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Orthokeratology Review and Update
iGO SYNOPSIS: This Hong Kong study assessed 41 short-sighted overnight ortho-k corrective lens wearers aged between 8 and 36 through regular eye checks over a period of eight weeks to see whether wearing this type of lens only while sleeping was susceptible to a greater risk of infection than conventional daytime contact lenses. The results showed that those wearers who observed a consistently high standard of hygiene in lens cleaning and storage revealed no evidence of infection. Those whose lens cleaning and storage regime was inconsistent or not of a sufficiently high quality did reveal evidence of bacterial infection but this was resolved by improved lens hygiene. In particular, effective daily disinfecting of lenses after overnight wear using an appropriate lens cleaning solution and regular replacement of lens storage cases minimised the risk of any bacterial infection arising.
ABSTRACT
Orthokeratology (OK) is a clinical technique that uses specially designed rigid contact lenses to reshape the cornea to temporarily reduce or eliminate refractive error. This article reviews the history of traditional daily-wear OK (1960s to 1980s) and discusses the reasons for the recent resurgence in interest in the new modality of overnight OK, using reverse-geometry lens designs (1990s to the present). The clinical efficacy of the current procedure is examined and outcomes from clinical studies in terms of refractive error change and unaided visual acuity are summarised.
Onset of the effects of overnight OK lens wear is rapid, with most change after the first night of lens wear and stability of refractive change after seven to 10 days. Mean reductions in myopic refractive error of between 1.75 and 3.33 D and individual reductions of up to 5.00 D have been reported. There appear to be slight reductions or minimal changes in astigmatism with the use of reverse-geometry lenses and most patients are reported to achieve 6/6 unaided vision or better. The induction of higher order aberrations, in particular, spherical aberration, has been reported and this may affect subjective vision under conditions of low contrast and pupil dilation. Patient satisfaction with overnight OK has been reported as similar to or better than with other popular modalities of contact lens wear.
Available evidence suggests that the corneal changes induced by overnight OK are fully reversible. The refractive effect in OK is achieved by central epithelial thinning and this has raised concerns about compromise of the epithelial barrier to microbial infection. Recent reports of microbial keratitis in the modality are reviewed and the overall safety of the procedure is examined critically. Recent research on stromal contributions to the OK effect, particularly relating to overnight oedema, is summarised. Emerging issues in OK, including myopic control, correction of other refractive errors and permanency of the OK effect, are discussed.
June 2005, Optometry and Vision Science BOOST, MAUREEN V. PhD, FIBMS; CHO, PAULINE PhD, FAAO
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