- Email: [email protected]
Session II: clinical management and vision
SESSIONI: BACKTO THE FUTURE better understanding of the immunological response system.
surfactant?
Woods: I have been trying to fit quite a few high Dk gas permeable lenses over the past few years. When I have patients in whom the lens will not wet in the eye, I have been sending the lenses back to the manufacturers and blaming them. What I found interesting was the comment that we should tell the patients to take those lenses away to let them settle down. How long should we leave those lenses in the eye to see if wettability is likely to improve? Is that for all gas permeable lenses, regardless of Dk, and at what level of Dk should we be thinking of doing that?
Question: Because wetting improves on the basis of absorption of certain tear constituents, and maybe the cleaner removes those and is acting in a negative fashion.
Holden: There are many, many things that affect the wettability of RGP lenses: how well they were manufactured, how well they were cleaned after manufacturing, whether all the grease and the oil was removed, and so on. When they come into the practice they probably need to be soaked for 48 hours to obtain full water content into the lenses, and then they are put into the eye; if they are not wetring too well, over a period of time they will wet. In terms of how long, I guess a couple of days usually shows adequate improvement to be able to judge. However, if something is badly wetting, it is not on anyway.
de Brabander: We have the same experience. It takes 1-3 days for a lens to become properly wet, and I do not think this depends very much on the Dk.
Tighe: This is a very rational period of time, which is explained by all the events we discussed earlier. It is not really Dk-related, except to the extent that Dk inevitably changes the hydrophobicity of the material. Holden: In some cases manufacturers are now surfacetreating lenses with plasma. Is that to clean the surface, or does it create chemical changes that help?
Tighe: It does create chemical changes. But any surface that is plasma-treated will decay. Its surface activity will change. Really, the extent to which this is a benefit will depend upon the age of the lens. Generally, if there is silicon in the lens, it has been shown that the silicon methyl groups present in all lenses are changed to SiO2 on the surface. Certainly, plasma treatment makes a lens more wettable. It will also clean the surface, but this is a secondary consideration.
Holden: Very subtle. Question: Or does the cleaner not take away these beneficial tear constituents? Tighe: Imagine cooking sausages in a flying pan and then leaving the pan overnight and coming next morning with cold water and some washing up liquid; one would never remove all that grease from the surface. Quantitatively, the surfactant cleaners only remove at best 60-70% of what is on and in the surface layers. It is essential to use the surfactant cleaner, but it will not remove all the material. It will not remove the material that is strongly bound to the lens, and that will be beneficial in conditioning the lens - to use the terms that were used earlier. Question: Would it not be better to use a separate wetting solution of higher viscosity, rather than all-in-one wetting-andsoaking solutions? de Brabander: Why should we? Holden: Is it better to use a specialised wetting solution? de Brabander: I do not think so: no. Tighe: They differ by quite a bit. I really do not think there is any case for choosing a single-purpose rather than a multipurpose solution. The surface tensions and wetting characteristics are not very different between all-in-one solutions and single-purpose solutions. The question of viscosity is more a matter of personal preference. I do not think there is any case for making a rule based on this physical measurement. Bosch: We were discussing the replacement rate of contact
Question: A quick corollary to what has been said. Should the patient not use their surfactant cleaner in the first 3-4 days of wearing their gas permeable lenses?
lenses. We know that with soft contact lenses the ideal rate of replacement is between half a year and perhaps a week. But now we are in the process of replacing RGP lenses. Surely it is our job as contact lens practitioners to prevent problems. We are talking about contact lens consumers and we should not wait for problems to appear, but should prevent this. In this light, annual replacement would be preferable to polishing and cleaning lenses, because cleaning and polishing really can screw up lenses.
Holden: Not in my estimation. Why would one not use a
de Brabander: I agree; if one can afford it.
SESSION II: CLINICAL MANAGEMENT AND VISION Panel: Joseph Molinari, Timothy Comstock, Neil Cox, and Ian Davies Discussion Mitchell: 'Experimental' contact lens research seems to have manufacturer bias. What is the best way to receive adequate funding for independent experimental contact lens research without running into this manufacturer bias?
Molinari: In private practice, one way is to persuade associations, such as the British Contact Lens Association (BCLA) to give a grant, and then there is no bias to a manufacturer. The
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Dallos Award is available and there are several associations that have monies available to do research projects. We have used Dallos money to study contact lenses in underwater environments. In the US, the federal government spends much money on esoteric studies. The American Optometric Association and the Academy of Optometry have put together a book that shows where to go to obtain these monies. There is money around.
