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HomemiophthalmologyMyopia ‘A to Z’: Existing and Future Treatments

Myopia ‘A to Z’: Existing and Future Treatments

The prevalence of myopia is progressing faster than predicted, and for reasons that remain largely unknown.1 Myopia impacts work productivity, educational achievement, and health costs. Individuals, parents and governments are increasingly concerned about the “epidemic” of myopia.

As a myope myself and a beneficiary of refractive surgery, it has been exciting to see refractive surgery increasingly become mainstream, both professionally and in the public perception.

Established procedures such as LASIK and surface ablation represent the majority of vision correction procedures completed across the world and have provided patients with the opportunity to reduce their dependence on optical aids and improve their quality of life.2 However, many alternatives exist.

Acupuncture

Acupuncture has been increasingly integrated into general health care. Accordingly, complementary health journals have suggested a role in the delay of myopia. The evidence however remains mixed at best. A Cochrane Database review in 2011, to address the safety and effectiveness of the acupuncture in children, found only two randomised controlled trials (RCTs), both with limited numbers and short follow up.3 Both trials reported that patients experienced mild pain during the acupuncture stimulation. The reviewers suggested further RCTs prior to any recommendations. Additional trials have been undertaken since this initial review, however results have yet to be published, suggesting that consistent benefits may not be readily achievable.4,5

Clear Lens Extraction


Figure 1. Clear lens extraction with multifocal IOL (Panoptix)

The use of clear lens extraction (CLE) as a refractive modality has increased in recent years comparative to LASIK and surface ablations.6 CLE presents several potential advantages over corneal ablation techniques namely; the treatment of higher degrees of refractive error, the ability to address presbyopia with multifocal or accommodating intraocular lenses and the obviation of cataract surgery at a later date.7 Not surprisingly, CLE candidates are often younger and more myopic than the standard cataract cohort.8 The risk of retinal detachment remains a consideration in high myopes. In a comparative study of patients undergoing either CLE or phakic intraocular lenses, approximately 5 per cent of eyes undergoing CLE resulted in retinal detachment requiring further surgery compared to no eyes in the Phakic IOL cohort. Against this finding however, the preoperative spherical equivalent was significantly higher in the CLE group (-16.7D vs. -13.6D).9 More recently, an additional comparison highlighted the reduced likelihood of secondary intervention for CLE patients compared to Phakic IOL implantation.10

Although multifocal IOLs represent an option for CLE patients, myopes may not represent the optimal candidates for these lenses due to pre-existing high demands for clear unaided near vision. The decision to proceed will be individually based on assessment of practical needs and personality.

Diet

Duke-Elder, in his original treatise on myopia some 80 years ago, suggested excessive near work, bad ocular hygiene and physical debility in the early years of growth as accessory risk factors to the progression of myopia. His work was prescient in many, but not all, ways.11 The influence of diet on myopia remains unclear although studies relate high vitamin D serum levels to low refractive error.12 Increasingly, evidence suggests the positive role of outdoor play rather than dietary concerns, however further research may reveal the use of vitamins as an adjunct.

Contact Lenses

The evidence for the reduction in myopia progression by using bifocal or progressive multifocal contact lenses remains relatively promising. A recent Australian based RCT described greater control over myopia progression and axial elongation compared with previous trials.13 A network meta-analysis of various interventions for myopia control in children suggested similar efficacy in the review of existing trials.14 Understanding the contributions of relative peripheral refraction, binocular visual function and higher-order aberrations; that may represent some of the mechanisms underlying this effect remains key to developing a consistent, long-term treatment.15 We await further studies in this area.

LASIK

LASIK represents the most frequently performed refractive procedure across most countries.6,16 Analysis is now available highlighting the long-term efficacy of the procedure. Alio et al describe a small sample with preoperative myopia between -6D and -18D at 15 years following surgery. The authors show a safety index of 1.23 and efficacy index of 0.95, indicating excellent outcomes over this extended follow-up period. Progression was detected over time in some patients, with low preoperative pachymetry and residual stromal bed the remaining predictors of keratometry change.17 This likely represents a combination of older technology and perhaps out-dated patient selection with the treatment of extreme myopes.

Our awareness of potential risk factors has been continually refined, as has technology to detect the presence of ocular conditions, such as keratoconus, which may affect outcomes. A list of relative and definite contraindications for all main refractive techniques is listed in Table 1.

