Myopia Decoded
In 2016, the Late Brien Holden and his colleagues published a paper that shook the eye care field across the world.?The paper concluded that by 2050, 50% of the world's population will be myopic, making myopia the leading cause of preventable visual impairment in the world.?In its World Report on Vision, the World Health Organisation recognises myopia to be one of the five conditions that are currently contributing to visual impairment across the globe.?Since then, eye care practitioners globally have shifted into fifth gear to tackle what is being lovingly referred to as 'The Myopia Epidemic'.?This series of articles will cover all the latest research in Myopia Management, including classification and risk factors of myopia, as well as the various myopia management strategies, their protocols and efficacy to help you choose the strategies most suitable for you to implement in your practice.
Definition and Classification of Myopia
The current World Health Organisation definition of myopia is as follows:
"A refractive error in which light rays entering the eye parallel to the optic axis are brought to focus in front of the retina when accommodation is relaxed.?This results from an overly curved cornea or from the eyeball being too long from front to back.?It is also called nearsightedness."
While the definition exists, and myopia has been acknowledged by WHO, to be a definite public health concern, there is no validated, universally recognised classification system for myopia, such as those that exist for Diabetic Retinopathy or Retinopathy of Prematurity.?Daniel Flitcroft and colleagues published a paper in 2018, proposing a system where myopia can be defined qualitatively, quantitatively and descriptively.?
Qualitative definitions:?The qualitative definitions refer to the physiological reason behind the development of myopia.?This is essential in determining the best strategies for monitoring the progression and managing myopia.
Axial Myopia: "a myopic refractive state that can be attributed to excessive axial elongation": Myopia as a result of a longer than average eye ball
Refractive Myopia: "a myopic refractive state that can be attributed to changes in the structure or location of the image forming structures of the eye": Myopia as a result of higher than average corneal curvature and/or higher than average power of the crystalline lens
Secondary Myopia: "a myopic refractive state for which a single, specific cause can be identified that is not a recognised population risk factor for myopia development": Myopia as a result of a specific underlying cause, which does not fall under the normal risk factors for the development of myopia; this may include an adverse drug event, a corneal abnormality or a systemic condition
Quantitative Definitions:?The quantitative definitions refer to the degree of myopia present.?This is necessary to assess the risk of further complications that may lead to visual impairment.?All of the below quantitative definitions refer to the spherical equivalent refractive error (sphere + 1/2 cylinder) of an eye, when ocular accommodation is relaxed.
Myopia:?Equal to or more than -0.50D
Low Myopia: -0.50D to (but not including) -6.00D
High Myopia:?Equal to or more than -6.00D
While we are all familiar with the terms 'Low Myopia' and 'High Myopia', the paper proposed an additional quantitative definition:
Pre-Myopia: +0.75D to (but not including) -0.50D "in children where a combination of baseline refraction, age, and other quantifiable risk factors provide a sufficient likelihood of the future development of myopia to merit preventative interventions":?According to the CLEERE Study, quantifiable risk factors may include accelerated axial elongation and low or no hyperopia in children compared to age-matched normative data.?Furthermore, other well- documented risk factors such as a positive family history of myopia and environmental factors such as time spent indoors or outdoors may also warrant intervention.
Descriptive Definitions:?The descriptive definitions refer to the complications caused as a result of a high degree of myopia with the absence of any other underlying condition.
Pathologic Myopia: This is an encompassing term, referring to pathology, which is a result of excessive axial elongation, resulting in deterioration of visual acuity, which may eventually lead to visual impairment.?Pathologic Myopia includes:
Risk Factors of Myopia Development and Progression
It is important to understand the risk factors of the development and progression of myopia in order to plan interventions, whether that involves advice on lifestyle and habits or exploring methods of myopia control.?It is well documented that there are both genetic and environmental factors that contribute to the development and progression of myopia and while there have been several suggested risk factors, there is strong evidence suggesting four risk factors that have a strong contribution to causality.?
As mentioned above, it is well documented that educational pressure does contribute to the development and progression of myopia, however, the reasons behind this are much debated.?Some studies have found a clear relationship between near work and the progression of myopia and arguably, children in school spend more time reading and writing, which could be a contributing factor. Initially it was suggested that the accommodative lag that was a result of continuous near work triggering myopic progression, but more recent animal studies have shown that hyperopic defocus stimulates axial elongation and myopic progression.
3.?Time Spent Outdoors:?Strong evidence has been produced supporting the fact that 40-80minutes of time spent outdoors significantly reduces the incidence of myopia.?This has been attributed to the increased production of dopamine due to exposure to bright light during time spent outdoors in the daytime, which appears to inhibit axial elongation.?Other studies have also shown that myopic children and teenagers exhibited reduced Vitamin D levels, which would be a result of lack of exposure to sunlight, therefore increasing the time spent outdoors, increased vitamin D levels and in turn should slow down the progression of myopia.?The exact mechanism of the relationship between time outdoors and myopia is yet to be fully understood, but it is clear and conclusive that this relationship exists.?Therefore, advising parents about adopting this lifestyle change is an integral part of myopia management.