SESSION II: CLINICAL MANAGEMENT AND VISION
Several of the studies that I have done, I piggybacked on studies I knew would be given to me by manufacturers. About 4 years ago I presented a paper on bifocal lenses, monovision, independent refractive bifocals, and dependent refractive bifocals. I piggybacked several clinical studies into that project, but this was very difficult. So, someone who is ingenious and who can motivate themselves to modify their environment as well as their private practice in these areas can do clinical studies on a shoestring or on a bootstrap. I would apply (in fact, I should like to apply again) for the Dallos Award to obtain another $3000. It provides seed money for any type of project, and the money is available every year. So, to answer the question, right here in your own association you have seed money to do any project, and once you get recognition from the BCLA you can take that and go to another company, or go to another organisation, and say you have the money to do this and how about some money to continue the project. That is what we did on the dive study.
Macalister: Could Mr Comstock elaborate on the sequence of different bifocal lenses tried in his flowchart? Are there any specific patient characteristics that would have him try a parficular lens first to avoid the tedious process of going through the whole lot?
Comstock: The flowchart that was used for the study was strictly based on the patient's add power; if the patient failed at monovision and had an add of less than 1.25D, an aspheric design lens was used, and if the add was greater than 1.25D, a translating bifocal lens was used. This was for the purpose of that study. In practice, there are patient characteristics that are examined closely in deciding which type of bifocal lens might be the most logical to use. I discussed these with the alternating lens. We look at lid characteristics, anatomy, tear volume, and such like. For the simultaneous vision aspheric multifocal, we want patients who have large pupils. There is a whole list of such criteria, but for the purpose of the study described, this was based strictly on add power.
Comstock: I can report what happened in this particular study. We did not control how the practitioners provided the lenses to their patients, so they could charge their patients full fees if they chose, or they could provide the lenses free. When I have more time to talk about this study I talk about some of these considerations and potential biases, and it can really be argued both ways. If the lenses are free, the argument can be made that the patients are more likely to accept something because they have not paid for it. On the other hand, if the lenses are offered for free, the argument can be made that the type of patient who will be attracted is the one who says, TI1 give it a go. What the heck? It will not cost me anything.' I think there is an effect on success rates, but I am not sure it is always one way or the other. Molinari: This has bothered me a lot because I do many of these studies. I think emphatically yes, there is an effect. But this is actually a temporal question: success rate over how long a period of time? Through to the end of the study? Usually people studied stay on for a while because they have the feeling they might become involved in another study somewhere down the line, and be given more free lenses. We have had people go through 10 years of our practice and never pay for any lenses. It is one of the problems we have in doing this type of study, and it is definitely a factor. ff anyone in the audience would like to argue the case I would be happy to argue it. To me as a clinician dealing in this environment, there is definitely an effect, but it is a function of the time factor after the study has ended. So many clinicians are nodding their heads, that I imagine they run into the same type of problem.
Papas: The pricing of lenses to study patients definitely has an effect on the outcome of the study, particularly if we are talking about a complicated bifocal lens that may cost a substanfial amount of money compared to a monovision alternative, which is relatively cheap. Given the choice, even if the performance is fairly similar, most people will go for the one that costs them less.
Macalister: How long did the patients wear each bifocal type
Ehrlich: Is there any correlation between the questions asked
before it was deemed a success or a failure?
for visual quality?
Comstock: One week - the patients were brought back at 1 week and the decision made as to whether to proceed to the end of the month, but at the end of the month they could have been switched to a new bifocal if they had not worn the lenses. The characteristic that we chose for success was 20 hours a week. If the patients decided after the week that they were not able to do that, they were classified as unsuccessful and moved on through the flowchart.
Davies: In other words, did we ask 'Is visual quality bad?' under certain circumstances, and the same for high and low contrast acuities? The questions were phrased in the same way and dealt with overall visual quality. No comment was made about any specific lighting conditions, work conditions, or anything of that kind; we requested a general overall perception.
Molinari: The Gulf War was the first time that contact lenses Papas: How long were Mr Cox's lenses allowed to settle? Cox: We used several base curves and most lenses were left to settle for 15 minutes. I take the point. We have between three and five base curves, particularly for our test lens, to ensure that the lens fit was not contributing to the result. Papas: I was wondering whether corneal oedema might contribute to the forward scattering.
Cox: I do not think the lenses were in long enough for that. Each series of 10 recordings probably took 2-5 minutes, depending on how alert the patient was, and we could probably screen oedema out fairly safely. I do not think silver nitrate affects the oxygen permeability of the lens. LIoyck Is there a tendency for the manufacturer-controlled clinical trials to report a higher-than-actual success rate due to the supply of free product to the patient?
were used in combat operations. I do not know if that is a known fact. I was involved with designing the protocol for some of the personnel from our bases. We ran into some who had a problem with visual acuity. They had toric lenses and kept complaining that their vision was not good enough for what they wanted to do. Every time we measured them, we found their vision to be adequate, like 20/20, 20/25; it fulfilled the criteria that we wanted. We have to start investigating this within this next year. What kind of variables are we dealing with? Are the lenses rotating and at certain times they do not see and so are complaining about the fact that they cannot see because of the rotation? Or is it something else?
