How to identify and manage pre-myopes

Imagine this clinical picture: your patient is six years old and refraction is plano. Mum is -2.00D and Dad is -4.00D. Clearly this is not a normal refractive state for a six year old, and her parental history of myopia is concerning - this is a pre-myope. How can we consistently identify pre-myopes, explain the concern to parents, and how can we best manage them?

The International Myopia Institute - Defining and Classifying Myopia report¹ clearly defines the pre-myope:

This definition is made because while reducing progression of myopia is "a central goal of myopia research... preventing the onset of myopia is an even more valuable target." Identifying pre-myopia involves recognising a situation where a child has a non-myopic refraction, but a cluster of risk factors and/or "an observed pattern of eye growth" which indicates a high risk of progression to myopia."

There are four key principles for assessing risk of myopia onset:

• Family history – one myopic parent increases risk by three-fold, while two myopic parents doubles this risk again²
• Visual environment – less than 90 minutes a day spent outdoors increases risk, especially if combined with more than 3 hours a day spent on near work activities (outside of school time)³
• Binocular vision – Children with higher accommodative convergence (AC/A) ratios, typically seen with esophoria, have an increased risk of myopia development within one year of over 20 times.⁴ Accommodative lag may also be a risk factor but there is conjecture.⁵ Intermittent exotropia has also been associated with onset of myopia.⁶
• Current refraction – the most significant risk factor of this lot for future myopia is if a child exhibits 0.50D or less of manifest hyperopia at age 6-7. This risk is independent of family history and visual environment.

In addition to this, the fastest rate of refractive change in myopic children occurs in the year prior to onset,⁸ so the child who is less hyperopic than age normal should be closely monitored, especially if concurrent risk factors are evident.

How quickly should refraction change in emmetropization? The large scale Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study followed almost 5,000 children aged 6 to 14 for over a decade. Measured by cycloplegic autorefraction, emmetropia was defined as refractive error in the horizontal and vertical meridians between +1.00D and -0.25D. In their paper Normal Eye Growth in Emmetropic Schoolchildren,⁹ Zadnik et al demonstrated that the horizontal meridian changed from a mean of 0.64D at age 6 to 0.28D at age 14, and the vertical meridian from a mean of 0.58D at age 6 to 0.33D at age 14. Putting this into clinical terms:

After you have identified the pre-myope, the next challenge is explaining this to parents. The Myopia Profile Managing Myopia Guidelines Infographic, patient brochure and customizable insert (free to download) help to explain risk using a racing car analogy - each of the risk factors above 'fuels' the myopia car towards both onset and progression of myopia.

Perhaps the message on managing pre-myopia is even easier to communicate than for myopia management, when the child already needs vision correction. The key message to parents which will gain traction is probably the short-term view - a chance to delay or prevent their child's need for full time wear of glasses or contact lenses. A myopic parent especially will find this easy to understand.

Section 1 from The Myopia Profile Managing Myopia Guidelines Clinical Practice Infographic, from the 'Myopia Management in Practice' side which provides a reference guide for eye care professionals on myopia risk factors, prescribing decision trees, follow up schedules and gauging long term myopia management success. 

Managing the pre-myope is arguably more challenging than managing the myope - as the child does not yet require vision correction, this can take optical treatments off the table. There is also minimal research on interventions for pre-myopia, despite the International Myopia Institute stating that preventing myopia is an "even more valuable target"¹ for science and practice than reducing progression after onset.

Children whom spend less time outdoors, are far more likely to develop myopia.¹⁰ This is especially the case when two hours or less a day of outdoor time is combined with more than 3 hours of near work outside of schooltime.³

The magic amount of outdoor time is a little difficult to pin down, as research studies will variably define outdoor time by the mean reported time (with groups above and below average) or by the intervention (eg the 'recess outside classroom' program by Wu et al, in Taiwan, which amounted to an extra 40 minutes of outdoor time per day). Xiong et al attempted to find a dose-response effect in their 2017 meta-analysis¹⁰ and found that less than 13 hours a week (just under 2 hours a day) was associated with the highest odds ratio for incident myopia. On the basis of five studies investigating a dose response, they found that "an increase of 76 min/day, was needed to obtain a 50% reduction in incident myopia, while an increase of 1 hr/day or 7 hr/week will result in a 45% reduction in incident myopia compared with controls."

