UK Keratoconus Self Help and Support Association
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Thank you for inviting me to this remarkable convention. I'm really stunned by the turnout and congratulate you all!
My talk is intended to address a misunderstanding that I find among some of my colleagues in this country - that is, that keratoconus is predominantly a surgical condition. Most ophthalmologists are first and foremost eye surgeons and surgeons operate. Because there is this conception that KC is a condition requiring surgery, I want to redress the balance and present reasons why it may not be. In saying that, I'm fully aware that there are members of this audience who have undergone surgery, in some cases by myself. There is a case for surgery and sometimes it is the only possible means of management. But in the absence of a national policy for KC, which we do not have and which I think we should have (and even better a European or global policy), surgeons tend to find their own way and, depending on the support they get from their optometrist colleagues, the results can be very different. I'm quite sure that if a person with KC were to present to a number of different ophthalmic surgeons the result would not be unanimous. Someone can come to me in Wimpole St and be told by me that they do not need surgery and can walk a few yards up the street and be told by someone else that they do. So I would like to present a rather pessimistic view of surgery, even though I am a surgeon and do carry out surgery - a paradox, maybe, but one that needs stating.
A brief history of corneal transplantation:
|1873||first corneal transplant from one gazelle to another.|
|1886||first successful human transplant - this was a lamellar transplant ie partial thickness, not full thickness.|
|1906||the first successful full thickness transplant.|
|1930||a paper was published reviewing 176 transplants and proudly announcing a 20% success rate By 1937 a 58% success rate being reported, while another surgeon not long after reported a 90% success in so-called 'suitable' cases. So up to the end of World War II there was an increasing success with transplants.|
We now understand corneal anatomy and physiology, we understand the so-called allograft reaction ie rejection. We can supply suitable corneal material, use micro-surgical techniques, and have various therapeutic drugs which allow us to prevent rejection to a large extent.
Our understanding of anatomy and physiology came about partly with the development of the specular microscope and a number of you will have had this examination. This enabled us for the first time to look at the living endothelium, which is the back layer of the cornea, and the shape and density of individual cells. There have been many experiments done on animal corneas on the effects of various drugs on this all important layer which keeps the cornea clear. The tissue in this layer of the cornea, the endothelium, is what is most likely to be damaged in classical transplant rejection. We now understand the role of T-lymphocytes and the so-called Langerhans cells in the causation of endothelial rejection. It used to be thought that the cornea was 'privileged' because it has no blood supply and therefore would not reject. This theory has now been replaced with the idea of 'tolerance' - the body is aware of a foreign tissue but chooses not to do anything about it. A state of immune tolerance then - a sort of equilibrium between foreign material and the recipient.
I mentioned the supply of donor tissue has improved. We now have eye banks and different means of corneal storage. The simplest is the whole eye kept refrigerated at 4°C, then there's tissue culture storage which involves a disc of cornea and sclera again preserved at 4°C in the fridge and also organ culture, which is done at blood temperature. The UK Transplant Service Eye Bank in Bristol with branches in Manchester and elsewhere uses organ culture and the great advantage of that is that one has up to a month to organise the operation. (The other methods are much more short term). Thanks to organ culture we can now carry out matched corneal procedures, because we have time in that month to carry out the necessary matching and seek out the appropriate recipient for that particular material.
Microsurgical techniques have improved because we have tiny little instruments which are quite beautiful and made specially for the purpose, we have better materials for suturing and the needles are lovely too. We have drugs - we can prevent infection with antibiotics and control inflammation with steroids and can suppress the immune response with a variety of drugs. The achievements of corneal transplants are the culmination of all that I've just outlined.
The remaining shortcomings are principally two - astigmatism and transplant rejection. There are also the complications of steroid use which are well known and the complications of immuno-suppression which are much less well familiar. So I'd like to talk principally about astigmatism and transplant rejection and then make a few comments about alternative methods of managing keratoconus. Astigmatism means that the cornea is steeper in one meridian than in another. The cornea might typically have a steep axis and a flat axis; they would usually be at right angles and that would be called regular astigmatism. Astigmatism is a very common condition in perfectly normal people with normal sight, but of course it becomes more of an issue when the cornea is abnormal or when it has been replaced.