4.?Axial Length (AL) and Spherical Equivalent Refraction (SER):?The Northern Ireland Childhood Errors of Refraction (NICER) Study and The Singapore Cohort of the Risk Factors for Myopia (SCORM) are two studies carried out at opposite ends of the globe.?NICER included a Western European White population, while SCORM included primarily East and South Asian populations.?The data from both NICER and SCORM was in agreement that the earlier the onset of a long AL and a myopic SER, the higher the rate of progression of myopia.?
The data from NICER and SCORM, as well as several other longitudinal studies, has enabled eye care practitioners to make logical predictions when it comes to the incidence and rate of progression of myopia.?With the data from the NICER Study, colleagues at Ulster University were able to create the Predicting Myopia Onset and Progression (PreMo) risk factor indicator
While PreMo is predominantly based on a white Western European population, the prevalence of myopia in the United Kingdom is not completely dissimilar to that of South Asian Urban populations, so it can certainly be used as a guideline for risk assessment and management strategies.
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What is Myopia Management?
As mentioned before, it has been predicted that half the global population will be myopic by 2050, therefore intervention is imminent.?Over the last 15 years, extensive research has been and continues to be carried out globally to find a plausible solution for the 'myopia epidemic'.?
Based on the myriad of evidence of the prevalence and progression of myopia, the World Council of Optometry published a resolution for the "Standard of Care for Myopia Management by Optometrists" .?This implies that some form of myopia management is now considered the duty of care by the optometrist to their patient, where it would be considered negligent if myopia management is not provided when appropriate.
Myopia management is a proactive decision by the practitioner to take action to slow down the progression of myopia using evidence-based and clinically proven interventions.?This does not include simple correction of myopia with spectacle lenses or contact lenses to improve the visual acuity.?There is strong evidence to suggest that merely correcting the myopia WILL NOT slow down the progression. Furthermore, there appears to be a misconception among parents that their child should be slightly under-corrected to avoid myopia progression, however, there is no evidence to back this up, on the contrary, there is strong evidence that suggests that under-correction actually increases the rate of progression and is therefore contraindicated in myopic children.?According to the International Myopia Institute publications, a clinically significant reduction in progression is 50%.
Interventions
The goal of myopia management is to reduce the progression of myopia and there is decades worth of conclusive evidence demonstrating that axial elongation is the key factor in the progression of myopia, hence reducing axial elongation is the best strategy for reducing the progression of myopia.?All of the interventions are designed around this strategy and there is now strong evidence to suggest that multiple interventions implemented simultaneously can be more effective in cases where the myopia progression is aggressive, for example, in children where the onset of myopia is at an early age.?The interventions fall into three categories: optical, pharmaceutical and environmental / behavioural.?We will be discussing the principle, efficacy, safety and implementation of all of the aforementioned interventions.
Pharmaceutical Interventions
Principle:?Pharmaceutical interventions for slowing down the progression of myopia have been in place for some years.?The pharmaceutical agent most commonly used is Atropine.?Atropine is a broad-spectrum anti-muscarinic agent, which blocks muscarinic acetylcholine receptors in smooth ocular muscle with parasympathetic innervation.?This results in cycloplegia (total relaxation of accommodation) and mydriasis (pupil dilation).?The initial reasoning behind using atropine for myopia control was due to the belief that relaxing accommodation reduces axial elongation and the positive efficacy of the drug was a result of cycloplegia.?However, recent animal studies have shown that this is not the case and in actuality, it is a possible effect of the atropine mainly on retina and the sclera that reduces axial elongation, with some contributing factors from the retinal pigment epithelium and the choroid.?Atropine may increase the dopamine production in the retina and dopamine agonists inhibit myopia progression. At the level of the sclera, animal studies have suggested that atropine increases the thickness of the scleral fibrous layer in myopic eyes, reducing axial elongation.
Efficacy:?Most literature agrees that atropine is the most effective intervention in reducing myopia progression, ranging from a 70% to 12% reduction in progression depending on the dose, with higher doses demonstrating a greater reduction.?The LAMP study, published recently, investigated to efficacy of low dose atropine: 0.05%, 0.025% and 0.01%.?The outcome was a clinically significant reduction in myopic progression, with virtually no side effects after 24 months.
