The "epidemic"of myopia (short sight)
Can myopia be slowed down?
Myopia is increasing world-wide at an alarming rate. In Asia, the increase is believed to be 70–87% whilst in America and Europe it is between 20–50%. Not only that, but children are becoming myopic much earlier in life.
This is a real problem because higher levels of myopia is associated with increasing the risk factor for several eye problems including glaucoma, cataract, retinal detachment, and myopic maculopathy (like macular degeneration but at an earlier age) caused by the elongation of the eye in myopia which stretches the retina and makes it thin and liable to break and tear.
Even slightly short sighted people have a greater lifelong likelihood of eye disease than non-myopes . The higher the myopia, the higher the risk becomes.
Myopes between -3.00 and -5.75D have 3-fold increase in the risk of retinal detachment compared to non-myopic children. For myopes over -6.00D the relative risk is nearly 22 times as great.
Fortunately, there are now several evidence-based approaches have been shown to potentially slow myopia progression. Non drug approaches include the use of dual focus contact lenses, varifocal spectacles lenses and Ortho-k contact lenses.
Predictive calculators of myopia exist in the public domain (www.myopiacare.org) which can identify individuals ‘at risk’ of becoming myopic based on a number of predictive indices, including the history of parental myopia, sibling refractive error, ethnicity, age of onset of myopia and lifestyle parameters.
Strong evidence exists that spending time outdoors can protect against the onset of myopia and possibly reduce the final level of adult myopia. When children spend more than two hours per day outdoors the risk of myopia is reduced, even when they have two myopic parents and continue to perform near work.
The total time spent outdoors appears to be the important factor. One researcher reported that that the incidence of new cases of myopia over one year was approximately halved, when the time spent outdoors was increased by an additional 80 minutes per day. The rate of progression of myopia in children who spent additional time outdoors was also significantly reduced.
The ideal of 2 hours of sunlight a day may not be possible throughout all seasons, but a pragmatic approach to increase outdoor activity by as little as 40 minutes might significantly delay onset of myopia. It would seem that simple exposure to sunlight, potentially involving the production of Vitamin D offers some protective mechanism.
It was once thought that under-correcting myopia would slow its progression. However, many studies have now shown that under-correction actually speeds up progression. It is therefore important to fully and accurately correct myopic children and to see them regularly.
However, it is thought that standard single focus spectacles can themselves promote myopic elongation of the eye. Existing spectacle lens designs, such as large segment bifocals and progressive addition lenses designed to correct presbyopia (near focus problems of older people) have been shown to have a very small effect on myopia progression.
Research indicates that some existing soft multifocal contact lenses with a centre-distance portion, resulted in a 50% reduction in the progression of myopia. A study using a ‘dual focus’ daily disposable contact lens, not yet commercially available in the UK, has released very favourable interim results showing a better-than 50% reduction whist having good acceptance in terms of visual comfort and clarity.
Another useful option that has shown good results, with one study showing a reduction in myopia progression of 57%, is the technique known as orthokeratology (often abbreviated to Ortho-k). These are rigid contact lenses and are worn over night and removed in the morning a technique which has earned the lenses the nickname ‘optical retainers’. The overnight corneal re-shaping reduces central corneal curvature. This temporary flattening of the central cornea and mid-peripheral steepening reduces myopia and the vision correction remains for the next day and sometimes longer. Ortho-K has few clinically significant side effects although, as with other contact lenses worn overnight, there is a slightly greater risk of eye infections. Children wearing contact lenses have been shown to have similar risks to adults wearing the same lenses but this increased risk should be balanced against the benefits of reducing myopia.
Several studies have shown that fitting ortho-k lenses can slow the progression of myopia in school age children but the correction of myopia above -4.50D or significant astigmatism can be difficult with ortho-k. (although it is possible to deal with up to -6.00). People thinking about this option should therefore consider starting before they get to this level of short sight.
The effect of treatment is best in younger people. Most clinicians advocate close monitoring and fitting upon the first signs of myopia because under-correction has been shown to encourage progression. It is also possible to predict emerging myopia based on parental myopia, sibling myopia, lifestyle and other factors before the patient actually becomes myopic .
The decision to commence contact lens fitting in very young children depends on the maturity of the child, their ability to handle lenses and the level of parent support. Handling lenses is rarely a barrier to most children and as we are see more and more children becoming myopic at a younger age it is not uncommon to fit children as young as 8 with contact lenses.
The most effective time for starting myopia control has been shown to be for children under 12 years of age. Treatment should continue until the risk of progression has stopped. We are now seeing myopia progression through into young adulthood, especially when studying or near task demands are high. This means that more myopes are reaching greater levels of myopia than was seen just a few decades ago as the progression continues for a longer period.
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