Report

Myopia control an undercurrent at orthokeratology congress

The Orthokeratology Society of Oceania (OSO) and the International Acady of Orthokeratology (IAO) held a joint congress (OSO’s 12th and IAO’s 5th) in Surfers Paradise, Queensland from 23–25 Septber.More than 270 delegates and a large number of exhibitors covering most aspects of the specialised contact lens industry attended. The opportunity was taken to confer IAO fellowships on seven OSO mbers including four from Australia and three from New Zealand.As orthokeratology (ortho-k) is a bastion of highly specialised rigid contact lens (CL) fitting, the discipline now finds itself enmeshed in the related fields of myopia control and the rise of scleral and miniscleral CLs as an answer to sometimes perplexing fitting issues, often involving pathological conditions of the anterior eye. The two and a half day program had myopia control as an ever-present overtone.During the event’s opening, the creation of a new organisational entity, the International Acady of Myopia Control, was announced – a timely development in light of the meeting’s dominant the and the world’s myopia ‘probl’.Despite the new and the established information presented at the meeting by well-known presenters – a selection of which have been summarised below – perhaps the most noteworthy feature of the event was the surprise ‘retirent’ announcent by Dr John Mountford.ORTHO-K GURU ANNOUNCES RETIRENTBrisbane-based Dr Mountford was one of the main shakers and movers behind ortho-k in Australia – and eventually the world – as well as being behind the foundation of OSO. He is perhaps best known as the ‘father’ of the BE ortho-k lens series developed in collaboration with the late Mr Don Noack of Capricornia Contact Lenses in Brisbane.{{image2-a:r-w:400}}In announcing his retirent, Dr Mountford allayed fears that he was abandoning the field by stating that he would rain involved but as a conference delegate, mentor, and consultant. Speaking with Insight on the decision, Dr Mountford explained that he wished to enjoy his involvent in ortho-k rather than be a constant contributor to its conference programs.The unexpected news followed Dr Mountford’s presentation, which provided a brief overview of current ortho-K thinking. He stated that greater mid-peripheral steepening resulted in increased myopia control but that the relationship between initial myopia and final myopia was less clear. He also noted that with respect to the treatment zone, while there was no difference between axial or refractive topographical plots, a tangential plot would display a difference.In passing, he mentioned that treatment zones larger than the entrance pupil of the eye were pointless. Therefore, the pupil size must be accounted for when deciding on the size of the treatment zone to be used. To monitor mid-peripheral steepening however, an axial power map is needed.A factor not spoken about much is the modulus of elasticity (Young’s modulus) of Bowman’s layer. It is about 10X that of the epithelium, which means it is probably a limiting factor on the magnitude of changes that can be made simply by flattening the epithelium alone. How thin the epithelium can be made and survive largely unaltered is probably the other limiting factor.AXIAL LENGTH MEASURENT IN ORTHO-KDr Zhi (Peter) Chen is a full-time physician at the Fudan University Eye and ENT Hospital in Shanghai, China, and a senior fellow of the International Association of Orthokeratology Asia. He started his presentation by stating that axial length (AL) shortening was, in fact, a shortening of the vitreous chamber. Such AL shortening in ortho-k was first noted by Prof Helen Swarbrick of the Research in Orthokeratology (ROK) group at UNSW.Epithelial thinning in ortho-k alone cannot explain AL shortening. Choroidal thickness changes may be a contributor because studies of the effects of optical appliances on the eye by Prof Earl Smith of the Texas-based University of Houston showed that plus lenses thickened the choroid while minus lenses thinned it.In an assessment of the eyes of seven- to 17-year-old subjects, ortho-k was found to have the greatest effect on the choroid tporally (a thickening) while the nasal sector thinned. The results were influenced by the optic nerve head and the optic nerve itself. At weeks one and three of the study, Dr Chen reported an overall thickening of the choroid of some 21 μm, which led to a diminished AL. The central choroid thickened by about 80 μm (some up to 100 μm).Overall, 49% of subjects experienced an AL shortening but the results were subject to diurnal variation, albeit at variations greater than those experienced by non-ortho-k subjects.Describing some pitfalls surrounding the use of AL data as a proxy for myopia progression rates and refractive error, Dr Chen started with the assumption that a slow AL change was indicative of low myopia progression. He suggested that AL change overestimated the level of control achieved.In addition, he said AL changes were not a proxy for myopic progression. From ophthalmoscopy, it is known that 1 mm at the fovea is about a 2.5 D change in the Rekoss disc lens of a direct ophthalmoscope. However, high myopes exhibit up to 0.6 mm increases in AL per annum (lesser myopes about 0.25 mm per annum), which does not translate to a myopic increase of 1.5 D per annum (high myope [0.6 D x 2.5 D]) or 0.63 D per annum for lesser myopic errors (0.25 D x 2.5 D).Confounding the results are normal age changes (eg, the cornea flattens, the crystalline lens thickens, and the anterior chamber deepens). It is also possible for myopia to progress and the AL to shorten. Corneal topography changes might offer a partial explanation but epithelial thinning and choroidal thickening can also play a part.In parting, Dr Chen noted that currently, we have little grasp of the contributions made by other optical components of the eye to myopia.