Davies: It is one of those multifactorial things. I would imagine it is extremely difficult to come up with any one single reason. Certainly rotation plays a part. Magnification or minification of the retinal image also plays a part, as does the binocular summation of the two eyes. This is why it is so
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SESSIONII: CLINICALMANAGEMENTANDVISION difficult to tie things down. Following on from that, there are people whose visual acuity on each occasion they come in is all right, but they do not perceive it as being so. If we are evaluating a lens or any refractive correction, we have to take personal perception into consideration, as well as the objective measurements that we can take. Bosch: Would it be an idea to use the visual analogue scales horizontally, as opposed to vertically? Davies: One of the difficulties with using the scale horizontally is that those who are right-handed mark on one side and those who are left-handed tend to mark on the other side. With a vertical scale that is one bias that theoretically is removed. This problem could be overcome by having two visual analogue scales, marking one above the other and taking the average. Mitchell: Did Mr Davies use parametric or non-parametric statistics? Davies: Most of the literature suggests that the use of visual analogue scales and interval scales cannot be considered to be normal data. In fact, we used non-parametric statistics. Having said that, on a more intuitive basis, if the distribution of the data looked normal, then just for the sake of it we considered it to be so and did normal statistics as well; we came up with the same result. This is a fairly pragmatic approach. Mitchell'. I have used a stray-light meter and have found an increase in glare in contact lens wearers. Why is it 7.5Hz for the stray-light source?
report tremendous problems with glare, but when we examine them with the slit-lamp they do not flinch at all; we wonder whether this is a functional anomaly or whether they really have a problem. One aspect we want to look at is spectacle-mounted tints, and to look at this factor in isolation from the contact lens, because t h e tint is part of the system that we have been examining. The brief answer to the question is that it may be quite a valuable tool. Patek In the light of Mr Cox's finding, how would he manage those aniridic patients whose problem is one of glare and not cosmesis with contact lenses? Cox: How would we select an appropriate contact lens? If the patient is not bothered about cosmesis then a darkly tinted translucent lens will reduce symptoms of glare. When I see a patient for the first time, my approach is to try and identify the primary complaint. No doubt some weight is put towards cosmesis, but at the initial visit the patient may say that the main problem is glare; we say fine and fit this sort of lens. And then, fairly typically, the patient returns a couple of months later and says that we have removed the glare, but that the state of the eye is drawing attention from other people. It is very difficult to look at one factor in isolation. Inevitably, there is a compromise. But the way to manage these patients is to explain to them what the compromise is, what the plus points are, and what the minus points are; this helps a lot. Harris: Given present concerns regarding hypoxia and the trend for higher Dk materials, are manufacturers producing bifocals from adequate materials?
Cox: I regret I do not know. Rumney: Would Mr Cox like to speculate which contact lens method of reducing glare is most likely to reduce disability and which discomfort? Cox: I am not sure how I am to differentiate between disability and discomfort glare. There is little doubt, both on an empirical basis and from our preliminary findings, that translucent tinted lenses are more likely to reduce glare than most other lenses, but they are not necessarily the most cosmetically attractive. When we prescribe lenses to these patients we have to examine all the factors; some people's primary motivation towards contact lens wear is to enhance their cosmetic appearance. Rumney: In dealing with patients who run into problems with glare, it is very important to define what their particular problem is. It can be defined in terms of discussions with them as to whether it is a problem of discomfort glare or disability glare. It is also possible to measure whether it is disability or discomfort glare that is affecting their vision. My speculation is that in this case it is predominantly disability glare, but some contact lens wearers do not run into disability glare but discomfort glare. These are two clearly defined separate issues, which is why I asked Mr Cox to speculate how to differentiate between the two. Cox: It may be a matter of semantics, but we hope we have a useful tool for predicting which contact lenses may help patients who present in our clinics. Bailey: Could the luminance equipment be used to determine whether patients really require sun spectacles, and if so, what lens light transmission would be best? Cox: It probably could. I am sure we have all had patients that
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Comstock: Certainly, if we can produce these optical designs in higher Dk materials, that would be to the benefit of the practitioner and also the manufacturer. I am not a materials scientist, but I do know that some materials are much easier to work with than others and so making the complicated designs that some of the bifocal lenses have is sometimes an impossible task in the higher Dk materials. It is, however, something that we are always looking to do, to produce the same designs in higher Dk materials. Is it irresponsible to sell them in the lower Dk materials? It is not irresponsible as long as no one misrepresents what it is they are providing. Cox: That is technology driven. There is an obvious desire for high Dk bifocal lenses, but also for toric lenses - more so for toric lenses. At the moment the limiting factor appears to be reproducibility of particular high water content materials when making more complicated designs. Davies: For presbyopic correction, dealing with the ageing cornea, if we have already established that we should be fitring high Dk single-vision lenses, then we should fit high Dk bifocal lenses. The same applies to hydrogel materials. We are all warm towards higher water content materials improving transmissibility, and yet the majority of lenses that are available to us are in low water content materials. So there is considerable room for improvement. Leslie: Would the members of the panel prescribe spectacles for monovision prescriptions, i.e. to be worn for driving on top of the lenses that they are wearing for monovision? Comstock: Personally, I do not because the spectacles would be limited to that use only. I prescribe a third lens that can be worn for driving if the monovision is irritating. If the high contrast situation that the
SESSIONII: CLINICALMANAGEMENTANDVISION patients are put into when they are driving causes a problem or breakdown in that suppression, then we either advise that they do not wear lenses when they drive and simply wear spectacles, or we prescribe a third contact lens. Most of our monovision patients are in disposable or plan replacement modalities, which makes it easier to do that.
