1

History

The wearing of rigid gas permeable contact lenses can produce changes in corneal curvature. [ ]. Orthokeratology (Ortho-K) may be defined as the planned, temporary reduction in myopia by the wearing of flat-fitting rigid contact lenses [ ]. The first deliberate application of this approach was reported in the early 1960’s when the “orthofocus” technique was described [ ]. Orthokeratology is referred to as Vision Shaping Treatment (VST) by Bausch + Lomb and Corneal Refractive Therapy (CRT) by Paragon Vision Sciences.

The first evaluation of orthokeratology was conducted in the 1970s by Kerns, who compared a group wearing flat-fitting rigid contact lenses during the day to both spectacle wearers and conventional rigid lens wearers [ , ]. Orthokeratology contact lenses were fit 0.25 to 0.50 D flatter than the flattest corneal meridian. Although a reduction in myopia (mean change = +0.77 ± 0.91 D) was observed after 300 days of orthokeratology lens wear [ ], Kerns still concluded that the procedure was unpredictable and uncontrollable as changes in refractive error ranged from a 2.62 D decrease to a 1.00 D increase in myopia along with induced astigmatism from lens decentration [ ]. Binder et al. compared subjects wearing flat-fitting PMMA contact lenses on a daily basis to conventional fitting PMMA lens wearing patients [ ]. Their orthokeratology lenses were fit between 0.50 D and 2.75 D flatter than the flattest corneal meridian. Like Kerns, Binder et al. felt that the procedure resulted in inconsistent and unpredictable reductions in myopia. In the early 1980s, Polse et al. conducted The Berkeley Orthokeratology Study [ ], a randomized clinical trial comparing a group wearing flat-fitting contact lenses daily to a control group wearing conventionally fit lenses [ ]. The mean reduction of myopia in the orthokeratology group was +1.01 ± 0.87 D as compared to +0.54 ± 0.58 D in the control group [ ]. Polse et al. again regarded these reductions to be variable and unpredictable as indicated by the relatively large standard deviations.

There then followed a decade of no peer-reviewed research on orthokeratology ( Fig. 1 ). This changed in the 1990s due to a convergence of three technologies: reverse geometry contact lenses, higher oxygen transmissibility and corneal topography instruments.

Peer-reviewed publications on orthokeratology over the past 55 years (source: Web of Science, 2020 Clarivate Analytics).

The original flat-fitting approach using conventional rigid contact lenses led to problems with centration of the lens on the cornea and accompanying poor and variable outcomes. Rigid gas permeable contact lenses for orthokeratology evolved into a new generation of designs, termed reverse geometry contact lenses [ ]. Wlodyga and Stoyan collaborated to develop a series of lenses wherein the base curve radius was designed to be flatter than the central corneal curvature, and the secondary curve steeper than the base curve radius. This created a reverse geometry lens. At the secondary curve junction, the lens and cornea formed a tear reservoir exhibiting a band of mid-peripheral fluorescein pooling. This design improves the centration and stability of the lens and led to more predictable and consistent reductions in myopia [ ].

Advances in oxygen transmissibility of rigid gas permeable materials further changed the practice of orthokeratology. The previously-described research used PMMA lenses. Materials have been developed that, in theory, should limit corneal oedema to levels normally occurring during sleep (i.e. 3–4% swelling) along with minimizing other ocular changes [ , ]. It should be noted, however, that these data are based largely on soft contact lens wear, whereas rigid lenses, including orthokeratology lenses, are smaller in diameter, but are also thicker. New materials provided oxygen transmissibility values that minimize, and perhaps eliminate, hypoxic stress and corneal oedema when worn on an overnight basis. Thus, overnight orthokeratology, also referred to as overnight corneal reshaping, became feasible, although overnight corneal swelling greater than lens-free values still occurs, particularly in the peripheral cornea, but may diminish in magnitude during weeks of overnight wear [ , ]. The potential advantage of this approach is that lenses are worn, the cornea is reshaped, and the level of myopia is reduced as the patient sleeps. Lenses are removed upon waking and good vision is obtained without correction through the day—an attractive feature for those with an active lifestyle. However, this myopia reduction is temporary, meaning contact lenses must be worn on a nightly basis to continue the effect.

Finally, corneal topographers had been developed, largely in response to the boom in refractive surgery. This allowed the orthokeratology practitioner to monitor the change in corneal curvature induced by the lens, the zone of the cornea flattened and its centration—reflecting the centration of the lens. Prior to this technology, the clinician had to rely on the less quantitative interpretation of fluorescein patterns and keratometry. Some contact lens manufacturers/laboratories will design an orthokeratology lens based on the topography and a few other parameters.