This is a simple, effective and achievable intervention which also may have positive effects on other factors of a child’s life such as reduction in body mass index (BMI), and less sedentary behaviours.¹¹ Don’t forget to encourage sun safety as well.

In 2010, Fang et al¹² retrospectively examined 50 children with an average age of around 8 years (range 6-12 years) who had less than +1.00D spherical equivalent refraction. Half of the children had received 0.025% atropine drops nightly for 12 months, while the other half hadn't and served as the control group. They found a significantly higher frequency of myopia onset in the control group (21% of the atropine vs 54% of the control), and a higher frequency of rapid progression (more than -0.50D shift in a year) with only 8% of the atropine group fitting this criteria while 58% of the control group did.

This is an indicative, but by no means a conclusive study. Children up to age 12 were included who arguably were not 'pre-myopes', and the control group was slightly older (mean age 8.2 years) compared to the 0.025% atropine treated group (mean age 7.6 years), meaning the former will be more likely to have slower refractive change. However it has led to the ATOM3 Clinical Trial, which has enrolled close to 600 participants in Singapore to be treated with either atropine 0.01% or a placebo for two years. It will investigate both the prevention of onset in pre-myopes and the control of myopia just after onset. The inclusion criteria are:

• Age 5 to 9 years
• One parent with myopia of at least 3D in one eye
• Spherical equivalent refraction +1.00D to +1.50D
• Astigmatism of no more than 1.50D.

Would you prescribe atropine for a pre-myopic child? Ultimately this comes down to collaborative communication with the parents to gain informed consent.

It would make logical sense that if a child presents with a binocular vision disorder linked to myopia onset, that managing the disorder may reduce risk. These specific disorders are:

• Higher accommodative convergence (AC/A) ratios, typically seen with esophoria, have an increased risk of myopia development within one year of over 20 times.⁴
• Accommodative lag may also be a risk factor but there is conjecture.⁵
• Intermittent exotropia (IXT) has also been associated with onset of myopia - 50% of children with  IXT are myopic by age 10, and 90% by age 20.⁶

It's important to note, though, that intervening in the above disorders for the purposes of delaying or preventing myopia onset is not evidence based - no study has been published to this effect. However treatment of these disorders as a principle of best practice optometric or orthoptic management is worthy, especially considering that binocular vision disorders can cause educational delays, asthenopia and headaches in children.¹³

There is no evidence that treating children classified as pre-myopic with myopia control contact lenses are effective in preventing the onset of myopia. Contact lenses, by nature, require significant parental intervention, cost and increase the risk of eye infection. However in parents whom perhaps have an older child already in contact lenses, potential strong enthusiasm to utilise an effective treatment is understandable. When faced with clear progressors (children who have rapidly changed from hyperopic to plano) with strong risk factors in the circumstances of a family keen for treatment, weighing the risk and benefits of contact lens treatment up with the patient and parent should be done clearly and carefully. For more information on paediatric contact lens wear, see our blog Contact Lens Safety in Kids.

Again, there is no evidence that myopia control spectacles stop the onset of myopia in the pre-myopic population. Many of these spectacle lenses are also in early release phases, clinical trial phases or only available in some areas (see Spectacles Lenses for Myopia Control Part 3 for the latest information). As this area of myopia research grows, this may potentially become a very low risk intervention option for some children. With safety being of minimal concern with a spectacle intervention, compliance in a perfectly sighted child may become more of the key management issue in attempts to delay myopia onset.

If the conversation has already occurred with parents on the identification and risks of pre-myopia, and outdoor activity and myopia control options discussed - and a child does progress to myopia, this makes subsequent myopia control intervention an easier decision for both practitioner and family.

By identifying pre-myopes as part of your routine clinical paediatric care, you will better integrate myopia control into your practice. Children can progress quickly, especially if you have already identified them as high risk, so ensuring that they are reviewed in at least six-monthly intervals important.

• Clinical case: Do you need to treat esophoria in an emmetropic patient?

• Clinical case: Managing a 5-year-old pre-myope

• Why outdoor time matters in myopia development