Irregular corneal astigmatism is when the axes are not at right angles and the significance of that is that you can't correct the vision with glasses, you need something else such as a contact lens to do it. An unfortunate effect of irregular astigmatism is to change certain aspects of vision - it may affect the ability of the eye to see at low light levels, and it may mean that glare is a problem, even though the actual acuity, the sharpness of vision, may be normal.
Various factors cause astigmatism to result from a corneal transplant which can be divided into pre-surgical, surgical and post-surgical.
What do you do if you've got it? There are various ways in which we can correct astigmatism. I've mentioned glasses and contact lenses, and there is also refractive surgery to reduce astigmatism. This can be done with a variety of techniques including relaxing incision, compressive sutures or the excimer laser (which is more familiar to you as something which people pay to have done to lose their short sight - a quite different procedure).
It is very important to specify when we do an operation on a patient with KC that the chances are the patient will need to wear contact lenses afterwards. There is a great tendency for both doctors and nurses to imply to the patient that an operation is the way out of troublesome lens wear - that is not so. 50% to 60% of patients will need to wear contact lenses after a transplant. So if the operation is being done to obviate the need for contact lenses that is the wrong premise, and not a good reason. This is something that's not said often enough and that leads to misunderstandings.
Contact lens fitting after corneal surgery may be difficult. It's important that we recognise this, because the shape of the eye is now, well, not normal! It wasn't normal before, and it's certainly not normal after a corneal transplant - just abnormal in a different way!
Very often you'll have a flat centre and a steep periphery, so may need unusual lens shapes, which may need to be trapezoidal, may need to be large, may need to be scleral. We have in the past used hybrid lenses which are both soft and hard (hard in the middle and soft on the periphery). In other words, we have to pull out the whole contact lens inventory, all kinds of lenses, invent lenses, design lenses for individuals in order to fit successfully after a corneal transplant.
Another thing we have to remember is that the transplant is insensitive. It may take 5 or 10 years for the sensation to return to the cornea after transplantation, simply because nerves grow so slowly. It will come back in most cases, but it takes a long time and we have to bear in mind that fitting an insensitive cornea with a contact lens is potentially hazardous. Also we have to remember that the transplant's endothelial reserves may have been damaged in the course of the operation and we have to be sure to do nothing to compromise its survival.
The other thing that is less agreeable to talk about is rejection. A large study in Australia appeared 6 years ago - their rate of survival was 91% at 1 year falling to 69% at 7 years. (But this includes transplants done for variety of reasons - survival after operations done for KC tends to be much better than average). This study was of a heterogenous group which included both high and low risk patients. We've been aware for some time that the risk of rejection depends very much on whether the host cornea has blood vessels in it. A low risk patient would be one with no blood vessels. A study from S. Africa showed that a previous operation is not a risk factor in itself - the degree of neovascularisation (the growth of new blood vessels) is what constitutes the risk. That is easy to observe, so we can easily put patients into low, medium and high risk categories.
What can we do if a patient is a high risk group? We can choose to use matched tissue, as I mentioned earlier, although globally the value of matched tissue is still disputed. We tend to believe in it in Europe while in US they tend not to do so. Because the supply of matched tissue is unpredictable (details go into a computer) it is then impossible to state when the operation will take place - could be 3 wks or 3 yrs.
We do also thankfully have the possibility of immuno-suppression which is much safer than it ever was before thanks to a drug called Cyclosporin and other drugs that have been developed since. However this does have side effects which can be serious and treatment has to continue for at least a year.
Alternatives to normal (full thickness) transplantation include a lamellar (partial thickness) operation, something called epikeroplasty and other surgical procedures. A lamellar transplant is actually more difficult to do, takes longer, it's perfectly possible but just more difficult. It can lead to opacities between the transplant and the recipient cornea which can affect the vision quite a lot. If there is deep scarring in the recipient, it will remain after the operation and the visual function is then often disappointing. However, the all-important endothelial layer is left intact and so rejection is much less of a problem.