Cox: This is a wonderful vision of someone having a pair of reading glasses, a pair of distance glasses, monovision, with a spare lens either way, whether for distance or reading, and a couple of pairs of spectacles over the top. To be practical, if that is the only way that someone can
manage monovision and that individual is prepared to do it, then why not? But the reality is that this will not happen very often.
Davies: Very rarely, but I am aware of litigation in the US where practitioners have been liable for not pointing out the visual compromise in monovision where road traffic accidents have occurred. So it is an important issue to be brought up early when fitting people with monovision.
Molinari: I side with Mr Comstock. It must be the American in me to give them another lens. I do not see the option of giving the person another pair of glasses.
SESSION III: THE COMPROMISED CORNEAL ENVIRONMENT Panel: Peter Scanlon, John Dart, Cherry Radford, Sudi Patel, and William J. Benjamin
Discussion
Ivins: Did the patients in the extended wear soft contact lens group have a similar Rx distribution to the rigid gas permeable contact lens group or did it include many aphakic patients?
Pate# What proportion of contact lens wearers in John Dart's study were elderly aphakic patients?
Question: Why are risks greater in extended wear aphakic patients than in cosmetic extended wear patients? Dart: There were no extended wear aphakic patients in our study, but we have done such studies in the past. The figures I was quoting were entirely based on cosmetic patients, i.e. patients who had low myopia and low hypermetropia. We excluded the aphakic patients because, as the question implies, the risks for all complications have been shown to be much higher for aphakic lens users. It is hard to extrapolate from aphakic lens users to patients who use lenses for low refractive errors. The eye is different it has a reduced corneal sensation. The corneal metabolism, possibly as a result of that, is different, and the response to the metabolic stress of lens wear may be quite different from that in a cosmetic user. So we cannot extrapolate from one to the other. On top of that, aphakic contact lenses have very thick optical centres and consequently greatly reduced transmission. It may be that the high risk in aphakic extended wearers is telling us something about the effect of the metabolic compromise introduced by lens wear on these different complications, but we cannot assume that because the eye is different in the first place. So I do not think the two are comparable. But, undoubtedly, aphakic extended wear, and aphakic daily wear probably, does carry greater risk for all complications. That has been shown for extended wear and it may be due to the factors that I have outlined.
ago and it was noted that after the extra stress of cataract surgery, when endothelial cells are inevitably lost, patients who had been long-term lens wearers were possibly at greater risk of developing bullous keratopathy. But no-one had shown that polymegethism itself affected the function or resulted in reduced numbers of endothelial cells. Until now I felt that, although patients suffer polymegethism, which shows that something is happening, there was really no evidence to show that this would be likely to cause any problems, because the function of those polymegethic cells was probably normal. However, this year Scott Macrae, who is a good worker and has published some previous work on polymegethism, presented a group of hard lens wearers who have been using contact lenses for 20 or more years, in whom there were reduced cell counts with gross polymegethism. It remains to be seen whether that work is substantiated by work done elsewhere, but it is the first wellsubstantiated suggestion that polymegethism may lead to a compromise in endothelial function. And we need to be aware of that. It may not be a problem in the future even if he is proved to be correct. It may not be a problem with the new high Dk materials that are being used.
Pursey: Although Mrs Radford has indicated a much greater compliance with chlorine disinfecting systems, what about the fact that inadequate removal of the surfactants may render the chlorine disinfectant ineffective? Perhaps peroxide systems, even if not used entirely as instructed, are still a safer disinfectant.
Radford: We did look at the rinsing of surfactant and, indeed, whether the surfactant was used on lens removal or in the morning before insertion; nevertheless, the chlorine-based disinfection system users did come out more compliant. All disinfection systems are partly inactivated by organic debris.
Patel: What are the long-term implications of polymegethism?
Question: What would be the recommended way to clean contact lens cases?
Dart: That is an interesting question. Until this year I would
Radford: More research needs to be directed at case cleaning
have said probably none, in that there had been a suggestion that patients who were long-term contact lens wearers might be slightly at risk, or more at risk, of developing corneal oedema after cataract surgery. This was published 2-3 years
techniques and the frequency of case replacement. In the study I recommend friction rinsing and air drying. Patients who did this or similar were classified as compliant for case cleaning.