(Click here to view Table 1)

Mydriatics

Pharmacologic interventions, such as atropine and pirenzepine have been shown effective in reducing myopic progression.14 The acceptability of treatment has remained a concern due to the extended accommodative paresis and mydriasis necessitating the use of bifocal glasses.18 Photophobia remains a further issue. Polling et al noted that 72 per cent of patients reported significant photophobia.19 Titration of the drop strength has been shown to increase general tolerability without serious adverse effects.18

MyoRing


Figure 2. MyoRing intrastromal insert (insitu)

MyoRing is a 360° continuous full-ring implant that is placed within a corneal pocket at approximately 300 microns depth. Although the literature leans towards a niche role in improving overall corneal geometry for patients with keratoconus, the company promotes the ability to correct myopia up to -16D. The technique is described in a single paper in JCRS from 2008 however no further evidence is yet offered suggesting little, if any, uptake in this technology for myopia.

Orthokeratology


Figure 3. Ortho-K Contact Lens

Ortho-K, recently perceived as the most effective method of myopia control, continues to garnish a place in optometry.20 The relative safety of the procedure is sound albeit requiring a combination of proper lens fitting and rigorous compliance to a lens care regimen.21,22 Myopic control varies between studies, however a recent meta-analysis states that up to 41 per cent of patients retained effect at 24 months.23 Of interest, Li et al suggest that Asian patients may receive a greater effect compared to Caucasian patients.24 Further well-controlled trials are required to confirm this hypothesis however.

Perceptual Learning

Researchers have investigated improving performance in visual tasks with practice for many years. The majority of studies represent a combination of behavioural and brain-stimulation treatments incorporating both passive and interactive techniques.25 Suggested for mild myopia up to around -2D, studies have shown mid-term improvements in uncorrected vision and contrast sensitivity.26, 27 Importantly, no studies have indicated significant refractive changes, suggesting a minor role at best. Anecdotal evidence of post-refractive benefits to improve unaided vision has been presented.

Phakic IOL


Figure 4. Phakic IOLs (Left: Implantable contact lens, Right: Verisys anterior clip-on phakic IOL)

Phakic IOLs have long been demonstrated to provide effective, predictable and stable refractive outcomes for predominantly moderate to high ranges of myopia.28 Meta-analysis suggests a definite benefit over ablative techniques in higher errors in terms of best-corrected visual acuity and contrast sensitivity.29 Against this is the elevated risk of cataract formation or exaggerated endothelial cell loss depending on the location and type of implant.30 More recently, phakic IOLs have found additional use in conjunction with surface ablation and cross-linking to correct ammetropia related to keratoconus.31 The combination of excellent results obtained by laser refractive techniques and local population demographics has reduced the penetration of Phakic IOLs across the refractive landscape, however, they remain an excellent option for the appropriate candidate.

Photorefractive Instrastromal Cross-Linking

Performed in conjunction with LASIK, accelerated or “flash” cross-linking is promoted to further enhance post-surgery corneal biomechanical integrity. This procedure has gained some acceptance within refractive surgery albeit an adherence to strict screening protocols continues to provide the most safety for potential patients.

Recently, a standalone cross-linking procedure has been proposed to offer a non-surgical refractive correction. The potential dual benefits of this procedure would be the strengthening of the cornea and restoration of biomechanical stability. The procedure is completed according to current cross-linking protocols with the addition of a topographic guided UV light source. It is expected that this technique will benefit patients with low levels of primary myopia or those with residual myopia following cataract or refractive surgery. As of mid-2016, no current peer-reviewed publications are currently available to indicate potential results. (Refer Figure 5)

Posterior Scleral Reinforcement

Scleral reinforcement is generally considered only once conventional therapy avenues have been exhausted. The surgery involves using additional tissue such as donor sclera to effectively encircle the eye, preventing further progression by providing additional support for the increasingly thin posterior pole. Contralateral eye and cohort studies have shown Posterior Scleral Reinforcement to statistically reduce, but not halt, axial length elongation.32,33 Safety reports suggest, in experienced hands, it is a reliable procedure, however, significant complications, including cilioretinal artery occlusion, have occurred.34,35 Despite the relative safety profile, both the use and timing of the procedure remain somewhat controversial.

Radial Keratotomy


Figure 5. Topographic collagen cross-linking unit (Avedro)

Radial Keratotomy (RK) remains a largely historical procedure, however, prior patients continue to remain a professional concern. A significant proportion of patients subsequently developed hyperopic shift and irregular corneas following surgery.36 This impacts future surgical considerations, including cataract surgery through the calculation of lens power and the choice of lens type. Although the use of multifocal IOLs in post-RK patients has been described, the risk of significant phenomena is increased.37 Safety concerns also remain with long-term patients at risk for traumatic rupture and visual fluctuation, particularly at high altitude.38,39

Scleral Cross-linking

The use of chemical crosslinking to increase the biomechanical rigidity of the sclera in cases of progressive myopia remains limited to animal research.40 In theory, a subsection of sclera is treated in broadly similar terms to corneal cross-linking. Animal models suggest a significant increase in scleral strength without corresponding retinal penetration or side effects at follow-up.40-42 This treatment has potential to replace surgical strengthening procedures but remains limited until standard access and safety profiles have been established.

