By Weizhong Lan, MD, PhD
Dec. 3, 2019
It is well understood that myopia commonly onsets in early childhood and continues to progress until late teenage years or early adulthood. The primary structural change in myopia is axial elongation beyond the intended eye length. As a result of the longer than normal eye length, the eye is at risk of developing complications such as retinal break and detachment, myopia maculopathy, choroidal neovascularization and glaucoma, especially in later life and the risk increases exponentially with the degree of myopia.[1, 2] Therefore, a key goal for myopia control is to control or slow progression to reduce the risk of high myopia.
In a myopic eye, there is good correlation between axial length and the degree of myopia. Therefore, both are good indicators in assessing the rate of progression of myopia. It is now well understood that myopia progression is faster in younger children and slows with age. The younger the age of onset of myopia, the greater the risk. In addition, ethnicity, parental myopia, and schooling are factors that were found to influence progression.
How to identify a fast progressing myope? Based on established risk factors, a child of Asian ethnicity, young age at presentation, risk factors related to parental myopia and near work, and a faster progression in the preceding months may be expected to progress faster. Furthermore, meta-analysis of eyes wearing single vision spectacles has found that the Asian eye progresses faster at an average of -0.82D for a child of 9.3 years of age, and in comparison, a Caucasian progresses at -0.55D. Thus an annual progression of about 0.75D or higher can be considered to be fast progression. Beyond that it is difficult to predict the progression rate for an individual eye with some certainty. Calculators such as the BHVI calculator may help understand the rate of progression based on age and ethnicity as these were derived from a meta-analysis of progression rates in spectacle treatments across Asian and Caucasian eyes.
How to manage a fast-progressing myope? The goal of the treatment is to slow or control the progression of myopia and thereby reduce the burden of frequent change of corrective/treatment devices that restore sight as well as to reduce the risk of future complications. A clear treatment plan is necessary that takes into consideration: a) myopia control strategy, b) a follow-up schedule to monitor progress, and c) instrumentation to monitor progression is an absolute must. Furthermore, communicating to the parents and/or careers that whilst the goal is to control myopia, there still will be continuing progression is important. Additionally, although the goal of the treatment is to slow/reduce progression, considerations need to be given to factors such as seasonal variation that may influence progression.
There are now available several spectacles, contact lenses, and pharmacological-based therapies that can slow myopia. In young children, for example, less than 6 years of age, application of a contact lens-based approach may pose issues to due safety and hygiene, and therefore, a spectacle based or pharmacological approach may be the default go-to option. Several spectacle based approaches based on progressive addition design, peripheral defocus modifying design, and prismatic bifocal design are available, and more recently, a lens design with multiple segments has shown promising results. Of the pharmacological approaches, Atropine, a muscarinic antagonist is the most widely used and found to be effective at concentrations of 0.05% and above. In older children, either soft contact lenses or orthokeratology are suitable options and may be combined with pharmacological approaches if needed.
At the follow-up visits, it is important to evaluate progression using same procedures as used at the baseline visit. Utilizing procedures/techniques that provide greater accuracy and precision in recording progression is also important. For example, a cycloplegic autorefraction or an axial length measurement is more precise than non-cycloplegic or subject refraction. Additionally, over the course of managing the individual, utilizing the same measurement technique or procedure to evaluate and track the individual’s progress is important. If the progression continues at the same pace or is faster than age-related norms, it would be advisable to review patient history, compliance, and seasonal effects, etc. prior to changing the management approach. For example, a pharmacological approach may be more prone to non-compliance as with a spectacle based approach, not using the device would result in poor vision. Also, if a child were introduced to a treatment plan in summer then accounting for an increased progression in winter months would be prudent. If it is recognized that the child is continuing to progress despite these factors, then the practitioner may need to consider switching approaches or consider combination therapies. For example, the combination of OK lens and low dose atropine was observed to produce enhanced efficacy. certain interventions may reduce over time, it is advisable to actively monitor the progression rate (at least on an annual basis).
In summary, the key point to managing myopia is to prevent it from developing to a high degree and therefore avoid relevant irreversible ocular visual impairment. Although there is no single solution to stop myopia progression, it is possible and manageable to slow down the progression rate so that myopia would end within a relatively safe degree.
Weizhong Lan, MD, PhD, Aier School of Ophthalmology, Central South University, China, is a visiting scientist with the Brien Holden Vision Institute.
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