Mike: Hello, I'm Mike Clarke, podcast editor for the Cochrane Library. In some areas of health and social care, the evidence from individual randomised trials answering questions about single interventions makes it difficult to choose between the interventions. Network meta-analyses can help with this by bringing all the evidence together in one place and, in February 2023, Cochrane Eyes and Vision published one such review, looking at the control of myopia in children. Here's lead author, John Lawrenson from City University of London in the UK, to tell us more.

John: Myopia (commonly referred to as 'short-sightedness') is an eye condition in which those affected struggle to see clearly objects that are far away, while objects that are near remain clear. It's very common worldwide, with more than half the children in China and South-East Asia affected by it. Short-sightedness may impair many aspects of life, including education and work, and people with myopia have longer eyes, which means that the retina is stretched, increasing the risk of sight-threatening eye diseases such as glaucoma, maculopathy and retinal detachment later in life.
Although conventional eyeglasses or contact lenses can correct short sight, they do not slow its progression. Instead, other treatments might be used to try slow progression and these need to be given in childhood, when myopia progresses most quickly. These include special glasses and contact lenses with more than one focus in the lens. Other specialised contact lenses, called orthokeratology, aim to temporarily change the shape of the eye surface and are worn during sleep and removed during the day. But additional expertise is needed to fit these special lenses and they may not be as widely available as other treatments. Pharmacological interventions that involve the use of anti-muscarinic eye drops such as atropine, which act on the eyes focussing system and slow the rate of eye growth are also becoming more common.
In our Cochrane living review and network meta-analysis we aim to find out whether medications used as eye drops, and special lenses in eyeglasses or contact lenses, can slow the progression of myopia, as well as slowing the elongation of the eyeball in children. We also document the risk of unwanted effects of such interventions.
The February 2023 review includes 64 studies that randomised more than 11,000 children, aged 4 to 18 years and followed them for one to three years but with most of the studies only following the children for two years or less. Sixty percent of studies were conducted in China or other Asian countries and 20% in North America. Most of the studies compared myopia control interventions to a control group (either conventional glasses or contact lenses in the case of optical interventions or a placebo for pharmacological interventions) but we also looked at studies comparing different interventions against each other.
We found some promising results. These include that higher doses of atropine may reduce the progression of myopia and, based on short-term studies, orthokeratology seems to be the most effective of the optical treatments in slowing elongation of the eyeball. However, these lenses were often difficult to tolerate, with more than half of children not completing the treatment in some studies. Other more widely available types of contact lenses, known as multifocal contact lenses, may also reduce the progression of myopia, but, again, we remain uncertain about their beneficial effects.
Unwanted effects were not consistently reported. Eye discomfort in bright light and blurred near vision were the most common treatment-related unwanted effects in studies using atropine, with lower doses of atropine appearing to have fewer unwanted effects. Although studies that tested contact lenses did not report any serious unwanted effects, it is unclear what the true rate of unwanted effects would be for children outside a research study or when wearing contact lenses for longer periods.
The main limitation was that most of the evidence came from studies conducted in ways that may have introduced errors into their results, and potential unwanted effects were not well reported. Furthermore, because of the relatively short follow-up in most of the studies, there is insufficient evidence on whether incremental benefits are found over the years and whether the effects are sustained. However, because we are maintaining this review as a living systematic review, we will continue to incorporate new evidence as it becomes available.

Mike: If you'd like to read the current version of John's review, and future updates as new evidence is added, go to Cochrane Library dot com and search 'myopia control in children' for a link to it.