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surfactant?
Woods: I have been trying to fit quite a few high Dk gas permeable lenses over the past few years. When I have patients in whom the lens will not wet in the eye, I have been sending the lenses back to the manufacturers and blaming them. What I found interesting was the comment that we should tell the patients to take those lenses away to let them settle down. How long should we leave those lenses in the eye to see if wettability is likely to improve? Is that for all gas permeable lenses, regardless of Dk, and at what level of Dk should we be thinking of doing that?
Question: Because wetting improves on the basis of absorption of certain tear constituents, and maybe the cleaner removes those and is acting in a negative fashion.
Holden: There are many, many things that affect the wettability of RGP lenses: how well they were manufactured, how well they were cleaned after manufacturing, whether all the grease and the oil was removed, and so on. When they come into the practice they probably need to be soaked for 48 hours to obtain full water content into the lenses, and then they are put into the eye; if they are not wetring too well, over a period of time they will wet. In terms of how long, I guess a couple of days usually shows adequate improvement to be able to judge. However, if something is badly wetting, it is not on anyway.
de Brabander: We have the same experience. It takes 1-3 days for a lens to become properly wet, and I do not think this depends very much on the Dk.
Tighe: This is a very rational period of time, which is explained by all the events we discussed earlier. It is not really Dk-related, except to the extent that Dk inevitably changes the hydrophobicity of the material. Holden: In some cases manufacturers are now surfacetreating lenses with plasma. Is that to clean the surface, or does it create chemical changes that help?
Tighe: It does create chemical changes. But any surface that is plasma-treated will decay. Its surface activity will change. Really, the extent to which this is a benefit will depend upon the age of the lens. Generally, if there is silicon in the lens, it has been shown that the silicon methyl groups present in all lenses are changed to SiO2 on the surface. Certainly, plasma treatment makes a lens more wettable. It will also clean the surface, but this is a secondary consideration.
Holden: Very subtle. Question: Or does the cleaner not take away these beneficial tear constituents? Tighe: Imagine cooking sausages in a flying pan and then leaving the pan overnight and coming next morning with cold water and some washing up liquid; one would never remove all that grease from the surface. Quantitatively, the surfactant cleaners only remove at best 60-70% of what is on and in the surface layers. It is essential to use the surfactant cleaner, but it will not remove all the material. It will not remove the material that is strongly bound to the lens, and that will be beneficial in conditioning the lens - to use the terms that were used earlier. Question: Would it not be better to use a separate wetting solution of higher viscosity, rather than all-in-one wetting-andsoaking solutions? de Brabander: Why should we? Holden: Is it better to use a specialised wetting solution? de Brabander: I do not think so: no. Tighe: They differ by quite a bit. I really do not think there is any case for choosing a single-purpose rather than a multipurpose solution. The surface tensions and wetting characteristics are not very different between all-in-one solutions and single-purpose solutions. The question of viscosity is more a matter of personal preference. I do not think there is any case for making a rule based on this physical measurement. Bosch: We were discussing the replacement rate of contact
Question: A quick corollary to what has been said. Should the patient not use their surfactant cleaner in the first 3-4 days of wearing their gas permeable lenses?
lenses. We know that with soft contact lenses the ideal rate of replacement is between half a year and perhaps a week. But now we are in the process of replacing RGP lenses. Surely it is our job as contact lens practitioners to prevent problems. We are talking about contact lens consumers and we should not wait for problems to appear, but should prevent this. In this light, annual replacement would be preferable to polishing and cleaning lenses, because cleaning and polishing really can screw up lenses.
Holden: Not in my estimation. Why would one not use a
de Brabander: I agree; if one can afford it.
SESSION II: CLINICAL MANAGEMENT AND VISION Panel: Joseph Molinari, Timothy Comstock, Neil Cox, and Ian Davies Discussion Mitchell: 'Experimental' contact lens research seems to have manufacturer bias. What is the best way to receive adequate funding for independent experimental contact lens research without running into this manufacturer bias?
Molinari: In private practice, one way is to persuade associations, such as the British Contact Lens Association (BCLA) to give a grant, and then there is no bias to a manufacturer. The
184
Dallos Award is available and there are several associations that have monies available to do research projects. We have used Dallos money to study contact lenses in underwater environments. In the US, the federal government spends much money on esoteric studies. The American Optometric Association and the Academy of Optometry have put together a book that shows where to go to obtain these monies. There is money around.
SESSION II: CLINICAL MANAGEMENT AND VISION
Several of the studies that I have done, I piggybacked on studies I knew would be given to me by manufacturers. About 4 years ago I presented a paper on bifocal lenses, monovision, independent refractive bifocals, and dependent refractive bifocals. I piggybacked several clinical studies into that project, but this was very difficult. So, someone who is ingenious and who can motivate themselves to modify their environment as well as their private practice in these areas can do clinical studies on a shoestring or on a bootstrap. I would apply (in fact, I should like to apply again) for the Dallos Award to obtain another $3000. It provides seed money for any type of project, and the money is available every year. So, to answer the question, right here in your own association you have seed money to do any project, and once you get recognition from the BCLA you can take that and go to another company, or go to another organisation, and say you have the money to do this and how about some money to continue the project. That is what we did on the dive study.
