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International Newsletter and Forum on Corneal & Scleral Rigid Gas Permeable Contact Lenses, Corneal Shape, Health and Vision
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I-site newsletter is a global newsletter which is purely educational in nature and launched in 2009, that monthly provides independent updates from the international literature on specialty (R)GP lenses and related topics. To unsubscribe at any time, click the link 'SafeUnsubscribe' at the bottom of this newsletter.
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Optical intervention for myopia. A phrase that sounds like a dream because myopia is probably the most common anomaly in our practices, we are the masters of optics; optics are the roots of our profession, and we are in the front line of the eyecare field. In addition, contact lenses currently have the best track record in that category. Still, though, there are so many questions regarding this type of intervention. Work by
Cheng, Brennan, Toubouti and Bullimoreat ARVO looked at the cumulative treatment efficacy of myopia intervention. Datasets from 11 orthokeratology, 6 soft multifocal and 4 spectacle lens treatments were included in the model. The projected maximum treatment efficacy for cumulative absolute reduction in axial elongation was 0.48mm, which is equivalent to a little bit more than 1D (after 7 years of treatment). This shows that we have to very careful, and it can be misleading to use percent treatment effect (as in '50% reduction' and such). See also, with a clinical perspective on this, Steve Turpin's '
Practically Abstract'. Furthermore, we should perhaps also focus more on 'delaying myopia onset' rather than just trying to reduce progression. And while we may not be able to get the 'mileage' that we want/seek, it also is apparent that every diopter counts in myopia prevention. But maybe we should revisit our approach to myopia management. Hence: manage the myopia management.
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Orthokeratology versus Low Dose Atropine
Atropine was not included in the model used in the study described above. Atropine in higher concentrations has proven to be very effective but also has more side-effects. Lower concentrations of atropine treatment were for a long time the most promising kid-on-the-block. But lately, more and more reports show that low-dose atropine is not as effective in the long run as originally thought and advocated. A recent study by Lyu et al looked at 0.02% atropine versus orthokeratology in a large cohort of patients (247 children) followed for a relatively long period (2 years). The children were 7-14 years of age with a cycloplegic refraction of -0.75D to -6.00D and astigmatism <2D. They found orthokeratology to be the better method for controlling axial length elongation compared with 0.02% atropine: axial length elongations were 0.36±0.30mm and 0.58±0.35mm respectively after 2 years of treatment (p=0.007).
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Long-term Orthokeratology Effect Prediction
In light of the last item, a paper by Zao et al. states that it would be very helpful for clinicians to be able to predict the efficacy of orthokeratology on myopia early in the course of the treatment to provide other effective treatments such as adding low dose atropine if needed. Their study tries to do exactly that: to investigate whether short-term axial length changes in children undergoing orthokeratology can be predictive in the long term. The study concludes that indeed it is possible to use the half-year axial change data to predict long-term myopia development over a period of three years of wear. When looking at other variables, and in contrast maybe with previous results, no correlation between spherical equivalent refraction and short-term axial length was found nor between pupil diameter and short-term axial length. They did, however, find, in line with previous studies, that older age was correlated with a smaller increase in axial length.
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| Orthokeratology Lens Fitting |
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Orthokeratology in Astigmatic Myopic Children
In fitting orthokeratology lenses for myopic children and for patients with astigmatism in particular, patient selection is key. Improper fit may result in lens decentration or a poor lens fit, etc. It is key to recognize that fitting ortho-k lenses is not a 'one-size-fits-all' approach. When fit properly, toric ortho-k lenses can significantly help young patients who were previously thought to be poor candidates for ortho-k lens wear. A thorough understanding of corneal contour and characteristics is vital to ensure successful ortho-k fitting for myopia management, writes Kevin Chan in Orthokeratology in Practice. More importantly than lens fit maybe: a poor lens fit may compromise the myopia treatment effectiveness.
Image: Michael Baertschi/Michael Wyss
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| Orthokeratology Lens Fitting |
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Orthokeratology Fundamentals
Myopiaprofile.com provides a self-paced course in orthokeratology lens fitting. The course covers everything you need to know from understanding core concepts through to advanced material. It is designed to guide the participant through the theoretical and practical foundation needed to get started fitting the first few patients with the modality. Specifically designed for the new orthokeratology fitter, the module strives to help the fitter with key background concepts such as how to capture optimal topography images and select the right candidates and then steps through the lens fitting process, assessment of eye and lens fit after the first night follow up, the one week follow up etc. The module's instructor is Paul Gifford, and a free preview option to access the content from the introduction and the first module is free of charge.
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In the
last edition of I-site newsletter
the statement was made that we should not forget about corneal (R)GP lenses and that we should always keep looking for the best option for each particular patient, without making any prejudice to any lens type. Here is a case from Jeroen Duijkers from Maastricht in the Netherlands in reference to that statement and to illustrate it. It shows a beautiful fluorescein pattern of a nice stable corneal (R)GP lens fit with a visual acuity of 20/20- (1.0-) on an eye with a pretty challenging refractive error. The end result shows a corneal topography-designed toric multifocal (R)GP lens with base curves of 8.28/7.55mm in a
10.2 diameter
with a prescription of S+7.00 C-1.75 axis 166 degrees with a reading add of +2.50. The lens used is fitted based on the periphery of the cornea, bridging over the central cornea pretty much as the lens is lifting off of the central cornea (like a scleral lens actually) and where the height of the lens is not linked to the peripheral landing zone. Click on the image to see the fluorescein video to fully appreciate this work of art. And let's make sure to keep teaching the students in optometry schools around the world about the beauty of corneal (R)GPs.
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Risk Factors for Orthokeratology Case Contamination
Practically abstract by Steven Turpin looks at a study by Wang et al published in Contact Lens and Anterior Eye on risk factors for orthokeratology case contamination. Subjects were using cylindrical cases (25), flat cases with ridges (98), and flat cases without ridges (71). The biofilm on each lens case was stained, and the optical density of the biofilm was rated. The more biofilm present in the case, the more stain it retained and the higher the pigment density. Risk factors for higher degrees of contamination included using flat cases with ridges, replacing cases with a frequency of greater than three months, not rinsing the case with multipurpose solution (MPS), not drying the case with a tissue after applying lenses and storing cases in the bathroom. There was no significant difference between type of MPS solution used.
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I-site is an educational newsletter that is distributed on a monthly basis and provides an update on rigid gas permeable related topics (scientific research, case reports and other publications worldwide). I-site is objective and non-political. Its editor
Eef van der Worp, optometrist, PhD, FAAO, FBCLA, FIACLE, FSLS is a lecturer for a variety of industry partners, but is not related to any specific company. Please contact us at:
[email protected].
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