At the completion of this article, the reader should be able to improve their myopia management care. Including:
- Know the systemic conditions related to high myopia
- Develop a clinical evaluation protocol for high myopia
- Know the pathological complications associated with high myopia
- Understand the elevated risk of sight-threatening complications in myopic patients
As the consequences of myopia rise globally, high myopia retinal complications will only become more common. Optometrists will increasingly be called upon to provide the solutions, explanations and education to a growing number of patients in search of answers.
Brian Peng
MClinOptom BVisSc
Clinical optometrist – private practice
Clinical educator – Myopia Profile Pty Ltd
Dr Kate Gifford
PhD BAppSc(Optom)Hons GradCertOcTher.
FBCLA FIACLE FCCLSA FAAO GAICD
Optometrist, professional educator and clinician-scientist
Co-founder and lead educator – Myopia Profile Pty Ltd
The International Myopia Institute (IMI) defined myopia where the spherical equivalent refraction of an eye is ≤ -0.50 D. High myopia is defined as an eye with spherical equivalent refraction of at least -5.00D or -6.00 D, depending on clinical or research settings.
Historically, low and moderate myopia were termed ‘physiologic,’ but in 2019 the IMI asserted that the terminology of ‘physiologic myopia’ was misleading, as myopia cannot be implied to be “devoid of any adverse consequence”. Similarly, high myopia and pathologic myopia are not synonymous, as the latter is defined by structural complications in the posterior segment which are related to excessive axial elongation, not necessarily to a dioptric threshold.1
The prevalence of myopia and high myopia has dramatically increased worldwide,2-4 particularly in countries within East Asia such as China,5 Japan,6 Singapore,7 and South Korea8 where myopia prevalence is already high. It has been projected that almost five billion individuals of the world’s population will suffer from myopia by 2050, with almost one billion people suffering high myopia.9
Myopia is an emergent public health concern, and a large body of evidence now points to the necessity of prescribing interventions to slow myopia progression in suitable patients. The World Council of Optometry affirmed this position in mid-2021, indicating that eyecare practitioners (ECPs) worldwide must work to increase awareness and ensure effective myopia management strategies are implemented to achieve better patient and public health outcomes.10
High myopia in children
High myopia in young children is a red flag for systemic complications. Examples include connective tissue disorders such as Stickler syndrome and Marfan syndrome, and developmental syndromes such as Noonan and Down syndrome. A retrospective study of children under 10 years of age with myopia ≤ -6.00 D showed only 8% had ‘simple high myopia’ without other ocular or systemic associations, while 54% of children had an underlying systemic condition.11
These children require referral to, or co-management with ophthalmology. Accurate and early diagnosis facilitates educational planning, and provides the patient and their family with an understanding of the condition and its consequences.11 Furthermore, diagnosis of a heritable ocular or systemic condition may encourage the screening of the condition in other family members.
A simple approach may be to initiate referral and/or co-management with a paediatric ophthalmologist for:
• Children under age 10 with high myopia who have not yet seen an ophthalmologist
• Children whose dioptres of myopia exceeds their age in years
• Where referral and/or co-management is necessary for strabismus, amblyopia, or ocular disease findings.
Clinical evaluation
Evaluation of visual function in patients with myopia involves measurement of distance and near visual acuity, subjective and/or objective refraction, and evaluation of binocular and accommodative function.12 The IMI defines myopia as ‘when ocular accommodation is relaxed1 which points towards cycloplegic assessment where possible and available. Cycloplegic refraction is a necessity in research studies, and undertaking the same in clinical practice allows for maximum accuracy; however it is not a necessity as both cycloplegic and standard clinical techniques can control accommodation. For example, non-cycloplegic retinoscopy in children with contralateral fogging of +6.00D yields results within 0.25D of cycloplegic testing.13
Structural assessment of myopic eyes should include anterior eye health slit-lamp assessment, intraocular pressure measurement, corneal topography (on indication), axial length measurement (where available), fundus examination and imaging.12 Measurement of axial length can be integral in measuring progression in younger myopes, and identifying risk of pathologic myopia in patients of all ages.
