The British OrthoKeratology Society
|
The British OrthoKeratology Society
|
|
|
THE GLOBAL ORTHOKERATOLOGY SYMPOSIUM 2005 Basil Bloom B. Sc (Hons) FCOptom, The third GOS was held in Chicago July 29-31 2005, at the Palmer House Hilton, one of the oldest and probably the most impressive hotels in Chicago. I am pleased to report that the United Kingdom delegation increased by 300% from last year. Over 360 delegates attended which did not include approximately 80 industry members; this was slightly down on last years meeting but still meant that the lectures and exhibition hall were always full. As a single subject conference, all the delegates were enthusiastic in their attendance and concentration; if they weren't interested they wouldn't be there, and as previously a lot of information was gained in informal talks at the bar after the official lectures. This does not mean to say that this was an easy conference to attend, the day began at 7am with manufacturers’ workshops, attendance was encouraged by the fact that breakfast was served there, followed by lectures proper from 8am finishing at 5 p.m. The exhibition hall closed at 7 p.m. and I must say the catering at this conference was the best I've ever experienced. The lectures covered new research and insight into old problems, some of which have bemused me for years. Thursday was entirely given over to the fundamentals of Orthokeratology where neophytes could get a good basic understanding of the subject before listening to the more advanced work at the conference proper. The first and second sessions covered Myopia and Orthokeratology and was moderated by Brien Holden.
Jeff Walline finally presented the results of the CLAMP study, Contact Lens And Myopia Progression. This was a 3 year study in which 59 subjects wore RGP lenses and 57 wore soft contact lenses. The results were
Over three years, the change was RGP -1.50 +/-0.95 SCL -2.19 +/-0.89 The change in corneal curvature accounted for half the effect which was not likely to be permanent.
Pauline Cho presented the LORIC study that she gave at BCLA. This is the Long-term Orthok Research In Children, the aim was to determine if orthok is effective in myopic reduction and control through a two-year study. 35 subjects completed the study and the findings, when compared to the control group of spectacle wearers showed
I feel this is one of the most exciting research results that I've ever seen. If it can be verified, and a lot of people are trying to do so, it means that we have a treatment for myopia. If we can fit the slightly myopic child with Orthokeratology lenses and prevent their myopia progressing we will become a therapeutic profession instead of one dispensing appliances.
The question immediately arises -- How Does This Work? Well Earl Smith from the University of Houston explained it in his “Mechanisms of Myopia” paper. The mechanism that triggers eye growth is peripheral defocus; if the periphery is hyperopic then the eye will grow to try to correct this. He pointed out that the peripheral visual plane was still hyperopic even when myopia is corrected as this only corrects the Central area. This also explains the finding that under-correcting myopia is worse than correcting it fully. Fig 1 Fig 2
One of the faults in orthok lenses is the large amount of spherical aberration that it induces, however this spherical aberration reduces the peripheral defocus and therefore reduces the stimulus for eye growth.
I mentioned in the introduction that a number of problems that had bothered me for years were answered. One of them was the situation in that orthok patients appear to see extra-ordinarily well even with residual prescriptions of up to -1.5D. Antonio Carlossi in his paper on the Multifocal Effect Of Corneal Moulding, had a couple of slides which showed that with spherical aberration, vision is clearer with a defocus of approximately -1.50D. He did not linger over the slides as he had obviously not heard the relevant questions being asked in the bar. Thank you Antonio, I don't have to worry about that any more. FIG 3
Patrick Caroline summed up the two sessions superbly covering the various methods of myopia control including bifocal lenses; all previous studies were plagued with patient non-compliance and therefore not valid, RGP's covered by the clamp study, pharmacology intervention using Atropine which has a terrific effect in reducing myopia but unfortunately has a large number of side effects with long-term cycloplegia,photophobia, possible macular damage, follicular conjunctivitis and toxicity! Pirenzepine (Atropine Lite?) shows some reduction in axial length change but has systemic complications.
The safety of Orthokeratology was again covered in a full session and Helen Swarbrick did an analysis of the first 50 cases of microbial keratitis in overnight orthok wear worldwide. One of the summary points was that it is premature to ascribe increased risk to overnight orthok compared with other contact lens modalities. A worrying factor is the high incidence of Acanthamoeba infections; tap water must not be used in lens care regimes at any time. Pauline Cho emphasised that the bathroom should not be used for any lens activity; insertion removal or cleaning. This applies to all contact lenses and not just Orthokeratology lenses.
There were a few papers on extreme shapes; Michael Berstsch described a design to correct high astigmatism with a spherical optic, an oval return zone and a toric back surface. Other designers are also working on this; Don Noack says that the BE toric lens will have an oval optic, oval return zone and a toric back surface. This will need topography elevation data from all four quadrants so make sure your topographer can do this, mine cannot.
Paul Woo described the high myopia treatment for children using the Vipok lens. This has a theoretical treatment limit of -10 dioptres. It works by increasing the peripheral pressure to push up the epithelium to enhance the edge of the treatment zone. If we visualise the treatment zone as a flattened volcano cone, the Vipok lens makes the walls higher and thus increases the power change. I was so impressed I ordered a trial set. Paul treated 30 children with prescriptions from -5D to -9D. He found that they tolerated the lens very well and were more active and out going in both their school and social life. Fig 4 Fig 5
Patrick Caroline described the use of CRT lenses for Post Lasik correction, a technique first developed by Bruce Williams. The original, pre-surgical topography data is used to calculate the lens but the edge angle is increased by 2°. As most of the prescription has been corrected by Lasik, the orthok lens only has to change a small amount and by using the original topography centration is good. I intend to try this when the next failed refractive surgery patient consults me. Fig 6
I have been asked a number of times if IOP in increases with Orthokeratology. I have to admit that I did not know the answer to this although my patients have not shown any increase. Maseo Mitsubara did clinical trials in Japan of an Orthokeratology lens and one of the findings was there was no significant increase in IOP.
