International survey of orthokeratology contact lens fitting
Introduction
Orthokeratology (OK) has been discussed in the refereed literature for over half a century, with a PubMed search for the term ‘orthokeratology’ revealing the first paper on the subject to have been published by Ziff in 1968 [1]. In its original form, OK involved wearing flat-fitting hard lenses made from polymethyl methacrylate (PMMA) during the waking hours, with the intention of progressively flattening the cornea to reduce the degree of myopia, so as to afford reasonable vision following lens removal [2].
The introduction of highly gas-permeable rigid materials, reverse geometry designs and instrumentation to monitor changes in corneal topography has allowed the correction of low to moderate levels of myopia and astigmatism with OK lenses, shifting the approach from daytime wear of lenses to overnight wear (so-called ‘overnight orthokeratology’ [3]). Contemporary OK lenses are worn overnight to induce a flattening of central corneal curvature to temporarily correct myopia, and are removed upon waking to provide reasonable vision throughout most of the waking hours [3]. Practitioners fitting such lenses are obliged to weigh up the benefits of this approach (minimizing lens discomfort due to closed-eye lens wear during sleep) versus the disbenefits (increased risk of microbial keratitis during overnight lens wear [4]).
More recently, it has been proposed that OK has an additional benefit of arresting the progression of myopia (so-called ‘myopia control’) [[5], [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17], [18], [19]]. This is thought to occur as a result of the optical configuration of reverse geometry lenses and its impact on peripheral corneal molding, whereby positive spherical aberration in the molded corneal periphery creates an apparent reduction in the optical stimulus for eye growth [20].
Although there has been much discussion about OK in the referred literature, clinical magazines, internet forums, conferences and the like, little is known of the true extent to which these lenses are fitted around the world. This paper examines trends in, and factors associated with, OK contact lens fitting in 45 countries over a 14 year period (2004-2017, inclusive). Such information can provide (a) a valuable yardstick for contact lens clinicians, against which they can assess their own prescribing approaches to OK, and (b) useful guidance to the contact lens industry on the clinical utilization of this specialist lens category.
Section snippets
Conduct of the annual survey
Between January and March each year from 2004 to 2017, a contact lens fitting survey was distributed in 45 countries. This was achieved through the offices of members of the International Contact Lens Prescribing Survey Consortium (see Acknowledgements), which is a network of academics, industry representatives, and clinical colleagues who have agreed to manage the survey in their country or geographic region, as outlined below.
Each Consortium member was requested to send a paper or electronic
Demographics
Data were accessed from 45 countries, each reporting information about at least 500 contact lens fits, during the 14 year survey period (2004-2017). This generated a database of 295,044 contact lens fits, of which 2,702 were with OK lenses and 292,342 were with other lens types (non-OK). The median country response rate was 3,197 fits over this period, ranging from 508 fits in Egypt to 61,731 fits in Japan.
OK lenses represented 1.2% of all weighted contact lens fits; however, there was
Discussion
Differences in the extent of OK lens prescribing between nations may be attributed to international differences in the training, attitudes and collective confidence of the predominant practitioner groups – opticians, optometrists and ophthalmologists. For example, ophthalmologists, who largely or exclusively manage serious contact lens-related eye infections in many regions of the world, may harbour more conservative attitudes and concerns relating to the ocular health risks of overnight OK
Conclusion
OK is a niche contact lens fitting modality, which is employed to a greater extent by eye care practitioners in some European countries where there is a culture of rigid lens fitting supported by local laboratories capable of fabricating these lenses. Typically, OK lenses are fitted in high Dk materials on a planned replacement basis to younger patients, presumably for the primary purpose of arresting the progression of myopia.
Declaration of interests
None.
Acknowledgments
The International Contact Lens Prescribing Survey Consortium: Philip B Morgan, United Kingdom; Nathan Efron, Australia; Craig A Woods, Australia; Jacinto Santodomingo-Rubido, Spain; Carmen Abesamis-Dichoso, The Philippines; Suresh Awasthi, Nepal; Joseph Barr, United States of America; Marion Beeler-Kaupke, Switzerland; Jitka Belikova, The Czech Republic; Vadim Belousov, Russia; Jolanta Bendoriene, Lithuania; Janet Casablanca, Puerto Rico; Aris Chandrinos, Greece; Prema Chane, India; Patrick
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