence for corneal lenses. Pluses and minuses, as with anything. DrG I've enjoyed this epic thread mainly because starbursts have been my bane since having LASIK seven years ago. I recently had a thorough checkup. The doctor did not believe my small ablation zone was the reason for starbursts. I noticed the aberrometer result was a blue ball with red spots. The red spots radiated starbursts very much like the starbursts I see daily. The tech commented that he'd never seen rays that large. He called this "higher order aberrations" but didn't explain it. Are the starbursts symmetrical, or radiate in one plane only? Generally speaking, the starbursts will be oriented 90 degrees away, or perpendicular to any ridge of tissue such as striae or other. It is due to the prism effect. DrG > Generally speaking, the starbursts will be oriented 90 degrees away, > or perpendicular to any ridge of tissue such as striae or other. It > is due to the prism effect. In my fascinating dark bathroom and a laserpointer experiment I see very long vertical (or slightly opened to X) rays when squinting. Now I noticed that when squinting I also see extra horizontal (or whisker-like) rays, but they are much shorter than the horizontal ones. This also happens outside at bright daylight when squinting and looking at something that reflects bright sun light. The prism effect (?) caused by squinting apparently causes both vertical and weaker horizontal rays (but not rays of full circle). Post-LASIK starburst apparently commonly consists of rays of full circle like it is pre-op without spectacles. Another thing I was thinking is that maybe the shape of the edge of pupil does have one relation to post-LASIK starburst: possibly the outer edge of the starburst or halo is identical to the pupil shape (which is not a perfect circle)? Or actually it definitely is like this, I'm just not sure how much cornea affects the *outer edge shape* of the starburst as well. > Another thing I was thinking is that maybe the shape of the edge of > pupil does have one relation to post-LASIK starburst: possibly the > outer edge of the starburst or halo is identical to the pupil shape > (which is not a perfect circle)? Now I take back what I wrote there. I didn't find clear relation between my pupil shape and the outer shape of the halo I see. Actually my pupil is quite a clean circle (though I don't have too good measuring equipment here). And the halo I see is very far from being a clean circle. So, I suspect pupil shape does also define the halo outer shape, but aberrations in the cornea are what mainly produce the shape of the halo. For me the largests rays are in a "V". But a lot of different smaller rays extend all around the light source. With RGP lenses the rays are uniformly smaller but still there. I was struck how the aberrometer rays radiating from the red spots had a similar pattern to the largest rays of my starbursts. > For me the largests rays are in a "V". DrG will probably suggest it is because of decentration of ablation. Which can very well be true. However, research by Reinstein seems to favor the idea that surface topography does not (necessarily) reveal all the essential aberration related information and thus an apparent ablation decentration isn't necessarily what really has happened. > I was struck how the aberrometer rays radiating from > the red spots had a similar pattern to the largest > rays of my starbursts. Probably many at here can guess what kind of measurement you are talking about, but could you explain to me which exact aberrometer was in use and what kind of results does it give? Links to articles are welcome as well. I don't know the proper name for the device. I was told it read aberrations. What I saw was a printout of a blue ball 7 or 8cm in circumference. Within the blue were several small reddish dots 2-5mm in size. Some of the dots had red rays radiating from them. The rays extended well beyond the rim of the blue circle. The pattern of these rays looked similar to my starbursts. The tech pointed at the rays and said "These are the higher order aberrations". He also said he had never seen rays extend so far beyond the edge of the blue. > > For me the largests rays are in a "V". > [quoted text clipped - 11 lines] > about, but could you explain to me which exact aberrometer was in use and > what kind of results does it give? Links to articles are welcome as well. DrG isn't suggesting anything of the sort. Topographies can indeed be very revealing. What they do NOT reveal is aberration-related information. There is, however, a correlation between aberrometry and topography following refractive surgery. If some refractive surgeons had paid closer attention to topography, some of their wavefront-driven corrective surgeries would have been more successful. I believe that the consensus is that wavefront aberrometry does not tell the whole picture in highly aberrated corneas. A picture is worth 1,000 Zernicke polynomials. DrG >> DrG will probably suggest it is because of decentration of ablation. > > DrG isn't suggesting anything of the sort. I suspected so because you said in the IntraLase thread: "The tail of the comet is typically opposite to the direction of decentration. This may not always be the case, since other aberrations may be superimposed." > Topographies can indeed be very revealing. What they do > NOT reveal is aberration-related information. I have to admit, I haven't found really good information about the relationship and practical differencies between topography and wavefront. I will read it thoroughly once I find it. But what does topography reveal if not aberration-related information? > A picture is worth 1,000 Zernicke polynomials. Sounds very reasonable, but what kind of picture do you mean? Oh, there are tons of stuff out there on the internet about topography and wavefront. Topography is extremely useful in evaluating the quality and size of the ablation, and to document features such as central islands, decentered ablations, small ablations, etc. There are also references