– Myopia –
Myopia Epidemic
Myopia (short-sightedness) has become increasingly prevalent both around the globe and here in Australia. Global statistics show that currently 30% of the world’s population is myopic, and future projections estimate this will escalate to a staggering 50% or 5 billion people by 20501. These trends have been seen recently in Australia as well, with a recent study in Sydney finding that 31% of 17-year-old children were myopic, a number that almost double what was found previously2. This worldwide increase in myopia is likely to lead to a future burden on public health programs and has been flagged by the World Health Organisation as an upcoming global issue. This is because higher levels of myopia can lead to eye health complications (such as myopic macula degeneration, retinal detachment and glaucoma) which are all associated with permanent vision loss.
Myopia onset is typically seen in childhood or adolescence. Most concerningly, myopia can often first be seen in young children, where it tends to progress (i.e. the prescription will increase) very rapidly. The younger a child becomes myopic, the worse the future prescription: a child who requires their first myopic prescription before the age of 10 has the strongest progression, whilst a 15 year old child progresses at a much slower rate5.
New technology now lets us input a child’s current eye length (axial length), prescription, and their family history into a program that can predict how myopic a child will become. The younger a child starts developing myopia, the worse the predicted outcome. However, this can be significantly slowed by many myopia control interventions, all offered at the Myopia Clinic.
What Is Myopia?
Myopia is predominantly the result of an elongation of the eye, with longer eyeballs resulting in higher levels of short-sightedness. As the eyeball lengthens, the back of the eye is stretched and stressed, resulting in an increased risk of developing eye diseases such as cataract, glaucoma, choroidal retinal degeneration and retinal detachment later in life3. Currently studies suggest that with every 1 dioptre increase in myopia the risk of ocular disease increases by 67%, making myopia control extremely important, especially in young eyes4.
This is the primary reason why the Myopia Clinic exists: to develop a treatment plan for every child diagnosed with myopia to inhibit further growth of the eye and prevent the severity of future ocular health issues as a result.
Myopia risk analysis
Myopia onset for a child varies with age, gender, ethnicity and family history (that is whether either Mum or Dad or both also have myopia). How fast a child’s myopia will progress without intervention will also depend on a combination of these risk factors.
Factors that we know increase the risk of myopia development and progression are2
- Age: if the child becomes short-sighted at age 9 or younger, a much higher prescription will result without intervention
- Genetics: If one or both parents are myopic, it is much more likely their children will become myopic
- Ethnicity: children of east Asian decent are more likely to become myopic
- Gender: statistics females have a higher incidence of being short-sighted than their male counterparts
- Amount of myopia (how big the prescription is): if the myopic (short-sighted) prescription is higher than the age-based average, this increases risk of further progression (that is, higher prescriptions are harder to control and usually progress faster)
- Occupation: there is evidence to support that myopic progression is more rapid when more time is spent on reading/close activities and less time is spent on outdoor activities. The research is currently inconclusive as to whether this is related to the task (near versus distance focused activity) or the light levels (outdoor versus indoor light)
Good myopia management requires knowledge of these risk factors, the ability to measure them over time and the strategies to slow down the rate of progression.
Do Glasses Make Myopia Worse?
Our current understanding of the biological mechanisms behind myopia progression involve how light is focussed on both the central and peripheral retina. When you wear glasses for myopia, it focuses central light on the retina (giving nice clear distance vision), but the peripheral (the edges of the glasses) light is focused behind the retina. Research hypothesizes that the eyeball grows longer in order to focus this peripheral light. This then makes the prescription worse as a result.
All treatment options practiced in The Myopia Clinic are evidence based and are designed to focus peripheral (edge) light in front of the retina, slowing the growth of the eye.
Axial Length & myopia Progression
The length of the eyeball (or axial length) is the gold standard of monitoring myopia control. This is because the average eye length is approximately 23.14mm6. However, the average length of a highly myopic -6.00D eye is approximately 26mm long. Although the extra 3mm in length does not sound like much, the additional axial length is linked to a much higher risk of eye disease in the future. This is why measuring the length of the eye during the consultation is so important. This specialised piece of equipment (optical biometer) is something not all optometrists have but is essential for monitoring myopia progression correctly. It also helps determine which young myope is more at risk (ie already over 24mm) and can dictate the level of proactivity in the treatment plan that is required to slow progression.
References
1. Holden BA, Fricke TR, Wilson DA, Jong M, Naidoo KS, Sankaridurg P, Wong TY, Naduvilath TJ, Resnikoff S, Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050, Ophthalmology, May 2016 Volume 123, Issue 5, Pages 1036–1042.
2. Attebo K, Ivers RQ, Mitchell P. Refractive errors in an older population: the Blue Mountains Eye Study. Ophthalmology 1999;106:1066-72
3. Huang J, et al. (2016). Efficacy Comparison of 16 Interventions for Myopia Control in Children. Ophthalmology. 123(4): 697-708
4. Bullimore, M. Myopia control: why each dioptre matters. Contact lens and Ant Eye 42 (6)
5. Polling JR, Klaver C, Tideman JW. Myopia progression from wearing first glasses to adult age: the DREAM Study. British Journal of Ophthalmology Published Online First: 25 January 2021. doi: 10.1136/bjophthalmol-2020-316234
6. Hashemi, H., Khabazkhoob, M., Miraftab, M. et al. The distribution of axial length, anterior chamber depth, lens thickness, and vitreous chamber depth in an adult population of Shahroud, Iran. BMC Ophthalmol 12, 50 (2012). https://doi.org/10.1186/1471-2415-12-50
