What Causes Shortsightedness (Myopia) to Get Worse?
There is no debate regarding the cause of myopia. We know that myopia increases because on an increase in the length of the eyeball. There is however growing evidence to support two theories to explain why the eye elongates (gets longer). These theories are:
- the accommodative lag theory
- the peripheral hyperopia theory
Recently, the peripheral hyperopia theory has received more attention and has been used to design lenses that aim to reduce the progression of myopia.
Progression of Myopia
In the UK there’s a 40% prevalence of myopia. Research shows that the prevalence of myopia has more than doubled since the 1960’s. Typically, childhood myopia in Caucasians and South Asians increases at a rate of approximately -0.50D per year until around the age of 15-16 years. This may not sound like much, but imagine if a child becomes myopic at 6 years of age and this myopia develops until they are 16 years old. That’s 10 years of -0.50D increase year on year resulting in a final level of -5.00D – that’s a level where glasses are required from morning till night.
Slowing Down Myopia – Therapies
A number of therapies are now recognised as being effective in slowing down shortsightedness. The current and most validated treatments (through independent published research) are based one specialized contact lenses, eye drops and lifestyle. In summary they are:
- Outdoor activity – at two hours of outdoor activity has been associated with reduced myopia progression.
- Orthokeratology – where a specialised lens is worn overnight only to improve vision so glasses or regular contact lenses are not required during the day.
- Specific multifocal contact lenses
- Low dosage atropine – this medication in dosages of 1/100th of the conventional dosage, has been shown to be effective in reducing the progression of myopia. However, this medication has not yet been officially licensed for use for myopia control in the UK.
How Effective are Therapies?
Myopia progression therapy achieves 30-59% reduction in myopia progression. Assuming there is a 50% reduction in myopia progression per year it’s easy to see that for effective limitation of myopia progression, treatment should start early and continue until the age of 16.
So, if we start treatment at 6 until 16 we theoretically limit myopia to only -2.50 compared to -5.00 if treatment was not offered.