KEYNOTE SPEAKERS

John MountfordZhi ChenJohn PhillipsPaul Gifford

PULLING IT ALL TOGETHERDr John Phillips – a senior lecturer at the University of Auckland’s School of Optometry and Vision Science in New Zealand, long-time myopia researcher, and holder of an anti-myopia CL patent – tackled the subjects of myopia, choroidal thickness, and ortho-k.He confirmed that hyperopic defocus decreases choroidal thickness and promotes AL elongation while, conversely, myopic defocus thickens the choroid and inhibits AL elongation. He summarised the three factors affecting myopia as: environment; the eye’s optics, including optical interventions; and the retina. The latter is affected by pharmacological agents such as atropine acting on the RPE, the choroid, and the sclera.In a paper of which Dr Phillips is a co-author (Chiang et al., 2015), it was shown that retinal defocus can affect the choroidal thickness under the fovea by 5–8%. Thickness increased rapidly within 10 minutes of exposure to 2 D of myopic defocus but when a 2 D hyperopic defocus was attpted instead, the thickness decreases measured were slower to respond. No difference was found between myopic and metropic eyes subjected to the same treatment. Changes out to 60 minutes were measured.In a related study, atropine (0.3% applied nightly for up to six months) was found to block the choroidal response to hyperopic defocus (ie, there was no corresponding choroidal thinning). At the one-week mark, the study also showed a 5–10% increase in choroidal thickness from the baseline value. It was concluded that atropine acts on the choroid, the retina, or both.By mechanisms not understood, atropine appears to detect and block hyperopic defocus. Whether the mechanism is at the detection, transmission, or reception stage – or some combination of these factors – rains unknown. Any lag of accommodation at near also ses to be blocked whereas any lead of accommodation is not affected.Turning to myopia control in ortho-k, Dr Phillips noted that up to a 40% reduction can be realised in the first few years but longer term studies show that that level of reduction cannot be sustained, leading to over-estimations of efficacy and exaggerated claims. Referring to dual-focus CLs such as he has patented, he claimed they offer similar albeit slightly lower efficacy to ortho-k CLs but with much greater ease. Multifocal ortho-k (MOK) CLs were also mentioned as an option.Using MOK CLs monocularly (with a standard ortho-k CL in the other eye) on 30 children aged between 10 and 14 years who were progressing by at least 0.5 D per annum and whose Rxs were within -1.5 and -4 resulted in an almost immediate and sustained increase in choroidal thickness (10–15 μm) in the MOK-wearing eye. This was sustained out to 18 months. The ortho-k-wearing eye showed a thinning of between 5 μm (later) and 10 μm (earlier).Dr Phillips concluded that ortho-k prevents any abnormal elongation of the eye and MOK and ortho-k decrease myopia progression in the short term by 40–45%. He believed there was still the potential to increase the efficacy of both MOK and ortho-k treatments and that the combination of atropine and optical methods offered further hope of better outcomes.PREDICTING MYOPIA RISKBrisbane-based ortho-K and myopia researcher Dr Paul Gifford opened his presentation with figures relating to risk of various ocular pathologies in high myopia, including cataract (5.5X), retinal detachment (21.5X), and MMD (40.6X). Disturbingly, MMD is increasingly being seen in younger patients.Commencing a discussion on the ways of dealing with the increasing prevalence of myopia, Dr Gifford stated that single-vision spectacles are the worst possible way of dealing with the condition. Single-vision CLs are probably not much better, a statent supported by various studies over several years. Progressive power lenses, be they spectacles or CLs, are probably marginally better.Given that myopia control CLs such as CooperVision’s MiSight are scheduled to be launched into the Australian market and ortho-k therapy is now well established, it appears that the excuses for doing nothing are disappearing progressively. However, the lack of concrete recommendations from authorities, organisations, or researchers is probably a reflection of the lack of general agreent on just what should be done under