The British OrthoKeratology Society
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The British OrthoKeratology Society
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GOS 2004 Positively Orthok. The second Global Orthokeratology Symposium (GOS) was held in Toronto on July 22-25, 2004. With over 600 delegates from 34 countries this was the largest gathering of RGP enthusiasts ever held. I was looking forward to attending because with normal conferences there are usually some items on the agenda that one is not particularly interested in but, as this was exclusively dedicated to Orthokeratology, everything on the agenda looked inviting. As the only UK Speaker and, in fact, the only UK delegate I can honestly inform you that you all missed a terrific event. The only complaint I have about the organisation of the conference was that it started at seven o'clock in the morning with breakfast seminars and the main sessions continued from eight o'clock until 5 p.m. On registering we were given a ring binder with a printout of each Speaker's presentation with space to write notes. This proved extremely useful when I returned home as I could reconstruct each lecture. The BCLA would do well to emulate this. Thursday was an education day and an introduction to Orthokeratology fitting. This covered patient selection, pre-fitting evaluation, lens design, overnight orthok wear and problem-solving video case histories.
It is impractical to documented all the papers, so I will divided the conference content into three main groups, the Safety of Orthokeratology, the Corneal Response To Overnight Wear and New Lens Designs For Hyperopic Corrections And High Myopia.
The Safety Of Orthokeratology. In “The State Of Orthokeratology, A Worldwide Overview”, Jonathan Jacobson of Polymer Technology / B&L documented the experience in China. In 1998 there were 80,000 orthok wearers, this rose to 400,000 by 2000 but then dropped to 18,000 by 2002. The explosion in wearers was due to overselling to untrained contact lens fitters who had no topographers, no local labs, no direct relationship with laboratories, gave no follow-up visits to the patients and gave no clear instructions to the patient in case of emergencies. This resulted in many incidents of corneal ulcers and infections and the resultant adverse publicity reduced the wearing base. Nick Stoyan, one of the original orthok designers, said in March 2001 “The China experience is an accident waiting to happen.". This emphasises the importance of good practitioner training, equipment and patient education. Conversely only one case of serious infection has been documented in the Netherlands in spite of a large patient base. This was covered by Eef van de Worp who detailed the case of a 12-year-old orthok wearer who developed a Pseudomonas infection after orthok wear. Non-compliance to the care regime may have been a factor. Brien Holden covered infection and bacterial binding concerns and stated whilst this was an important consideration only three cases of microbial infection have been documented outside Asia. All the others have been in China and Hong Kong and were due to the above circumstances. Marjorie Rah detailed 5 case summaries of microbial keratitis and thought that compliance played a key role as the causative factor for the adverse reactions, with over wear being the most common type as some of the patients were wearing their lenses day and night.
The Corneal Response To Overnight Wear Helen Swarbrick then spoke on Recent Research in Orthok. There appears to be central epithelial thinning with mid-peripheral Stromal thickening whilst the posterior surface of the cornea does not appear to be affected. Interestingly the overnight stromal oedemal response with orthok is less than with no lens present. This may be due to “clamping” pressure at the centre of the Orthok lens.
One of the most important papers was presented by Jennifer Choo with” Morphologic Changes In Cat Epithelium Following Overnight Lens Wear With The CRT Lens”. The cat was chosen because the cornea contains a Bowman's membrane. She showed histological slides of four hour, eight hour and 14 day wear with both myopic and Hyperopic orthok lenses. The four and eight hour results are important for our understanding of orthok because these mimic the normal wearing profile of our patients. Whilst the 14 day continuous wear, under a closed eye condition, is interesting it is an unnatural situation and hopefully not achieved by any of our patients. With the myopia lenses, the epithelium showed central thinning with mid-peripheral thickening and no increase in the number of cells. The hyperopic lenses showed significant central thickening with a slight thickening in the mid-peripheral region again with no increase in the number of cells. The proposed mechanism was cell compression in the case of thinning and cell enlargement when the epithelial thickened.
There are also appeared to be some stromal thickening in the 14 day study and these changes corresponded to the different parts of the orthok lens. Corneal reshaping is obviously multifactorial with the possible mechanisms being:
Unfortunately I am not able to provide the histology slides until the paper has been published. I will be able to show them, together with an expanded report of the GOS at the next meeting of the British Orthokeratology Society (BOKS). This is on Tuesday 26th October from 6.00pm at the Richmond Gate Hotel, Richmond, Surrey. Pease contact me if you wish to attend. 020-8894-7149.
Maseo Matsubara detailed the morphological findings of rabbit cornea produced by an orthok lens and concluded that there was a topographical redistribution of epithelial thickness with no apparent histological changes in the corneal epithelium. This reinforced the previous paper and elegantly showed how the different curves of an orthok lens induce different changes in the cornea according to the forces induced in that area.
