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?
What is pre-myopia?
The International Myopia Institute - Defining and Classifying Myopia report1 clearly defines the pre-myope:
Pre-myopia – a refractive state of an eye of ≤ 0.75 D and > 0.50 D 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.
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."
Identifying the pre-myope
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.7
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.
The most significant risk factor for future myopia is if a child is +0.50D or less at age 6-7, independent of all other factors. Also watch closely for the child who loses hyperopia quickly between visits, as the fastest refractive shift in myopes occurs in the year just prior to myopia onset.
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:
If your school aged, presumed emmetrope loses 0.50D or more of age-normal hyperopia in a year, you may be looking at a future myope.
Explaining pre-myopia to parents
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
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.
Pre-myopia interventions with direct research evidence
--> Increased outdoor time
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."
Research indicates we should aim to increase outdoor time to a total of around two hours per day, average, to have the greatest effect on delaying or preventing myopia onset.
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.
--> Low-concentration atropine
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.
Pre-myopia interventions without direct research evidence (but which may make logical sense)
--> Treating binocular vision disorders
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
--> Plano myopia control contact lenses
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.
--> Myopia control spectacles
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.
What to do next for the pre-myope
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.
- Flitcroft DI, He M, Jonas JB et al. IMI - Defining and Classifying Myopia: A Proposed Set of Standards for Clinical and Epidemiologic Studies. Invest Ophthalmol Vis Sci. 60, M20-M30, doi: https://doi.org/10.1167/iovs.18-25957 (2019).
- Jones LA, Sinnott LT, Mutti DO, Mitchell GL, Moeschberger ML, Zadnik K. Parental History of Myopia, Sports and Outdoor Activities, and Future Myopia. Invest Ophthalmol Vis Sci. 2007;48:3524-3532.
- Rose KA, Morgan IG, Ip J, Kifley A, Huynh S, Smith W, Mitchell P. Outdoor Activity Reduces the Prevalence of Myopia in Children. Ophthalmol. 2008;115:1279-1285.
- Mutti DO, Jones LA, Moeschberger ML, Zadnik K. AC/A Ratio, Age, and Refractive Error in Children. Invest Ophthalmol Vis Sci. 2000;41:2469-2478.
- Mutti DO, Mitchell GL, Hayes JR, Jones LA, Moeschberger ML, Cotter SA, Kleinstein RN, Manny RE, Twelker JD, Zadnik K, the CLEERE Study Group. Accommodative Lag before and after the Onset of Myopia. Invest Ophthalmol Vis Sci. 2006;47:837-846.
- Ekdawi NS, Nusz KJ, Diehl NN, Mohney BG. The development of myopia among children with intermittent exotropia. Am J Ophthalmol. 2010;149(3):503-507.
- Zadnik K, Sinnott LT, Cotter SA, Jones-Jordan LA, Kleinstein RN, Manny RE, Twelker JD, Mutti DO, Collaborative Longitudinal Evaluation of E, Refractive Error Study Group. Prediction of Juvenile-Onset Myopia. JAMA Ophthalmol. 2015;133:683-689.
- Mutti DO, Hayes JR, Mitchell GL, Jones LA, Moeschberger ML, Cotter SA, Kleinstein RN, Manny RE, Twelker JD, Zadnik K. Refractive error, axial length, and relative peripheral refractive error before and after the onset of myopia. Invest Ophthalmol Vis Sci. 2007;48:2510-2519.
- Zadnik K, Mutti DO, Mitchell GL, Jones LA, Burr D, Moeschberger ML. Normal eye growth in emmetropic schoolchildren. Optom Vis Sci. 2004 Nov;81(11):819-28. doi: 10.1097/01.opx.0000145028.53923.67.
- Xiong, S. et al. Time spent in outdoor activities in relation to myopia prevention and control: a meta-analysis and systematic review. Acta Ophthalmologica 95, 551-566, doi:10.1111/aos.13403 (2017).
- Centis, E. et al. A controlled, class-based multicomponent intervention to promote healthy lifestyle and to reduce the burden of childhood obesity. Pediatr Obes 7, 436-445, doi:10.1111/j.2047-6310.2012.00079.x (2012).
- Fang, P. C., Chung, M. Y., Yu, H. J. & Wu, P. C. Prevention of myopia onset with 0.025% atropine in premyopic children. J Ocular Pharm Ther 26, 341-345, doi:10.1089/jop.2009.0135 (2010).
- American Optometric Association. Care of the Patient with Accommodative and Vergence Dysfunction (St Louis, 2001). Accessed 19 October 2020.