each circumstance. About the only general agreent that exists currently is that outdoor activity is essential.Paradoxically, while seingly a simple issue, making practicable and effective changes are proving to be a significant obstacle. The Brisbane practice with which Dr Gifford is associated has been pursuing myopia control for more than 10 years. Patients have donstrated a liking and enthusiasm for being involved in their own care and the practice has expanded its patient numbers largely through word-of-mouth. An explanation of the risks and benefits is also usually appreciated. In that 10-year timeframe, one case of microbial keratitis occurred and no vision was lost.THE NORTH AMERICANS STRUT THEIR STUFFAssociate Professor Pat Caroline of Pacific University in Oregon, US delivered three lectures at the congress. One was a tag-team presentation with Canadian topography guru Mr Randy Kojima, who also teaches at Pacific University.Assoc Prof Caroline opened with what he termed the “miracle” of ortho-k – the fact that most change in Rx is achieved on the first night of wearing ortho-k CLs. The stage has now been reached whereby first-pair ortho-k success is usually achieved.He condensed ortho-k down to the “creation of a minus-powered correcting lens made of human epithelium” – the patient’s own epithelium. The process was described as pushing at the corneal apex and pulling on the epithelium in the reverse curve, with that process powered in part by a heart-driven, pulsatile pump.Mr Kojima opened with a discussion about astigmatism – was it limbus-to-limbus or was it more central? In a separate lecture, Dr Mountford noted that while uncommon, limbus-to-limbus astigmatism made for poor ortho-k success and the opposite effect to that desired could result.Generally, peripheral astigmatism is less than central astigmatism and can even be spherical, or almost so. Peripheral astigmatism is key to achieving a circumferential seal around an ortho-k CL and failure to do so can affect the efficacy of the pulsatile pump. For example, 1.37 D cyl results in a 38 μm height difference between meridians, well above the threshold of 25 μm for considering a toric CL periphery to avoid peripheral seal failure. Even spherical corneas can have small local height differences.Given that an ortho-k CL’s reverse curve zone extends to about 8 mm in diameter, CL alignment with the cornea beyond that is required if effective sealing is to be realised. Due to factors like these, Dr Mountford, Assoc Prof Caroline, Mr Kojima, and others believe that individualised ortho-k CL design is the future of the specialty.Mr Kojima noted that differences between CLs for adults and adolescents are significant enough to reduce success rates by 50% when ployed incorrectly. Furthermore, ortho-k CLs intended for myopia control generally use a smaller treatment zone (5–5.5 mm diameter) than adult versions (7 mm diameter) because young wearers need a more radical and aggressive approach to be successful.In a significant departure from conventional approaches, Assoc Prof Caroline raised the prospect of brief, open-eye ortho-k treatment (eg, one hour daily) as opposed to the more usual overnight CL wear. Studies have shown that 2 D changes can be achieved in neophyte wearers from one-hour treatment sessions. However, only a SCL can provide the 360° sealing, anterior eye conformance, and lid pressures required in the open-eye situation, which raises the possibility of using hybrid CLs specialised for the task.

KEYNOTE SPEAKERS

Pat CarolineRandy KojimaKate GiffordHelen Swarbrick

BINOCULAR VISION AND ORTHO-KMs Kate Gifford, a recipient of an OSO research scholarship, updated delegates on her endeavours. While pursuing a reduction in myopia and myopia control are the aims of ortho-k, it is important that visual comfort and normal binocular function are maintained.Each method of myopia reduction has different effects on visual functions. For example:

  • Atropine, with a 30–77% efficacy, affects accommodation – and therefore binocular vision (BV) – and pupil size
  • Gas permeable CLs and SCLs only have a 0–5% effect on reducing myopia but alter binocular vision the least
  • Bifocal, multifocal, and progressive power CLs have 29–70% efficacy and affect BV
  • Ortho-k has 32–100% efficacy and also alters the BV status quo.