to decentered ablations inducing coma, and to oblate corneal shapes inducing spherical aberration. Even I published an article in the January edition of Eye & Contact Lens showing how the corneal shape could be remodeled with a contact lens and the changes in aberrometry that result. In my powerpoint presentation, I even show in detail how to reduce spherical aberration by changing the corneal profile. I also show a case of a central island on topography being missed on aberrometry. Most experts agree that wavefront does not provide a full picture of a complicated post-refractive cornea. I hope you get your problem resolved. Perhaps the starbursts will diminish in time, or you will learn to ignore them. DrG > I hope you get your problem resolved. Thank you. I also hope that eventually all of this becomes non-controversial and that accurate measurement and predictable laser treatment becomes available for everyone. > Perhaps the starbursts will diminish in time, or you > will learn to ignore them. So far the only theory - that I encountered - on how this (possibly simple) case of peripheral area induced starburst could possibly diminish in time is that stroma would grow in thickness in the peripheral area. About the psychological aspect and the filtering capabilities of brain. I'm not sure if I wrote this here already, but in my opinion it is impossible for the brain to ignore distortion if it is severe enough. In a simple case at night, when there is a very dark car and very bright headlight, the starburst is obviously tremendously brighter than the car behind it. Also because the retina has a strong adaptive nature, the result is that the information that is hidden behind the starburst is simply lost and there is no algorithm that could possibly effectively extract that information. Of course for example minor floaters are a completely another thing: they are often at different locations at different eyes and only mask the image slightly -> it is relatively easy for the brain to filter them out (or simply not bring attention to them). One more thing I want to point out here: for me, the biggest problem isn't night time starbursts (although they are disturbing enough to clearly lower the safety at night driving) but rather the fog or blur in room light, induced by the same exact thing as starbursts. I don't see refractive surgery ever becoming totally predictable because the eye itself is not static and the cornea is not a piece of plastic. Also, I was unaware that your vision was foggy and blurry in normal room illumination. You seem to be having more than one side-effect. When are you going to proceed from intense self-analysis to getting a second opinion? Even with medical training, doctors need to consult with other doctors for their own health issues. DrG > Also, I was unaware that your vision was foggy and blurry in normal > room illumination. You seem to be having more than one side-effect. Actually my point was trying to be, that I believe that my foggy vision (and difficulties in reading music scores) in normal room illumination is fully or at least essentially because of the same exact problem as with starburst. Simplest explanation to this is that measuring pupil size with a video camera I can see that there is only minimal foggyness or blur around white objects on black background when the pupil is only around 5mm in size (and my scotopic was 7.66mm). And, as I've stated, the fog-blur radius is the same as starburst radius. It's the same thing. One little light dot causes starburst, a line of dots cause a line of blur (which actually consists of starbursts blended together side by side). > When are you going to proceed from intense self-analysis to getting a > second opinion? Just as a possibility, I don't know yet, I may consider going to Mr. Reinstein if he's willing to check me out. My own doctor will check me the next time in autumn but before that I just want to make sure I know the basics myself and that I know what are the possibilities worldwide (in case there is better equipment or knowledge outside my country). Naturally I have been in topography (1 month post-op) but there is currently nothing that my doctor can do because the vision may change and it is not wise to do retreatment yet because of that. I just popped back to your previous posting on this issue, and you previously dismissed the fogging as being insignificant. Now you say the it is now the bigger problem. What's going on here? DrG > I just popped back to your previous posting on this issue, and you > previously dismissed the fogging as being insignificant. Now you > say the it is now the bigger problem. > > What's going on here? It seems that this format of a long conversation in a news group is a bit restricting and leaves room for misunderstandings and statements are often made with only minimal explanation. I suspect that minor Bowman's cracks and misaligned lamellar fibers in stroma cause a wide scattering and while it may be visible around lamps at dark, it is only minor compared to spherical aberration induced starburst/halo that is caused by too small fully corrective ablation zone. An image would clarify what I mean (pointing out what distortion is probably caused by what aberration). I know I used the term fog confusingly, sorry about that. Minor Bowman's cracks? Those should be able to be identified with a slit lamp. As I recall, your prescription wasn't too high. But, was your cornea excessively flat? In all likelihood, a good examination along with good topographies will reveal the source of the problem. Wavefront? I rather doubt it. Wavefront jargon seems to have cast more of a fog rather than a light on some of the problem cases. All I know is that contact lenses can reduce the higher order aberrations after LASIK by almost 80%. One or more of those aberrations is responsible for your problem. What this means is that most of the problems are with the surface. DrG Minor Bowman's cracks? Those should be able to be identified with a slit lamp. As I recall, your prescription