Safety:?Conventional doses of atropine used for diagnostic purposes have short side effects such as blurred vision, glare and photophobia and long term exposure to excessive amounts of UV radiation, all of which can significantly affect a child's quality of life.?However, the LAMP study demonstrated that low dose atropine is effective without any impace on quality of life.?The only draw back to low dose atropine as an method of myopia management is a significant rebound effect as compared to optical interventions, which has been demonstrated in several studies.?
Implementation:?Low dose atropine (0.01%) is approved as a method of myopia management by the Indian FDA, however, it is still prescribed off-label in most other countries.?It is also a prescription-only medication, which can prescribed by a medical practitioner only.?Therefore, Optometrists that wish to put their patients on low dose atropine would have to do it in co-management with an ophthalmologist.
Optical Interventions
Principle:?Early researchers in the contact lens field believed that myopic progression occurred due to corneal steepening during development and there were a few publications that loosely claimed rigid lenses could slow down the progression of myopia, although this was probably found in cases where the cornea was flattened due to the rigid lens.?Modern rigid lens designs tend not to cause corneal flattening or spectacle blue. This theory was disregarded when it was found that myopic progression is actually due to axial elongation that occurs during development, instead of emmetropization.?Recent literature revealed that the main cause of axial elongation is peripheral hyperopia, where when the myope is corrected with spectacles or regular contact lenses, while the central image is may be on the retina, the peripheral rays of light focus behind the retina, causing peripheral hyperopia.
Peripheral form deprivation due to peripheral hyperopia, stimulates elongation of the axial length. This was demonstrated in primates, where once the peripheral hyperopia was eliminated, the eye became emmetropic, even in cases where the fovea was ablated.?This indicates the magnitude of the role of peripheral hyperopia in myopic progression and based on this evidence, one could conclude that eliminating peripheral hyperopia may slow down the progression of myopia.?
Efficacy:?Optical interventions include Orthokeratology or Corneal Reshaping contact lenses, centre distance multifocal and extended depth of focus (EDOF) soft contact lenses and, more recently, specially designed spectacle lenses for myopia management.?There is enough literature to provide strong evidence demonstrating that?Orthokeratology and multifocal / EDOF soft contact lenses result in approximately 50% reduction of myopia progression.?As far as spectacle lenses are concerned, the literature is limited, although initial reports are very promising, demonstrating approximately 65% control of axial elongation in the duration of the studies, however further publications will provide a better idea of control over a longer period of time.?The two main designs that are being researched extensively are Highly Aspheric Lenslet Target (H.A.L.T) and Defocus Incorporated Multiple Segments (DIMS).
Safety:?The safety of contact lens wear in young children is frequently questioned by practitioners. Modern rigid lens materials providing excellent oxygen permeability allow safe overnight wear of contact lenses, without virtually no incidence of hypoxia related complications. Studies have shown that the incidence of microbial keratitis was most common in East Asian countries, where Pseudamonas and Acanthamoeba were the primary micro-organisms causing the infections. It was concluded that the reasons behind these incidences included poor adherence to care regimes, as well as use to tap water to rinse the lenses. Similarly, when it comes to soft contact lenses, typically, daily replacement lenses would be considered the safest as compared to a daily reusable lens, however for any contact lens wearer, child, teenager or adult, a combination of proper instruction from the eye care practitioner as well as strict adherence to the prescribed care regimen and regular follow up appointments minimise the risk of complications.
Implementation:?Spectacles are the least invasive method for myopia management, however, correct myopia protocols must be followed for all optical interventions for myopia.?Peripheral defocus soft contact lenses as well as orthokeratology require a level of training and expertise in contact lens fitting, but are excellent options for children who don't want to wear spectacles for any number of reasons including self esteem issues or sports and other leisure activities.?All optical myopia management strategies do come at a higher cost compared to conventional spectacles and contact lenses, which is something that must be considered while counselling the patient.
Environmental / Behavioural Interventions
As discussed in earlier, the amount of time spent out doors and working distances can considerably increase the risk of myopia progression.?Therefore counselling the parents and the children on behavioural and environmental interventions is essential.?These interventions include monitoring the working distance at which the child is carrying out near tasks and the amount of time spent at a stretch for near tasks.?The International Myopia Institute clinical management guidelines suggest that the working distance should not be less than 20cm and time spent should not exceed 45 minutes at stretch.?This does not mean that the child must not perform near tasks, but regular breaks are indicated, where the fixation is taken away from the near task.?Similarly the guidelines suggest that a minimum of 8 hours should be spent outside during daylight hours to reduce the risk of myopia progression.?The implementation of these guidelines should be the minimum responsibility of any eye care practitioner that has a myopic child under their care.
Myopia Management Protocol
Conclusion
Myopia management is on course to become a normal optometric practice, so it is important for all eye care professionals to familiarise themselves with all the interventions and correct protocols.?The Asira Digital Documentation platform allows detailed documentation templates for myopia management protocols.
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