Jou-Chun Lin in his paper on the effect of Orthokeratology on the morphology of central and peripheral corneal endothelium concluded that there was no significant change in corneal endothelial density after six months and no significant change in the morphology of the endothelium. The research was done using specular microscopy.
New Lens Designs for Hyperopic Corrections and High Myopia.
This is where it gets interesting; although I am keen to understand the mechanisms behind orthok, as a practitioner my main concern is to extend the fitting range of these lenses safely. The original single reverse geometry lenses would correct up to -2.00D, the first double reverse geometry lenses to - 3.50 and the latest designs can comfortably cope with a -5.00D prescription. We now had a number of papers covering high myopia correction and the latest innovation, hyperopia and presbyopia corrections. Although there are few applicants who are a hyperopic I think there is a great opportunity to fit monovision with these lenses to presbyopic myopes. Joe Sicari of Paragon explained his vision of CRT; saying that we should be thinking of orthok as a new modality in vision care and not just another type of contact lens. He estimated that in the USA only, without today's market constraints, there are 55 million people who fit the profile for orthok.
Hsiao-Ching Tung detailed the effect of the XC lens from Vipoc. With 323 patients in three years, the lens was effective for a range between -4D and -12D with an average of -7D correction. It was routinely used up to -10D and topography maps were shown of incredible results.
The following are the results using Vipok lenses by Bruce Williams of Seattle. The first shows a change of -7.9D and the second -8.5D
SLIDE 1 SLIDE2
This was the first time I have seen this kind of evidence and the usual explanation of corneal epithelium changes cannot explain these large prescription changes. Munylins formula gives approximately 6 mu. change for each dioptre which would mean a 60 mu. change in corneal epithelium for a -10 correction. This is obviously not possible so other factors must be taken into account. There may be an alteration in anterior chamber depth as well as posterior corneal shape changes.
Hyperopia orthok lens designs are being developed by all the major manufacturers. They achieve the effect of steepening the central cornea by exerting force on the peripheral cornea by careful lens design. Interestingly, the CRT lens can be used for hyperopia correction without any change in the lens design.
Slide 3 There are three adjustable parameters to this lens; the BCOR which is the moulding curve, the lens Sag and the landing zone angle (LZA). One takes the flattest K. reading and steepens it by the amount of refractive change required. The LZA dictates the fit and is obtained by use of the appropriate lens from the fitting set. The lens sag will be lower than the range used for myopia control, usually 500 to 575, at 400 to 475u. Again this can only be established empirically. Clinical trials are being undertaken and hyperopic fitting sets will be available shortly. Jerry Legerton detailed these lenses and showed that approximately +3.00D changes can be achieved. The normal bulls-eye appearance of a myopia orthok lens is enhanced with the addition of a central fluorescein pool giving five distinct regions instead of four.
Slide 4 Slide 5
Presbyopia designs are also under development with the aim of inducing a centre near multifocal shape to the cornea. Changes of around 3.00D are possible with adequate distance vision and good near vision performance.
Slide 6
The days started with manufacturers breakfast seminars at
seven o'clock and, whilst these were somewhat taxing to get to, they were very
informative. We also had the opportunity to meet them in the exhibition hall
which was open until 7 p.m. each day.
Polymer technology hired the restaurant at the top of the CN Tower for the Saturday evening soiree. The food and drink were available in abundance and, as the restaurant revolved slowly, some delegates found that facing the wrong way was not advisable after sampling their host’s hospitality. I have to say that this was one of the best organised and most enjoyable conferences I have ever been to and Craig Norman, Patrick Caroline and all the organisers have to be congratulated. Toronto is a terrific city and, as we travelled around Ontario before the conference, I can recommend it as a holiday destination. I am also looking forward to the next GOS and I am working on my next presentation for it. Slides 7,8,9
Basil H Bloom BSc(Hons) FCOptom 121 Addington Road Selsdon CR2 8LH 020-8657-2000
Independent Practitioner Treasurer BOKS
The next meeting of BOKS will be on Tuesday October 26th 2004 from 6.00pm at The Richmond Gate Hotel, Richmond Hill, Richmond Upon Thames, Surrey TW10 6RP Tel:020 8940 0061 Fax:020 8332 0354. The provisional agenda is Report on GOS2 OrthoK Lens from No7 Hyperopic Orthok lens designs - Bruce Williams USA High Myopic OrthoK – Frank Spors Germany
All are welcome. Please inform Basil Bloom 020-8894-7149 Mail@boks.org.uk if you wish to attend. |
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The British Orthokeratology Society
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