Epikeratoplasty was a few years ago trumpeted as a solution to the problem of KC - the 'living contact lens' which was sewn permanently to the eye. We machined a contact lens out of a piece of donor cornea and made a circular groove in the recipient cornea into which we sewed it. It seemed to have lots of advantages, it didn't require fresh donor material, it had no living cells and was therefore non-antigenic and free from the problem of rejection, and it caused flattening and regularisation of the corneal profile which is what we wanted. Furthermore it didn't prevent us from doing a future operation. But it was found to be only suitable for mild or moderate cases. Scarring of the recipient cornea was still there afterwards, there could be interface opacities and these caused low light contrast sensitivity (in everyday language, patients couldn't see very well in the dark and didn't tolerate glare).
Various other techniques have been used - it's a rapidly expanding area. At a cornea conference last weekend there was a very interesting talk from people working in a corneal unit in Holland using all sorts of exciting new techniques, including a combination of laser work and surgery, of which we shall no doubt hear more in the future.
Sometimes we do other operations in KC - some of you may have had this. If you get a little raised area on the cornea which we call a 'proud nebula' we slice it off in some cases, either using a tiny knife or using a laser and that may make the difference between being able to wear a lens or not, which in turn may make a difference between continuing with your own cornea or having someone else's put in.
So what can we say about corneal surgery and keratoconus? Well despite the fact that we do it and believe in it, we have to admit it is both imperfect and irreversible. However difficult contact lenses may be to fit, and however frustrating they may be to wear, they are worth tolerating if they continue to produce good vision and pose less risk to the final outcome.
Various lens options eg 'piggy back' system of a hard lens on top of a soft lens, or a hybrid lens (hard centre and soft periphery) are possible and work for a small number of patients. The scleral lens is another solution which saves the patient from the surgeon in many cases. We have developed the modern version of this lens at Moorfields.
So the message I have for my surgical colleagues is that they should keep their kc patients in contact lenses (of all types) for as long as is humanly possible.
At this point questions were invited from the floor
Q. I've had 2 corneal grafts - 1 in '72 and 1 in '76. What is the life of a graft - people give you different ideas?
A. It's believed that the normal cornea, the one we're born with, could last much longer than a life time. We take advantage of that every time we do a transplant. The process of doing the operation means limiting the life span of the cornea because of damage to the endelothelium - nevertheless we think in terms of a transplant lasting the life of the recipient. We don't plan to replace it after 20 years, we think of it as being once and for all and that's why we're rather thoughtful about donor age and recipient age. I personally like to match them fairly closely.
Q. I can't wear contact lenses any more, my eyes are so super sensitive, my consultant has now registered me as partially sighted. Can forceps delivery have an effect on kc - I ended up with a lovely black eye!
A. Forceps delivery can cause corneal damage, but obstetrics has improved a lot and this sort of damage is very rare these days. However it does not produce KC, I promise you. We think KC is genetically determined and a pair of forceps can't alter that.
Q. Is there a distinction between the outcome of a transplant for KC compared to transplant performed for other reasons?
A. Yes, the chances of success are better in KC. We call such a transplant simple because there are no other disease processes, the eye is otherwise healthy, it doesn't have glaucoma or other inflammation and the chances are that there are no significant have blood vessels in the recipient cornea so you get a better result. KC is the biggest single indication in this country for corneal transplantation, also has the best prospect in terms of avoiding rejection.
Q. Can you say more on the heredity of kc?
A. It can be inherited but not inevitably. We see cases arising where seem no-one in the family has it or anything resembling it and others where there is a long pedigree of kc. We recognise that kc is a sliding scale - what we recognise clinically is possibly the tip of an iceberg. There are patients with thin corneas, high astigmatism, astigmatism in unusual angles - and we hope that some of the research we are doing will tell us more about the inheritance of all these variants.
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Page last updated: 19 February, 2015