wasn't too high. But, was your cornea excessively flat? In all likelihood, a good examination along with good topographies will reveal the source of the problem. Wavefront? I rather doubt it. Wavefront jargon seems to have cast more of a fog rather than a light on some of the problem cases (I am not a paid consultant to a laser manufacturer, by the way). All I know is that contact lenses can reduce the higher order aberrations after LASIK by almost 80%. One or more of those aberrations is responsible for your problem. What this means is that most of the problems are with the surface. DrG Minor Bowman's cracks? Those should be able to be identified with a slit lamp. As I recall, your prescription wasn't too high. But, was your cornea excessively flat? In all likelihood, a good examination along with good topographies will reveal the source of the problem. Wavefront? I rather doubt it. Wavefront jargon seems to have cast more of a fog rather than a light on some of the problem cases (I am not a paid consultant to a laser manufacturer, by the way). All I know is that contact lenses can reduce the higher order aberrations after LASIK by almost 80%. One or more of those aberrations is responsible for your problem. What this means is that most of the problems are with the surface. DrG > Minor Bowman's cracks? Those should be able to be > identified with a slit lamp. The only thing that was slightly visible with the slit lamp was a short bit of the flap seam in the other eye. > But, was your cornea excessively flat? Excessively oblate or excessively thin? The thickness I don't remember, it was told very quickly only. But it was ok, somewhere around the average 545 microns. My doctor says night vision may degrade temporarily for 3-12 months (while permanently it'll be a problem for 1-2%). I'm still trying to find out what can heal during these 3-12 months that will remove the problem. Schallhorn, et. al. suggest that NVD improves by six months. I've not heard or read anything to suggest that NVD worsens after 3 months. Also, my impression is that more than 1 or 2 percent of patients have permanent NVD. But, if you are as good a researcher as I think you are, you already know this. Corneal healing is most active at 3 to 4 months following surgery. DrG We have had patients contact us whose night vision problems worsened after 1-3 months, but it was able to be attributed to an additional event such as edema, regression, medication response, etc. I do not know of an instance wherein night vision problems that were induced solely by refractive surgery worsened after three months. Glenn Hagele Executive Director USAEyes.org "Consider and Choose With Confidence" Email to glenn dot hagele at usaeyes dot org http://www.USAEyes.org http://www.ComplicatedEyes.org I am not a doctor. > Ok, but if starburst clearly increases radius from 5% (being not disturbing > at all) to 100% (being very disturbing, easily covering the car behind it) > when pupil dilates from 5.5mm to 7.66mm, I would say that based on this > simple observation pupil size is clearly a "major risk factor" (this term is > a direct citation from the PubMed link I previosly pasted). Very simple. I see this thread is long, and I'm in on the tail end of it, but I'm curious what you mean by the 5% and 100% and "radius" above. If you are talking geometry, then the distance from the center of the light to the outer edge of the starburst "rays" would be twice the radius of the light source, or what? That can't be what you mean, because the starburst of a headlight would have to be many times larger than the headlight to cover an entire car, maybe 10 times or 1000% larger. > The publications seem to insist that there is a natural healing process that > will correct the disturbance or the disturbance is not there in the first > place even if the pupil size is way over the perfect correction zone. Time can heal a lot of things, and a lot of it is psychology. That is, some people are very annoyed by what others may see as trivial, or not even notice, and vice-versa. I think if you carefully queried those with "perfect" lasik results, you'd be able to elicit some star-bursting, some haloing, and the rest. lasik is never "perfect", no surgery is. w.stacy, o.d. > I see this thread is long, and I'm in on the tail end of it Doesn't matter, maybe we are actually getting somewhere. :) > I'm curious what you mean by the 5% and 100% and > "radius" above. If you are talking geometry, then the > distance from the center of the light to the outer edge of > the starburst "rays" would be twice the radius > of the light source, or what? I have created somewhat accurate images that represent my vision in different kind of situations. I can put them online at some point if necessary. By 100% I simply mean that it is the maximum size of the starburst (which is identical to the blur size that was present in my non-corrected eyes pre-op when pupils were at maximum). And 5% is linearly 5% of that 100%. The easiest way would be to give the accurate images to avoid confusion. Anyway, as we know there are lots of starburst images on the net, which are similar (but most of them are somewhat badly drawn if I might add). > lasik is never "perfect", no surgery is. Maybe not perfect. But I have heard and continue to hear that patients claim _less_ starbursting and halos post-op than pre-op. I know that I should interview them really carefully and so on, but at least this is what many patients report. By the way, this is one of the reasons why I'd like to get to the bottom of this - people don't have proper reference point, they don't know how to evaluate their vision and therefore subjective results are not accurate. There has to be clearer means to evaluate vision so that real success rates can be published. But, of course, we have to remember that overall it can be better for the patient to have a moderately distorted lasered eyes than half blind -10D eyes (but certainly we shouldn't stop aiming for the best possible results). > By 100% I simply mean that it is the