Axial lengths exceeding 26 mm show correlation with escalating risk of pathology and eventual vision impairment.14 Regardless of the refractive level of myopia, patients of all ages with axial lengths approaching this value are also reasonably defined with ‘high myopia’ from the point of view of their additional clinical care requirements.12
Pathological complications
High myopia is associated with various pathological findings, particularly those manifesting in the posterior segment. ‘Pathologic myopia’ refers to the structural changes in the posterior eye as a result of excessive axial elongation, such as posterior staphyloma, myopic maculopathy and optic neuropathy.15 While most pathologic myopia occurs in eyes with high myopia by refractive definition, individuals with low or moderate myopia can also suffer pathological sequelae. Numerous studies in adult or elderly populations have shown that around half of adults with high myopia are likely to develop pathologic myopia.15
Myopic Maculopathy
Myopic maculopathy is one of the most prevalent disease complications observed in high myopia. It is characterised by slowly progressive retinal pigment epithelial (RPE) and chorioretinal atrophy, and sometimes accompanied by choroidal neovascularisation (CNV), lacquer cracks or Fuchs spot. Macular retinoschisis, lamellar macular hole and foveal retinal detachment are other potential complications. The META-PM Classification of Myopic Maculopathy provides a simple five category system (Figure 1 and Table 1).
Myopic maculopathy is one of the leading causes of blindness in several countries around the world, including China, Ireland, Israel, Japan and the United Kingdom.16-20 The Blue Mountains Eye Study in Australia reported the overall prevalence of myopic retinopathy in 1.2% of the population.21 However, prevalence increased dramatically to over 50% for myopes ≤ -9.00 D compared to 0.42% of myopes < -5.00 D, representing a 60-fold increase in risk of myopic retinopathy.
Sadly, atrophic forms of myopic maculopathy are untreatable. At best, the established first-line treatment for secondary myopic CNV is intravitreal anti-VEGF therapy.15
Rhegmatogenous retinal detachment (RRD)
Rhegmatogenous retinal detachment (RRD) is another potential sight-threatening complication of myopia, with an incidence estimated to be between 6.3 and 17.9 per 100,000 individuals.22 RRD arises when fluid from the vitreous cavity enters via full-thickness retinal defect into the subretinal space, inducing a separation of the neurosensory retina from the underlying RPE.
RRD may occur in non-myopic eyes, but as the Eye Disease Case-Control Study in the US suggested, a substantial proportion (55%) of idiopathic RRD cases can be retraced to myopia.23 The risk of developing retinal detachment increases significantly with severity of myopia and greater axial length.
Compared with non-myopic eyes, lower levels of myopia (up to 3.00 D) attract a four-fold increased risk of RRD; while higher levels of myopia have an eight to 10-fold increased risk of detachment.22,24 Numerous studies have also found eyes with axial length > 26 mm had a significantly elevated risk of RRD in both phakic and pseudophakic patients.25,26 The intrinsic risk may be related to the architecture of myopic eyes, which are more likely to have a thinner retina and a predisposition to premature vitreous liquefaction and subsequent posterior vitreous detachment.27,28
Primary Open Angle Glaucoma
Many studies have implicated an association between myopia and primary open angle glaucoma (POAG), increasing with degree of myopia. The Blue Mountains Eye Study reported a relationship between glaucoma and low myopia (odds ratio (OR) 2.3) as well as moderate-to-high myopia (OR 3.3).29 This was maintained in a recent meta-analysis which found those with moderate-to-high myopia (OR 2.46) and low myopia (OR 1.65) have an increased risk of developing open-angle glaucoma.30
The pathogenesis of POAG itself is still poorly understood, let alone the link between myopia and POAG. Accuracy of diagnosis is complicated by the fact that retinal nerve fiber layer (RNFL) thinning is characteristic of both myopic structure-function changes as well as ‘true’ glaucomatous optic neuropathy.31 The prevailing theory is that highly myopic eyes are more susceptible to optic nerve head damage by elevated intraocular pressure (IOP), which may be related to the structure and arrangement of connective tissues in the posterior segment.
Cataracts
High myopia is known to be associated with cataract development. The Blue Mountains Eye Study showed that early onset myopia (before 20 years of age) was strongly associated with posterior subcapsular cataract (PSC) (OR 3.9) and that hyperopia appeared to be protective of PSC (OR 0.6).32 Consistent with the conditions described above, a dose-dependent relationship was found; the risk of PSC is greater in high myopia (OR 5.5) than low myopia (OR 2.1). The aetiological link between myopia and cataract is unclear, although it has been suggested that incident cataract is more common in myopia due to the increased oxidative susceptibility of myopic crystalline lenses.33
Managing High Myopia
Ultimately, while myopia control options should be communicated to the patient and their family, managing expectations regarding their efficacy is equally important.