Macalister: Could Mr Comstock elaborate on the sequence of different bifocal lenses tried in his flowchart? Are there any specific patient characteristics that would have him try a parficular lens first to avoid the tedious process of going through the whole lot?
Comstock: The flowchart that was used for the study was strictly based on the patient's add power; if the patient failed at monovision and had an add of less than 1.25D, an aspheric design lens was used, and if the add was greater than 1.25D, a translating bifocal lens was used. This was for the purpose of that study. In practice, there are patient characteristics that are examined closely in deciding which type of bifocal lens might be the most logical to use. I discussed these with the alternating lens. We look at lid characteristics, anatomy, tear volume, and such like. For the simultaneous vision aspheric multifocal, we want patients who have large pupils. There is a whole list of such criteria, but for the purpose of the study described, this was based strictly on add power.
Comstock: I can report what happened in this particular study. We did not control how the practitioners provided the lenses to their patients, so they could charge their patients full fees if they chose, or they could provide the lenses free. When I have more time to talk about this study I talk about some of these considerations and potential biases, and it can really be argued both ways. If the lenses are free, the argument can be made that the patients are more likely to accept something because they have not paid for it. On the other hand, if the lenses are offered for free, the argument can be made that the type of patient who will be attracted is the one who says, TI1 give it a go. What the heck? It will not cost me anything.' I think there is an effect on success rates, but I am not sure it is always one way or the other. Molinari: This has bothered me a lot because I do many of these studies. I think emphatically yes, there is an effect. But this is actually a temporal question: success rate over how long a period of time? Through to the end of the study? Usually people studied stay on for a while because they have the feeling they might become involved in another study somewhere down the line, and be given more free lenses. We have had people go through 10 years of our practice and never pay for any lenses. It is one of the problems we have in doing this type of study, and it is definitely a factor. ff anyone in the audience would like to argue the case I would be happy to argue it. To me as a clinician dealing in this environment, there is definitely an effect, but it is a function of the time factor after the study has ended. So many clinicians are nodding their heads, that I imagine they run into the same type of problem.
Papas: The pricing of lenses to study patients definitely has an effect on the outcome of the study, particularly if we are talking about a complicated bifocal lens that may cost a substanfial amount of money compared to a monovision alternative, which is relatively cheap. Given the choice, even if the performance is fairly similar, most people will go for the one that costs them less.
Macalister: How long did the patients wear each bifocal type
Ehrlich: Is there any correlation between the questions asked
before it was deemed a success or a failure?
for visual quality?
Comstock: One week - the patients were brought back at 1 week and the decision made as to whether to proceed to the end of the month, but at the end of the month they could have been switched to a new bifocal if they had not worn the lenses. The characteristic that we chose for success was 20 hours a week. If the patients decided after the week that they were not able to do that, they were classified as unsuccessful and moved on through the flowchart.
Davies: In other words, did we ask 'Is visual quality bad?' under certain circumstances, and the same for high and low contrast acuities? The questions were phrased in the same way and dealt with overall visual quality. No comment was made about any specific lighting conditions, work conditions, or anything of that kind; we requested a general overall perception.
Molinari: The Gulf War was the first time that contact lenses Papas: How long were Mr Cox's lenses allowed to settle? Cox: We used several base curves and most lenses were left to settle for 15 minutes. I take the point. We have between three and five base curves, particularly for our test lens, to ensure that the lens fit was not contributing to the result. Papas: I was wondering whether corneal oedema might contribute to the forward scattering.
Cox: I do not think the lenses were in long enough for that. Each series of 10 recordings probably took 2-5 minutes, depending on how alert the patient was, and we could probably screen oedema out fairly safely. I do not think silver nitrate affects the oxygen permeability of the lens. LIoyck Is there a tendency for the manufacturer-controlled clinical trials to report a higher-than-actual success rate due to the supply of free product to the patient?
were used in combat operations. I do not know if that is a known fact. I was involved with designing the protocol for some of the personnel from our bases. We ran into some who had a problem with visual acuity. They had toric lenses and kept complaining that their vision was not good enough for what they wanted to do. Every time we measured them, we found their vision to be adequate, like 20/20, 20/25; it fulfilled the criteria that we wanted. We have to start investigating this within this next year. What kind of variables are we dealing with? Are the lenses rotating and at certain times they do not see and so are complaining about the fact that they cannot see because of the rotation? Or is it something else?