However, not all cases are equal and when progressive power spectacles are used in a sub-group that exhibit esophoria and accommodative lag, the level of myopia control rises from 12–17% (for all myopes) to 37% with that particular group. Bifocal spectacles worn by progressive myopes can be 37–55% effective.Ms Gifford surmised that ortho-k and multifocal CLs reduced accommodative lag. She observed that BV matters because esophoria reduces reading accuracy, reduced vergence facility reduces reading speed and necessitates more eye movent, and the normal classroom now devotes 58% of class time to the use of digital devices. Those devices result in continuous near fixation of around 23-minute duration and other activities result in distance-to-near fixation changes at up to 10X per minute.The base-in help that minus spectacle lenses provide the wearer compound comparisons between spectacles and CLs used in particular circumstances. A confounding factor is the peripheral add provided by an ortho-k CL’s reverse curve that is significantly greater than that provided by multifocal/progressive SCLs, meaning that ortho-k’s myopic defocus is greater.Ms Gifford also showed that ortho-k increases positive spherical aberration, which increases depth of focus. Given myopia increases optical aberrations at near with a resulting decrease in image quality, she described myopes as having inaccurate BV behaviour.After outlining some of the clinical studies she had undertaken, Ms Gifford concluded that ortho-k reduces near esophoria, increases divergent (base-in) fusional reserves, reduces accommodative lag, and improves positive relative accommodation.ORTHO-K CONTROVERSIESLeading ortho-k researcher and acadic Prof Swarbrick discussed the evergreen issue of just what ortho-k is doing to the eye. Claims still circulate that in addition to the donstrable thinning and reshaping of the corneal epithelium, ortho-k also involves changes to the corneal stroma, corneal bending, and/or has other effects.Effects on the epithelium are rapid, reversible, and involve the anterior cornea only, leaving the all-important endothelium unaffected. On the downside, epithelial thinning has the potential to reduce the key barrier effect the layer affords the cornea against microbial infection, and by their very nature, changes to the epithelium cannot be permanent.Research has shown that the stroma can be somewhat affected under the reverse curve zone. Although early research used optical pachymetry, more recent research – including that in the ROK group – uses anterior segment OCT. Recent research confirms earlier work by Alharbi and Swarbrick (2003) that the stroma undergoes about a 5 μm (≈1%) thickening due to hypoxia while the epithelium thins centrally and thickens mid-peripherally.The question arose as to why some studies failed to donstrate epithelial thinning, which led some authors to revert to the corneal bending explanation. A common the turned out to be the use of a particular ultrasonic corneal thickness gauge – the SonoGage Corneo-gage Plus pachymeter.Prof Swarbrick’s group donstrated that, at thicknesses <60 μm, the SonoGage technology was incapable of accurate information and was useless at <48 μm. As the epithelium has a normal thickness before ortho-k therapy of about 50 μm (50–55 μm), the source of the recurring errors became clear.After almost two decades of ongoing research, Prof Swarbrick said the ROK group was happy to attribute the primary ortho-k effect to central corneal epithelial thinning only.Controversy? What controversy?THE NEXT OSO CONGRESSThe OSO has settled on holding its congresses every two years to mirror the likely pace of new developments and novel research findings and to ensure that the overlap between the information conveyed at consecutive gatherings does not lead to new information underload. Given the large attendance at the 2016 event, mbers of the 2018 OSO congress organising committee have their work cut out for th.


REFERENCESAlharbi A, Swarbrick HA, 2003. <>The effects of overnight orthokeratology lens wear on corneal thickness. IOVS. 44(6): 2518 – 2523.Chiang ST et al., 2015. <>Effect of retinal image defocus on the thickness of the human choroid. Ophthalmic Physiol Opt. 35(4): 405 – 413.Hiraoka T et al., 2012.<> Long-term effect of overnight orthokeratology on axial length elongation in childhood myopia: a 5-year follow-up study. IOVS. 53(7): 3913 – 3919.