Kevin Reader described his experiences fitting CRT lenses for Hyperopia. The maximum effect is +3.00 and is probably most useful for monovision. The usual CRT slide rule is used to calculate the LZA and RZD is reduced by 0.50. The base curve is calculated by taking the flatK + Change needed +0.50. (I have developed a spreadsheet to calculate this and hope to put it on the web site soon). Fig7 Fig8
Jenny Choo’s paper “The Use Of Soft Contact Lenses For Orthokeratology” has important implications for the future of orthok. The background to this is illuminating; this was discovered by accident at a University clinic, one of the patients attending had worn silicone hydrogel lenses inside out and presented with reduced VA. Topography showed a similar map to an orthok wearer. This was investigated and a number of high power minus silicone hydrogel lenses were made up for the study. They found that they obtained greater topographical changes from high powered minus lenses worn inverted, on a daily wear basis. They then examined the mechanisms using finite element analysis to simulate eversion of various soft lenses. They found that there was a low pressure area near the optic zone margin, high pressures in the mid-periphery and that pre stressing plays a key role in the performance of everted lenses. This research is ongoing to understand the optical and physiological principles behind Orthokeratology and to develop a soft lens for Orthokeratology.
Helen Swarbrick presented another paper on DK/T. this is not a subject that I usually find a fascinating but she managed to bring in a practical used for this. Two sets of orthok lenses were made, one in a low D. K. material (Boston ES) and the other in a high D. K. material (BostonXO). 12 subjects wore both types of Orthokeratology lens overnight and the results showed that that; 1. There was the same epithelial thinning with both materials. 2. BostonES showed overnight oedema. BostonXO showed no overnight Oedema. 3. BostonES had no significant clinical changes (no orthok effect) 4. BostonXO had significant clinical changes, flatter apical radius, improved VA and reduced Q. The conclusion was that high-level, overnight, stromal oedema overwhelmed the orthok effects with low D. K. materials. You should use high D. K. materials with Orthokeratology lenses to achieve the best effects. It also implies that the corneal effects are both epithelial and stromal.
Michael Lipson, in his paper, Overnight Corneal Reshaping Vs Disposable Soft Contact Lenses: Vision Related Quality Of Life Differences described a study of 65 subjects who wore both CRT lenses and daily disposable soft contact lenses. The results were slightly confusing to me. Of those subjects with prescriptions of under -2.50, 85% preferred the Orthokeratology lens, however only 40% with higher prescriptions preferred Orthokeratology. But when the quality of life differences were analysed both groups gave the same results.
A full session was dedicated to the subject of children and Orthokeratology which ranged from patient selection, reviews of clinical studies and practical examples. A useful tip I picked up was to feed the children immediately after lens insertion to take their mind off the procedure. Other practitioners emphasised the fact that you need to allow much more time for instruction with these children; one child needed six hours to become comfortable with removal and insertion but is now a successful orthok wearer.
John Mountford, who moderated the session on Topography gave a useful talk on “Expensive Corneas-when to say NO” and he was also in this years winner of the Roger Kame award which is given to the person judged to have made the most contribution to Orthokeratology.
Sunday morning was taken up with two sessions on marketing covering everything from patient information and education through public relations and informed consent and risk management.
There were 30 posters, including mine, and one of the most intriguing was entitled “Preliminary Studies Of The Stableyes Solution For Prolonging The Shaping Effect With Emerald Lenses”. This described the use of a solution called StablEyes to enhance the orthok effect. StablEyes is composed of Decorin, a naturally occurring proteoglycan which is present in most connective tissue. Results of previous testing in animal eyes have found that, when instilled into the eye, Decorin cross-links with fibrils in the corneal stroma. This has the effect of stabilising the shape of the cornea. StablEyes was administered as a single dose into the eyes of existing orthok wearers. The findings were that after three days the eyes with the solution were two thirds of the baseline prescription whereas the untreated eyes had returned to baseline. The delivery system was the most difficult to manage and more study is needed on the method used. If this can be perfected it may well be that we will be in a situation where orthok lenses will only be needed to be worn once a week. I look forward to further information from this source.
And innovation of this year’s conference was Bausch and Lomb’s Vision Shaping Treatment (VST) certification seminars. All the lenses which have FDA approval in the USA can only be fitted by practitioners who have been certified that they are competent to fit the lenses. An incentive was a U. S. B. flash memory dongle given to each participant who passed certification; and some dongles were programmed with a winning code for an Ipod. I chose to undertake certification on a lens I was unfamiliar with and I am pleased to reveal that I passed but unfortunately I did not win the Ipod.
With 45 papers and 30 posters this was a very intensive conference but please don’t think we had no time to relax. Polymer technology (B&L) hosted two superb events. A select group was invited for a Friday night cruise of the Chicago shoreline and they also hosted the main conference dinner at a conservatory in the naval pier on the shore of Lake Michigan. All the delegates were invited to this and it was a great opportunity to socialise in one group. After this party a number of us visited a blues club and then retired back to the hotel.
I have only been able to cover a small amount of the conference but I am sure you have gathered that I enjoyed myself enormously. The proposal is that next year's conference will be outside of North America and Amsterdam or Indonesia have been suggested as venues. I will try to attend wherever it is held.
I wish to thank B&L for their sponsorship of this event. Basil Bloom 2005.
Basil Bloom is an independent practitioner practicing in Surrey. He is a founder member and present treasurer of the British Orthokeratology Society. BOKS (www.boks.org.uk)
|
Copyright © 2005
The British Orthokeratology Society
|