In 1997 Mountford published the first report of orthokeratology of patients wearing reverse geometry contact lenses on an overnight basis [ ]. Unlike the earlier evaluations of orthokeratology, Mountford reported more predictable and sustained reductions in myopia (pre-treatment mean = –2.19 ± 0.79 D; post-treatment mean = 0.00 ± 0.68 D; mean change = +2.19 ± 0.57 D). In a follow-up study, Mountford evaluated the retention and regression of the orthokeratology effect over a period of 8–9 h after contact lens removal [ ]. Most of the refractive changes occured within the first month of lens wear. Furthermore, Mountford found the amount of regression of the orthokeratology effect to be between 0.50 and 0.75 D during the day. While not explicit, greater regression would be expected in higher corrections. Modern designs incorporate a compression factor—an additional flattening of the base curve—to account for this regression.

Nichols et al. extended these findings, further quantifying the course of visual and refractive changes, the changes in corneal topography and thickness, and the extent to which these refractive and topographical changes are sustained throughout the course of the day [ ]. Ten myopic adults were fit with reverse geometry rigid contact lenses and examined at several times throughout the 60 days after commencing wear. Eight subjects completed the study and all visual, refractive, and topographic outcomes were sustained over the course of an 8 -h day. Mean uncorrected visual acuity improved from +0.52 ± 0.23 logMAR (6/20) to –0.04 ± 0.12 logMAR (6/5.5) by day 14. Mean manifest refraction was significantly reduced from baseline at day 60 (mean change = +1.83 ± 1.23 D) and was accompanied by significant central corneal flattening (mean change in apical radius = +0.20 ± 0.09 mm) and thinning (mean change = –12 ± 11 μm). Beyond 7 nights of wear, visual acuity was constant for 8 h following lens removal.

These and other studies established that overnight orthokeratology using rigid gas permeable contact lenses is effective in temporarily reducing myopia, providing good vision over the course of the day in myopes up to –4 D [ , ]. Subsequent studies have demonstrated the partial or complete efficacy of orthokeratology in patients with myopia up to –10 D [ , ]. The corneal changes that accompany orthokeratology occur much more rapidly than those noted in earlier studies, a finding likely due to reverse geometry orthokeratology lens designs and, possibly, overnight wear of the lenses. Most of the change in visual and refractive outcome variables occurred in the first seven nights of contact lens wear and asymptote around day 30. The visual and refractive changes that occur during overnight orthokeratology are well sustained through the course of an eight-hour day, but if lens wear is discontinued, refractive error will regress towards baseline. Around half of the myopia reduction will be lost after 24 h and 90 % within 72 h [ , ].

2

Regulatory history

In 1994, the United States Food and Drug Administration (FDA) granted the first daily wear approval for a lens indicated for orthokeratology for the Contex OK-Lens. In 2002, Paragon Corneal Refractive Therapy (CRT) lenses, manufactured by Paragon Vision Sciences, were granted FDA approval for overnight wear, with other lens designs and materials covered by the original approval. In 2003, Paragon received CE marking for their family of CRT lenses in the European Union. In 2004, Bausch + Lomb received approval for overnight wear of the Boston Vision Shaping Treatment (VST) lens. These contact lenses are marketed as a range of branded designs falling under the VST approval such as Contex OK E-system, Euclid Emerald, DreamLens and BE Retainer lens. In January 2017, the China Food and Drug Administration granted approval and commercial availability for Paragon CRT Contact Lenses in China. Like the US, Paragon’s China approval does not include any indication for myopia control, just temporary myopia reduction. In May 2019, Menicon received the first and only CE-mark approved orthokeratology lens for myopia control: Menicon Bloom.

3

Contact lens market penetration by orthokeratology

Cope et al. conducted a population-based survey to estimate the number of contact lens wearers aged 18 years or older in the United States [ ]. The authors estimate that that there are 40.9 million contact lens wearers aged 18 years or older of whom approximately 6.5 % are RGP lens wearers (2.7 million). The authors did not survey children nor did they ask specifically about orthokeratology.

For five years, Efron et al. asked practitioners in 38 countries to document their first 10 contact lens fits (new or refits) after receiving the questionnaire [ ]. Patients under 18 years old accounted for 13.2 %, but the proportion varied among countries, ranging between 25 % in Iceland to 1% in China. Orthokeratology fits represented 28 % of all rigid contact lenses prescribed to minors, including 47 % among 6–12 year-olds. The authors reasoned this proportion was due to the popularity of myopia control. These data represent the proportions of contact lens fits rather the wearers and may thus overestimate the proportion of children in the total population of wearers, although the mean age for new fits did increase from 28 years in 2002 to 32 years in 2014. Also, the response rate was 13 % and leaving the potential for respondent bias.