Spectacles
The first line of management for patients with high myopia is prescribing a refractive correction. For patients young and old with high myopia, control of vertex distance in both refraction and optical dispensing is crucial for best acuity. High myopes approaching 10 D and beyond can suffer reduced visual acuity34 and contrast sensitivity35 compared to lower myopes, and impaired quality-of-life similar to that of patients with keratoconus.34 Optimum vision can be achieved by measuring vertex distance in refraction, checking acuity in a trial frame, and then attempting to match this vertex distance with the spectacle frame. High index spectacle lens materials improve optical quality and cosmesis by minimising peripheral distortions in a thinner lens profile.
Contact lenses
Contact lenses can provide a superior correction option for paediatric and adult high myopes, overcoming the limitations of spectacles. Contact lenses may improve visual acuity compared to spectacles by reducing the minification effect caused by differences in vertex distance. Field of view is improved, and there are obvious aesthetic and functional advantages.
When fitting from spectacles to contact lenses, though, watch for any issues with near vision. High myopes have less accommodative and convergence demand in spectacles, compared to contact lenses, due to vertex distance and intrinsic prismatic effects. This can lead to asthenopic symptoms during near work in individuals with near exophoria, incipient presbyopia, or a habitually close working distance.36
Prescribing interventions to slow myopia progression in children and teens is important, and the long-term impact can also be significant. Reducing a patient’s final level of myopia by one diopter reduces the risk of myopic maculopathy by 40% regardless of the level of myopia.37 The evidence base for applications in high myopia is limited, though, as most studies include only participants with low-to-moderate myopia.
OrthoK
For high myopia, there is a small amount of evidence for myopia control efficacy with orthokeratology (orthoK) and low-concentration atropine. Conventionally, orthoK lenses have been used to treat low-to-moderate myopia, and fitting for high myopia may result in complications such as corneal staining and lens decentration.38
Partial orthoK correction may be useful. In one small study, myopes with between 6.00 and 8.00 D spherical equivalent underwent partial (4.00 D) correction of myopia in conjunction with single vision spectacle daytime wear for the residual refraction. This resulted in 63% reduction in axial elongation over two years,39 comparable with the efficacy of orthoK for control of low and moderate myopia.40
Atropine
Topical atropine has established myopia control efficacy for children from four up to 15 years of age. Among the lower concentrations, atropine 0.05% currently appears to provide the best balance of efficacy with minimal side effects, slowing axial elongation by around 50%.41 This is a similar efficacy to the best available spectacle and contact lens interventions.42
The landmark Low-Concentration Atropine for Myopia Progression (LAMP) study did not report specific outcomes for high myopia, but did not exclude them from the study criteria. As atropine alone does not provide visual correction of myopia, it is generally preferred as a first-line treatment where optical interventions (spectacle and contact lenses) are not available or suitable. This could be the case for high myopia, where there may be wider prescription availability in single-vision spectacles and contact lenses.
Atropine 0.01% can be combined with orthoK to increase short-term myopia control efficacy, but again this evidence is limited to those without high myopia.43 There is no other evidence at this stage for the efficacy of atropine combined with other optical interventions for those with any level of myopia.
It’s important to educate patients and any caregivers on the potentially sight-threatening conditions of myopia and that the risk is proportional to the severity of myopia. For patients with high myopia, of all ages, the IMI recommends annual retinal health examination through dilated pupils. Multimodal imaging such as fundus photography and optical coherence tomography (OCT) may be performed to document retinal abnormalities and changes. Patients and their families should be counselled on the symptoms of retinal break in order to recognise and appropriately respond to an ocular emergency.12
A careful approach
Clinical management of high myopia requires a careful approach in addressing both vision needs and ocular complication risk. In young patients with high myopia, systemic health associations must be investigated, and co-management between optometry and ophthalmology can be required.
Prescribing an appropriate optical correction should be prioritised to provide best possible vision. Patients– and their caregivers in the case of children – benefit from education on the importance of lifelong ocular health assessment needs, and in setting appropriate expectations for myopia control.
More reading
Managing myopia with spectacle lenses
Is two better than one? Combining treatments for myopia control
Axial length matters in myopia management
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