Davies: It is one of those multifactorial things. I would imagine it is extremely difficult to come up with any one single reason. Certainly rotation plays a part. Magnification or minification of the retinal image also plays a part, as does the binocular summation of the two eyes. This is why it is so
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SESSIONII: CLINICALMANAGEMENTANDVISION difficult to tie things down. Following on from that, there are people whose visual acuity on each occasion they come in is all right, but they do not perceive it as being so. If we are evaluating a lens or any refractive correction, we have to take personal perception into consideration, as well as the objective measurements that we can take. Bosch: Would it be an idea to use the visual analogue scales horizontally, as opposed to vertically? Davies: One of the difficulties with using the scale horizontally is that those who are right-handed mark on one side and those who are left-handed tend to mark on the other side. With a vertical scale that is one bias that theoretically is removed. This problem could be overcome by having two visual analogue scales, marking one above the other and taking the average. Mitchell: Did Mr Davies use parametric or non-parametric statistics? Davies: Most of the literature suggests that the use of visual analogue scales and interval scales cannot be considered to be normal data. In fact, we used non-parametric statistics. Having said that, on a more intuitive basis, if the distribution of the data looked normal, then just for the sake of it we considered it to be so and did normal statistics as well; we came up with the same result. This is a fairly pragmatic approach. Mitchell'. I have used a stray-light meter and have found an increase in glare in contact lens wearers. Why is it 7.5Hz for the stray-light source?
report tremendous problems with glare, but when we examine them with the slit-lamp they do not flinch at all; we wonder whether this is a functional anomaly or whether they really have a problem. One aspect we want to look at is spectacle-mounted tints, and to look at this factor in isolation from the contact lens, because t h e tint is part of the system that we have been examining. The brief answer to the question is that it may be quite a valuable tool. Patek In the light of Mr Cox's finding, how would he manage those aniridic patients whose problem is one of glare and not cosmesis with contact lenses? Cox: How would we select an appropriate contact lens? If the patient is not bothered about cosmesis then a darkly tinted translucent lens will reduce symptoms of glare. When I see a patient for the first time, my approach is to try and identify the primary complaint. No doubt some weight is put towards cosmesis, but at the initial visit the patient may say that the main problem is glare; we say fine and fit this sort of lens. And then, fairly typically, the patient returns a couple of months later and says that we have removed the glare, but that the state of the eye is drawing attention from other people. It is very difficult to look at one factor in isolation. Inevitably, there is a compromise. But the way to manage these patients is to explain to them what the compromise is, what the plus points are, and what the minus points are; this helps a lot. Harris: Given present concerns regarding hypoxia and the trend for higher Dk materials, are manufacturers producing bifocals from adequate materials?
Cox: I regret I do not know. Rumney: Would Mr Cox like to speculate which contact lens method of reducing glare is most likely to reduce disability and which discomfort? Cox: I am not sure how I am to differentiate between disability and discomfort glare. There is little doubt, both on an empirical basis and from our preliminary findings, that translucent tinted lenses are more likely to reduce glare than most other lenses, but they are not necessarily the most cosmetically attractive. When we prescribe lenses to these patients we have to examine all the factors; some people's primary motivation towards contact lens wear is to enhance their cosmetic appearance. Rumney: In dealing with patients who run into problems with glare, it is very important to define what their particular problem is. It can be defined in terms of discussions with them as to whether it is a problem of discomfort glare or disability glare. It is also possible to measure whether it is disability or discomfort glare that is affecting their vision. My speculation is that in this case it is predominantly disability glare, but some contact lens wearers do not run into disability glare but discomfort glare. These are two clearly defined separate issues, which is why I asked Mr Cox to speculate how to differentiate between the two. Cox: It may be a matter of semantics, but we hope we have a useful tool for predicting which contact lenses may help patients who present in our clinics. Bailey: Could the luminance equipment be used to determine whether patients really require sun spectacles, and if so, what lens light transmission would be best? Cox: It probably could. I am sure we have all had patients that
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Comstock: Certainly, if we can produce these optical designs in higher Dk materials, that would be to the benefit of the practitioner and also the manufacturer. I am not a materials scientist, but I do know that some materials are much easier to work with than others and so making the complicated designs that some of the bifocal lenses have is sometimes an impossible task in the higher Dk materials. It is, however, something that we are always looking to do, to produce the same designs in higher Dk materials. Is it irresponsible to sell them in the lower Dk materials? It is not irresponsible as long as no one misrepresents what it is they are providing. Cox: That is technology driven. There is an obvious desire for high Dk bifocal lenses, but also for toric lenses - more so for toric lenses. At the moment the limiting factor appears to be reproducibility of particular high water content materials when making more complicated designs. Davies: For presbyopic correction, dealing with the ageing cornea, if we have already established that we should be fitring high Dk single-vision lenses, then we should fit high Dk bifocal lenses. The same applies to hydrogel materials. We are all warm towards higher water content materials improving transmissibility, and yet the majority of lenses that are available to us are in low water content materials. So there is considerable room for improvement. Leslie: Would the members of the panel prescribe spectacles for monovision prescriptions, i.e. to be worn for driving on top of the lenses that they are wearing for monovision? Comstock: Personally, I do not because the spectacles would be limited to that use only. I prescribe a third lens that can be worn for driving if the monovision is irritating. If the high contrast situation that the
SESSIONII: CLINICALMANAGEMENTANDVISION patients are put into when they are driving causes a problem or breakdown in that suppression, then we either advise that they do not wear lenses when they drive and simply wear spectacles, or we prescribe a third contact lens. Most of our monovision patients are in disposable or plan replacement modalities, which makes it easier to do that.
