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Post Info TOPIC: UK experience of Corneal Collagen Cross Linking (C3R)


Ophthalmologist

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Posts: 8
Date: Mon Jun 4 12:11 AM, 2007
UK experience of Corneal Collagen Cross Linking (C3R)
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Just over 2 years ago I learned about and began treating keratoconus and post-LASIK ectasia with cross linking. The long term results have been very good. No one has become and the majority have improved both topographically (corneal mapping) and in their unaided vision. Often the vision improves more  than would be expected than a crude interpretation of the map would suggest. This is because the regularity of the cornea improves and this shows up in the detail of the objective maps.
In the first 3 months or so results do vary considerably. Some see better in the first few days. Others improve steadily over time and some initially worsen but then steadily improve. Corneal maps can be confusing early on because of the initial corneal swelling which disappears after a few weeks.
So far there have been no serious complications. The worst problems have been the discomfort of the first 24-48hrs (helped by a bandage contact lens, painkillers and a smaller amount of cell removal before treatment). I have also been looking for signs of damage to the retina (the back of the eye which is like film in a camera). There have been none. I put this down to strictly following the guidelines. The cornea must be thicker than 400 microns at its thinnest and riboflavin drops must be applied for a full 30 minutes before 30minutes of treatment. As a result the doctor and patient get to know each other pretty well! If it is thinner there is still the Intacs corneal implants option. These are clear perspex implants placed in the cornea which is the front window of the eye. These require a thickness of 400 microns also, but only where they are implanted and not at the thinnest point. They flatten the cone of keratoconus and reduce the short sight. They also reduce the progression of keratoconus, but only cross linking truly treats the underlying problem. The two procedures work well together.
The 400 micron cut off ensures that with riboflavin dye blocking the ultra-violet light 99.85% is blocked before it gets to the lens and almost none reaches the back of the eye. It must be remembered that the power of this light is much lower than the ultra-violet light from the excimer laser used for short and long sight. It only stiffens the cornea rather than vapourising it. Early studies showed that if the power was raised too high or the cornea was too thin then damage occurred to the inner lining cells of the cornea.
The important point with the stiffening is that it particularly works in the first one third of the cornea which is normally the srongest and most important part of the cornea. In keratoconus and post-LASIK ectasia this is weakened. One possibility for thinner corneas is being studied. This involves the use of distilled water to artificially thicken the cornea temporarily so that it is over 400 microns thick.
The surface cells must be at least partially removed to allow riboflavin absorption. It is more comfortable to leave them, but this results in less effect.
The person must not have a central scar. Changing the shape will not benefit them, although PTK (photo-therapeutic keratectomy) using an excimer laser may reduce the scar.
Generally they should be under 40 as keratoconus tends to stabilise beyond this. However, if a person's eye is changing then it can be treated at any age for example after laser eye surgery (LASIK).
There should be no history of herpes simplex keratitis as this can possibly lead to scarring.
They must not be pregnant as this makes the results unpredictable.
In my experience the people who do best are the ones with K readings (a corneal steepness measurement) in the 50's. Under 47 is normal but in keratoconus this can rise to over 80. Below 50 there is less room to improve as it is already pretty good. Beyond 70 the cornea is usually too thin for cross linking and other options such as corneal grafting need to be considered. Until recently I have held off treating eyes with normal vision, but if the posterior float of the Orbscan shows early changes then it is worth treating as a precaution as over 90% of keratoconus cases affect both eyes.
In the year before I started treatment I saw 2 patients who came for surgery for their short sight and astigmatism. I turned them down on the grounds of their keratoconus. When I began using the cross linking machine I called them back and they had both worsened. However, in the six month period since treatment both have improved.
I have also treated a lady from Seattle in the US who was recommended to come to the UK by her ophthalmologist because it is not yet available there. She had already had Intacs in one eye. After the C3R she said she couldn't remember a time when her vision had been so good and she was able to walk around without glasses or contact lenses. The trip required a one week stay in London for both eyes to be treated separately and then she was able to return to Seattle for local follow up. I find more and more American interest in this, especially as they can see a doctor whose first language is English and their companions like the idea of staying in London for a week.
It is possible that younger patients will need further treatment in 5 to 10 years, but the older a person is the less likely it is to be a problem as stiffening of the cornea increases naturally with age.
In summary: I have found that cross linking works well. It may need to be combined with other procedures such as Intacs or Ferrara rings.
The important points for deciding whether or not a person is suitable for treatment
are: 1) 400 micron corneal thickness
2) Changing eye measurements
3) No central scarring
4) Steepness (K readings) less than 70
5) Not pregnant
6) No history of herpes simplex keratitis
 I believe that the original CE approved IROC system is superior to any other. It has adequate and steady power and needs to be 5 cm from the eye. This makes focusing easier than if it has to be closer. Some eye departments (including reputable NHS centres) have made their own machines, but these are unapproved and less predictable.
Finally it is a real pleasure to be able to treat people and give them the opportunity to avoid a graft which is normally needed by 1 in 5. I well remember how keratoconus patients were greeted with a groan by the doctor who had little to offer except to refer them to the optometrist who would do their best to make a comfortable contact lens. Now medical interest is much greater and there is much more hope for people with keratoconus and post-LASIK ectasia.

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London Centre for Refractive Surgery, 15 Harley St
London W1G 9QQ www.LCRS.co.uk
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