Morgan et al. recently reported 14 years of data from contact lens fitters, each reporting on at least 500 contact lens fits in 45 countries creating a database of 295,044 contact lens fits [ ]. Overall, orthokeratology lens fits represented 1.2 % of all contact lens fittings with a range of 0% in some countries to 6% in the Netherlands. The overall extent of orthokeratology contact lens fitting has risen slowly each year through the 14 year survey period, increasing from 0.5 % in 2004 to 1.3 % in 2017. Compared to non-orthokeratology lenses, orthokeratology lenses were also fit to a younger population (25 ± 13 years vs. 40 ± 15 years). The overall increase in prescribing orthokeratology and the younger age population likely reflects its increased use for myopia control.

Wolffsohn et al. reported on 971 respondents for a self-administrated, internet-based questionnaire distributed globally [ ]. Orthokeratology was perceived to be the most effective method of myopia control, followed by increased time outdoors and pharmaceutical approaches. Among effective myopia therapies, orthokeratology was the most frequently prescribed myopia correction option for progressing, young myopes in all regions with frequencies around 20 % in Australasia and Europe but only 10 % in Asia and the Americas. While the authors assert that the survey was “completed both by people cynical and enthusiastic to the issue,” the extent to which the findings can be generalized is uncertain. The survey results have recently been updated [ ].

4

Mechanisms underlying refractive changes

The prevailing wisdom was that orthokeratology flattened the cornea by bowing of the cornea, but limitations in instrumentation prevented testing this or alternative hypotheses. Swarbrick et al. provided the first insight into the anatomical changes due to orthokeratology [ ]. They found significant central corneal epithelial thinning, accompanied by thickening of the total mid-peripheral corneal thickness. Nichols et al. confirmed the central thinning of the cornea but were unable to show significant changes in the mid-peripheral thickness of the cornea [ ].

Overnight in the absence of contact lens wear, the corneal swells by 3–4%, and this oedema is increased by overnight wear of most lenses. Haque et al. evaluated both corneal and epithelial thickness changes after 4 weeks of overnight CRT in 23 subjects using optical coherence tomography [ ]. After the first night of wear, the central and paracentral cornea swelled significantly by 4.9 % and 6.2 %, respectively. The central epithelium thinned by 7.3 %, and the mid-peripheral epithelium thickened by 13 %. Corneal swelling recovered within the first 3 h after lens removal. Maximal overnight central epithelial thinning was 13.5 % and attained after four nights of wear. Three days after lens wear was discontinued, both corneal and epithelial thickness returned to baseline values.

Reinstein et al. reported a single case measuring a patient’s epithelial, stromal, and corneal thickness using high-frequency digital ultrasound, before and during orthokeratology treatment [ ]. The central epithelium thinned by 18 μm and the mid-peripheral epithelium thickened by up to 16 μm. They concluded that refractive changes were mainly induced by alterations in epithelial thickness and, while stromal changes may occur, their contribution is limited.

Qian et al. evaluated topographical changes in epithelial thickness using Fourier-domain optical coherence tomography (OCT) in 60 children fitted with myopic orthokeratology lenses and 44 control children [ ]. Epithelial thickness of the central 2 mm was significantly thinner in the orthokeratology group. Superior and inferior midperipheral corneal epithelium were thickest in patients with more than 14 days of orthokeratology wear.

Recently, Lau et al. fit orthokeratology lenses of different compression factors (0.75 vs 1.75 D) in 28 children (aged 7–11 years) and measured ocular components weekly for one month of lens wear and for three weeks after discontinuing wear [ ]. Again, central corneal thickness decreased by 9 μm at week 1 and stabilized for the remaining period of lens wear. Interestingly, anterior chamber depth decreased by 41 μm after one week of wear and was stable thereafter. Anterior chamber depth rebounded in the first week after cessation of wear. Corneal bowing or other posterior surface changes could contribute to these anterior chamber depth changes, although the authors believe them to be associated with accommodative changes.

There is some additional evidence, albeit equivocal, that the posterior cornea undergoes some changes as a result of overnight orthokeratology. Owens et al. fitted 19 young myopes with orthokeratology lenses that were worn nightly for a month [ ]. Central and midperipheral corneal thickness, topography and posterior corneal radii were evaluated within two hours of waking on four occasions. Significant anterior corneal flattening was observed after one night and beyond, along with significant posterior corneal flattening after one week. In contrast, Yoon and Swarbrick found no change in posterior corneal radius, although they did observe a more oblate shape, while acknowledging that their posterior geometry was calculated rather than measured [ ].