maximum size of the starburst (which is > identical to the blur size that was present in my non-corrected eyes pre-op > when pupils were at maximum). And 5% is linearly 5% of that 100%. I don't think that's a good way to "measure" the extent of starbursts. Since it's inherently a subjective symptom, there may be no good way to do it, but I think maybe relating the diameter of the starburst to the diameter of the light source would be a way to do it. (like in your case, maybe 10x . Of course this doesn't say anything about the intensity or density of the thing. Maybe a standardized test could be devised that presents a bright light in the middle of a snellen chart and compares readability with it on and with it off? > Maybe not perfect. But I have heard and continue to hear that patients claim > _less_ starbursting and halos post-op than pre-op. I know that I should > interview them really carefully and so on, but at least this is what many > patients report. I think they might be doing what you are doing above, comparing pre-op uncorrected vision with post-op. A better comparison would be pre-op best corrected vision with post-op. Most people would report little or no starbursting pre-op with best Rx (except contact lens wearers, who sometimes get it). > By the way, this is one of the reasons why I'd like to get to the bottom of > this - people don't have proper reference point, they don't know how to > evaluate their vision and therefore subjective results are not accurate. > There has to be clearer means to evaluate vision so that real success rates > can be published. Agreed, as above. > But, of course, we have to remember that overall it can be better for the > patient to have a moderately distorted lasered eyes than half blind -10D > eyes (but certainly we shouldn't stop aiming for the best possible results). I'm not so sure about that. I don't much care for any outcome that results in permanent, unfixable distortions. But then some people will accept it to get rid of their dependence on glasses/CLs. Those people must be warned repeatedly about what they are in for. I'm leaning more towards IOLs for the high myopes and all hyperopes. w.stacy, o.d. > I don't think that's a good way to "measure" the extent of starbursts. That was just an example to show how simple it is to discover that starburst radius is dependent of pupil size. > Since it's inherently a subjective symptom, there may be no good way > to do it, but I think maybe relating the diameter of the starburst to > the diameter of the light source would be a way to do it. The easiest and most accurate way is to have a software that is very well designed to create (or even calculate) visual distortions. Some of the simple flash based widgets on the net are ok for that, but very limited. We can also simply measure distances (the distance to the lamp and the radius of starburst in meters for example). The radius can be measured with a computer screen too (with a software or just measuring the sizes and distances). Anyway, there can be very accurate ways to describe how exactly the distortion looks like. It is really not that "psychological". Of course it makes no sense to pay attention to distortions in every day life if they don't actually bother in any way, but for measurement purposes we can very well and accurately do it. > Maybe a standardized test could be devised that presents > a bright light in the middle of a snellen chart and compares > readability with it on and with it off? Why not, for example. Certainly in the early days of contact lenses, the infamous "ring scotoma" of the miniature PMMA lens was accepted as part of the experience. However, I must say that if one objected to it, one could always go back to eyeglasses. Eventually, technology would make it possible to increase the diameter of both the contact lens and the optical zone, with the result that the "ring scotoma" would become less intrusive. I might add that the typical optical zone of today's RGP lenses is 7.6 mm, and the typical optical zone of soft lenses is 8.0 mm. Probably a few people with extra large pupils will report NVD with those diameters. There are even people with large pupils and oblate corneas who have not had LASIK and have NVD. I still wonder to this day where the excimer laser engineers had their heads when they designed such small optical zones. The only thing that I can think of is that the marketing people had the most influence, and not the engineers. DrG > I still wonder to this day where the excimer laser engineers had their > heads when they designed such small optical zones. The only thing that > I can think of is that the marketing people had the most influence, and > not the engineers. OK here I can chime in. They designed small optic zones because they wanted to correct higher orders of myopia. Like -10 So if you're gonna do the high myopes, you need to keep the ozd small so you don't burn through the cornea, right? I mean if you're only -1.00, then you can afford a 10 mm ozd, because at the thinnest, you'll only be maybe .5 mu thick? But if you're -10, with a 6 mm ozd, you're burning through a lot of cornea. maybe too much. maybe the eye will break. So you establish a "standard" ablation zone, so the zealots don't blind too many eyes in the process...????? w.stacy, o.d. w.stacy, o.d. Naturally, which is why I think that the marketing people had the upper hand -- to appeal the broadest possible range of myopes. DrG The first study was a retrospective study. I wonder about the accuracy of pupil size measurement in 1999. Possibly the data was confounded. There is much controversy surrounding the issue of pupil size and night vision disturbances. On the other hand, I certainly know how to make it go away optically. I have done serial studies on the same patient with the optical zone of the contact lens as the independent variable and halos/starburst as the dependent variable. I have even had the patient evaluated by an independent source with wavefront studies. DrG |
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