Small Incision Lenticule Extraction


Figure 6. SMILE refractive laser and lenticule removal

Small Incision Lenticule Extraction (SMILE) represents the most recent clinical addition to refractive surgery. The femtosecond laser is used to create an intrastromal lenticule, which is manually removed through a small peripheral incision. Patient selection, as with all refractive surgery, remains critical. Most standard parameters are similar to LASIK, however, as results propose SMILE maintaining more predictable and greater cohesive tensile strength post-surgery compared to both LASIK and surface ablation, the potential range of refractive errors and corneal thickness treated may be broader.43,44 This is what we have seen in clinical practice. The absence of a corneal flap removes the risk of related concerns, however, potential postoperative complications still exist including epithelial ingrowth, diffuse lamellar keratitis, irregular astigmatism and mild dry eye.45 Ectasia has been reported, however, keratoconus had previously been diagnosed confirming this as both the likely cause and as a primary contra-indication for surgery.

Refractive comparisons suggest that SMILE provides equivalent refractive outcomes compared to LASIK and surface ablation, if not exceeding these in high myopia.46,47 Higher order aberrations are reduced in comparison to LASIK, which may suggest greater potential for postoperative quality of vision albeit literature results remain variable.47,48 Despite studies showing less physiological change immediately following SMILE compared to LASIK, visual recovery is often described as taking slightly longer than LASIK. Refinements in laser energy and surgical techniques have reduced this difference, however. Until recently, postoperative residual myopia was treated with surface ablation over the SMILE cornea. Surgeons have been provided the option of creating a LASIK-like flap using the original SMILE parameters. This allows the surgeon to then lift the flap and proceed to ‘standard’ laser ablation. Early results of this technique (CIRCLE) have been promising.49

Stem Cell Therapy

The therapeutic use of stem cells was initially proposed as a strategy to restore function to damaged tissues. More recently, however, research has developed to include both modulatory and trophic support.50,51 A target in relation to myopia, and similar to scleral cross-linking, is to use stem cell therapy to provide additional strength or reinforcement to the oft-weakened myopic sclera.50

Growing evidence suggests a link between dopamine and the development of myopia. Direct intravitreal injection of dopamine or the transplant of stem cells engineered to produce dopamine may provide an additional avenue for the future treatment of myopia progression. Early animal trials have provided the basis for further trials, however this treatment remains largely theoretical.

Surface Ablation


Refractive treatment ranges

Surface ablation techniques (ASLA, LASEK, Thin-flap LASIK, PRK) have evolved considerably and demand a consistent place within refractive surgery. The various techniques differ largely in terms of the preparation of the corneal epithelium and the use of adjunctive mitomycin. Safety and refractive outcomes however, appear to be mostly consistent amongst surface techniques.52-54 Sia and co-authors found that PRK with mitomycin showed some benefits in minimising corneal haze formation, however there was no discernible difference in the postoperative refractive outcomes between separate surface laser surgeries.55

Patients with relatively thin corneas, subtle corneal irregularities and mild dry eye, that is those that remain unsuitable for the LASIK procedure, form the majority of patients that may undergo surface ablation.56 Surface ablation patients require counselling regarding the extended follow-up and slower visual recovery compared to other laser refractive techniques. Postoperative comfort and visual recovery is aided by the use of postoperative bandage contact lenses, (refer Table).

Summary

The treatment of myopia is one of the biggest challenges for eye-care professionals. Many technologies will emerge and it is our responsibility to guide our patients in choosing the best option depending on the circumstances. Open and professional collaboration between orthoptists, optometrists and ophthalmologists will see our patients benefit from a range of different skill sets, expertise and myopia treatment options.

Dr. Colin Chan MBBS (Hons), FRANZCO is an ophthalmic surgeon and Head of Refractive SIG at Vision Eye institute. He is a Senior Clinical Lecturer at the University of Sydney and a Director of the Refractive Surgery Degree at University of Sydney.

Christopher Hodge BAppSc (Orth), PhD is a Clinical Research Coordinator with Vision Eye Institute and an invited lecturer for the Masters of Refractive Surgery program at University of Sydney. An experienced orthoptist and orthoptic team leader, he completed a Doctor of Philosophy in Ophthalmology and Eye Health at University of Sydney in 2015.

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