what does this mean?Corneal Cross-Linking

[GeorgeThe2nd]

http://www.iovs.org/content/54/2/1181.full
The Efficacy of Corneal Cross-Linking Shows a Sudden Decrease with Very High Intensity UV Light and Short Treatment Time

Paolo Vinciguerra

+ Author Affiliations

Istituto Clinico Humanitas Via Manzoni, 56. Comune, Rozzano (MI) Italy; info@vincieye.it





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Several papers have been published in previous years regarding cross-linking and the effect of the procedure on corneal ectasia. Different protocols of cross-linking have been described with or without corneal epithelium removal, with different kinds of riboflavin solution (e.g., hypo-, iso—hyper-osmolar), different impregnation times, and different lengths of UV-A illumination and irradiation power. The huge amount of information could disorient the general ophthalmologist, who has to choose the proper procedure and, moreover, decide the best protocol to treat the patient.

The study by Wernli et al.1 shows in a large number of cases, the biomechanical strengthening effect of cross-linking with various irradiances ranging from 3 to 90 mw/cm2 with illumination times from 30 minutes to 1 minute, respectively. These results show that for irradiances larger than 45 mW/cm2, corresponding to an illumination time of about 2 minutes, there is no significant increase in corneal strengthening.

Considering the different tools commercially available and the various ranges of UV-A irradiances, the ophthalmologists, who are not accustomed with cross-linking procedure, could find the approach to cross-linking difficult and confusing; they could erroneously think that a faster procedure would be effective enough and without any side effect, like the original Seiler's protocol.

This paper is crucial because it gives precise information regarding the effective strengthening of the cornea at various irradiances.

As the authors suggested, other papers will be needed to validate these results in vivo, study the possible side effects of higher doses of UV light at lower exposure times and consider the flattening effect of the different protocols. The flattening effect of cross-linking over the corneal stroma tended to regularize the corneal shape and allow variation in refraction with increase in best spectacle-corrected visual acuity in several patients. It was not necessarily related to the increase of the biomechanical strengthening of the cornea.

[longhoc]

Hi George, this is really a very interesting find, thanks for posting it. It is interesting because it touches an important aspect of Crosslinking and how it is not a done-deal, there's is a commonly undertaken way of doing it but there is potential for the procedure to be enhanced.

Only a layperson's opinion, but the paper was apparently making the following points (in the somewhat laboured language of medical academia !):

1) There are various different methods to do Crosslinking
2) The different ways can give different outcomes in terms of strengthening the eye and flattening it (these two outcomes are what the procedure wants to achieve)
3) No-one is quite sure which of these methods produces what sorts of outcomes
4) More research is needed to get to the bottom of it all

By way of background, which isn't mentioned in the extract you provided, there is a "mainstream" established protocol for Crosslinking which defines that:

1) the epithelium should be removed
2) a specified quality of
3) a specified version of riboflavin
4) should be used for a specified time
5) with a specified wavelength of UV

With at least five variables in play there's plenty of scope for trying to get more targeted results. And I've simplified this list, for example even if it is "epi off" i.e. with the epithelium removed there's different methods for how this should be done.

It all reminds me of my mother-in-law putting flowers in a vase. I, if for some unfortunate circumstance I end up having to do this task which I regard as a chore, just plonk them in the vase straight out of the wrapper. The aforementioned mother-in-law goes to town, tweaking stem lengths, individual flower placement, water level, quantities of flowers (sometimes one vase is used, sometimes two for seemingly inexplicable reasons and apparently at random although I am resoundly assured there is logic at work).

But I digress. There's lots to tweak with Crosslinking too and the clinicians are going to continue tweaking the variables in order to find out what changes what, and why.

Best wishes

Chris

[GarethB]

This is exactly why NICE looked in to this and decided a few years abck that further work was needed before they would recomend if this shoud or should not be available on the NHS.