Cox: This is a wonderful vision of someone having a pair of reading glasses, a pair of distance glasses, monovision, with a spare lens either way, whether for distance or reading, and a couple of pairs of spectacles over the top. To be practical, if that is the only way that someone can
manage monovision and that individual is prepared to do it, then why not? But the reality is that this will not happen very often.
Davies: Very rarely, but I am aware of litigation in the US where practitioners have been liable for not pointing out the visual compromise in monovision where road traffic accidents have occurred. So it is an important issue to be brought up early when fitting people with monovision.
Molinari: I side with Mr Comstock. It must be the American in me to give them another lens. I do not see the option of giving the person another pair of glasses.
SESSION III: THE COMPROMISED CORNEAL ENVIRONMENT Panel: Peter Scanlon, John Dart, Cherry Radford, Sudi Patel, and William J. Benjamin
Discussion
Ivins: Did the patients in the extended wear soft contact lens group have a similar Rx distribution to the rigid gas permeable contact lens group or did it include many aphakic patients?
Pate# What proportion of contact lens wearers in John Dart's study were elderly aphakic patients?
Question: Why are risks greater in extended wear aphakic patients than in cosmetic extended wear patients? Dart: There were no extended wear aphakic patients in our study, but we have done such studies in the past. The figures I was quoting were entirely based on cosmetic patients, i.e. patients who had low myopia and low hypermetropia. We excluded the aphakic patients because, as the question implies, the risks for all complications have been shown to be much higher for aphakic lens users. It is hard to extrapolate from aphakic lens users to patients who use lenses for low refractive errors. The eye is different it has a reduced corneal sensation. The corneal metabolism, possibly as a result of that, is different, and the response to the metabolic stress of lens wear may be quite different from that in a cosmetic user. So we cannot extrapolate from one to the other. On top of that, aphakic contact lenses have very thick optical centres and consequently greatly reduced transmission. It may be that the high risk in aphakic extended wearers is telling us something about the effect of the metabolic compromise introduced by lens wear on these different complications, but we cannot assume that because the eye is different in the first place. So I do not think the two are comparable. But, undoubtedly, aphakic extended wear, and aphakic daily wear probably, does carry greater risk for all complications. That has been shown for extended wear and it may be due to the factors that I have outlined.
ago and it was noted that after the extra stress of cataract surgery, when endothelial cells are inevitably lost, patients who had been long-term lens wearers were possibly at greater risk of developing bullous keratopathy. But no-one had shown that polymegethism itself affected the function or resulted in reduced numbers of endothelial cells. Until now I felt that, although patients suffer polymegethism, which shows that something is happening, there was really no evidence to show that this would be likely to cause any problems, because the function of those polymegethic cells was probably normal. However, this year Scott Macrae, who is a good worker and has published some previous work on polymegethism, presented a group of hard lens wearers who have been using contact lenses for 20 or more years, in whom there were reduced cell counts with gross polymegethism. It remains to be seen whether that work is substantiated by work done elsewhere, but it is the first wellsubstantiated suggestion that polymegethism may lead to a compromise in endothelial function. And we need to be aware of that. It may not be a problem in the future even if he is proved to be correct. It may not be a problem with the new high Dk materials that are being used.
Pursey: Although Mrs Radford has indicated a much greater compliance with chlorine disinfecting systems, what about the fact that inadequate removal of the surfactants may render the chlorine disinfectant ineffective? Perhaps peroxide systems, even if not used entirely as instructed, are still a safer disinfectant.
Radford: We did look at the rinsing of surfactant and, indeed, whether the surfactant was used on lens removal or in the morning before insertion; nevertheless, the chlorine-based disinfection system users did come out more compliant. All disinfection systems are partly inactivated by organic debris.
Patel: What are the long-term implications of polymegethism?
Question: What would be the recommended way to clean contact lens cases?
Dart: That is an interesting question. Until this year I would
Radford: More research needs to be directed at case cleaning
have said probably none, in that there had been a suggestion that patients who were long-term contact lens wearers might be slightly at risk, or more at risk, of developing corneal oedema after cataract surgery. This was published 2-3 years
techniques and the frequency of case replacement. In the study I recommend friction rinsing and air drying. Patients who did this or similar were classified as compliant for case cleaning.
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