Chen et al. reported changes in, and recovery of, posterior corneal curvature after 6 months of overnight orthokeratology in 28 young adults [ ]. Posterior corneal curvature was evaluated using rotating Scheimpflug imaging. The posterior cornea significantly steepened after the first overnight lens wear, but these changes were not observed at subsequent visits. The posterior cornea was steepest immediately following lens removal and significantly flattened two hours later.

Finally, Gonzalez-Mesa et al. evaluated the effect of overnight orthokeratology on anterior chamber depth and posterior corneal curvature over one year [ ]. A significant reduction in anterior chamber depth and a flattening posterior corneal curvature was observed over the year.

In summary, the refractive changes that accompany orthokeratology are due to local changes in corneal epithelial thickness—central thinning and mid-peripheral thickening—thereby flattening the central cornea.

5

Efficacy of overnight orthokeratology for myopia control

Practitioners began discussing the viability of orthokeratology for myopia control around the beginning of the millennium [ , ]. The first peer-reviewed report of its efficacy was published in 2005 [ ]. Cho et al. enrolled 43 children fitted by eight private practitioners, of whom 35 completed two years of follow up. A historical control group of 35 children wearing single-vision spectacles from an earlier study was used as a comparison. The increase in axial length was 0.29 ± 0.27 mm and 0.54 ± 0.27 mm in the orthokeratology and control groups, respectively. Note that because of the change in transient corneal curvature and refractive error induced by orthokeratology, nearly all studies present effectiveness in terms of axial elongation. Axial elongation is the underlying cause of myopia progression and the two are highly correlated. For reference, a 0.1 mm difference is equivalent to around 0.25 D [ , ].

The results were confirmed by Walline et al. who used a historical comparison group of 28 soft lens wearing children [ ]. Forty subjects, 8–11 years old, were fitted with overnight orthokeratology contact lenses and followed for two years, with 28 completing the study. In spite of being conducted on an ethnically different population, the study showed results remarkably consistent with those of Cho et al. [ ]. The increase in axial length was 0.25 ± 0.22 mm and 0.57 ± 0.51 mm in the orthokeratology and control groups, respectively.

A number of subsequent studies were published, generally showing similar results. These are summarized in the comprehensive tables below ( Table 1 and 2 ) [ , , , ]. Only studies with a control group and axial length data are listed. The first randomized clinical trial randomized 102 children, 6–10 years old, to either orthokeratology or spectacles [ ]. For the 78 patients completing the two-year study, the mean axial elongation was 0.36 ± 0.24 and 0.63 ± 0.26 mm in the orthokeratology and control groups, respectively.

Table 2

Results of 11 peer-reviewed studies of the efficacy of orthokeratology for myopia control.

Study (year)	Drop Out (%)		Axial Increase (mm)		Treatment Effect (mm)	Included in Meta-Analysis?
	Ortho-K	Control	Ortho-K	Control		Si (2015)	Sun (2015)	Wen (2015)	Li (2016)
Cho (2005)	17	NA	0.29 ± 0.27	0.54 ± 0.27	0.25	*	*	*	*
Walline (2009)	30	NA	0.25 ± 0.22	0.57 ± 0.51	0.32	*	*	*
Kakita (2011)	7	17	0.39 ± 0.27	0.61 ± 0.24	0.22	*	*	*	*
Hiraoka (2012)	24	30	0.45 ± 0.29	0.71 ± 0.35	0.36			*	*
Santodomingo (2012)	6	20	0.47 ± 0.18	0.69 ± 0.33	0.22	*	*	*	*
Cho (2012)	27	20	0.36 ± 0.24	0.63 ± 0.26	0.27	*	*	*	*
Charm (2013)	54	38	0.19 ± 0.21	0.51 ± 0.32	0.32	*	*	*	*
Chen (2013)	19	38	0.31 ± 0.27	0.64 ± 0.31	0.33	*	*	*	*
Chan (2014)	—	—	0.61	0.80	0.19				*
Zhu (2014)	NA	NA	0.34 ± 0.29	0.70 ± 0.35	0.36				*
Pauné (2015)	38	49	0.32 ± 0.20	0.52 ± 0.22	0.20

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related

Related posts:

1. On the in vivoassessment of goblet cells of the human bulbar conjunctiva by confocal microscopy – A review
2. Assessment of compliance with contact lens wear and care among university-based population in Jordan
3. The effect of sodium fluorescein on anterior eye surface measurements
4. Bacterial biofilm in silver-impregnated contact lens cases

Stay updated, free articles. Join our Telegram channel

Join