Myopia (short-sightedness) is associated with an increased risk of permanent vision loss. A metabolite of caffeine called 7-methylxanthine, licensed in Denmark since 2009 as a treatment to reduce the rate of childhood myopia progression, is the only orally administered therapy available. In a new study, researchers from Trier Research Laboratories, Jinan University and Cardiff University assessed the rate of myopia progression in children taking 7-methylxanthine.
7-methylxanthine may slow the progression of myopia in children. Image credit: National Eye Institute.
“Myopia often starts at the age of 6-7 years and progresses until the age of 16-20 years,” said lead author Dr. Klaus Trier from Trier Research Laboratories and his colleagues.
“The excessive stretching and thinning of the retina, retinal pigment epithelium and choroid associated with myopia may lead to complications including retinal detachment, myopic macular degeneration and glaucoma.”
“Currently available pharmacological and optical intervention methods do not completely arrest myopia progression.”
“Caffeine has the status of ‘generally regarded as safe’ in the United States. It can, therefore, be added to dietary products and sold over the counter without restrictions,” they added.
“Theobromine, a first-order metabolite of caffeine, was previously used to treat asthma in children in doses of up to 3,000 mg per day.”
“The acute and chronic toxicity of 7-methylxanthine (7-MX) is several times lower than that of both caffeine and theobromine.”
7-MX has been used to treat childhood myopia in Denmark since 2009. But until now it has not been fully evaluated in long term studies, and Dr. Trier and co-authors wanted to find out how quickly myopia progresses in children taking 7-MX.
The researchers reviewed the medical records of 711 children (356 girls and 355 boys) treated for myopia at one eye clinic in Denmark between June 2000 and January 2021.
Comprehensive eye tests, including measurement of axial length, were carried out on the children.
And 624 of the children took 7-MX tablets up to 1,200 mg daily (average 470 mg) while 87 didn’t, for various reasons.
Their average age was 11 (range 7-15) when they started treatment, and their eye length and degree of myopia were tracked for an average of 3.5 years (range 11 months-9 years).
“Dioptres (D) are the units of measurement used to assess the extent of eye function,” the scientists said.
“The average degree of refractive error (short-sight) to begin with was −2.43 D, which increased by an average of 1.34 D during the monitoring period. -3.00 D is regarded as moderately severe myopia; -6 D or more is regarded as severe myopia.”
“Average axial length was 24.4 mm, to start with, increasing by an average of 0.21 mm/year.”
Treatment with 7-MX was associated with a slower rate of worsening myopia and axial elongation, with higher doses seemingly more effective.
Based on these data, the authors estimated that for a typical 7 year old with a refractive error of −2.53 D to start with, that child’s myopia would increase by −3.49 D over the next 6 years without treatment.
But with a daily dose of 1,000 mg of 7-MX, that same child’s myopia would increase by −2.65 D over the next 6 years.
Similarly, without treatment, axial length would increase by 1.80 mm over 6 the next years, whereas it would increase by 1.63 mm on a daily dose of 1,000 mg.
The team calculated that, on average, for an 11 year-old taking 1,000 mg 7-MX daily that child’s myopia would increase by −1.43 D over the next 6 years, compared with −2.27 D without treatment. And axial length would increase by 0.84 mm compared with 1.01 mm without treatment.
None of the children taking 7-MX reported any side effects during the monitoring period.
“Existing myopia control intervention methods are not fully effective in preventing children from progressing to high myopia, and 7-MX may become a valuable supplement if causality and efficacy can be confirmed in future randomised controlled trials,” the researchers said.
The results were published in the British Journal of Ophthalmology.
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K. Trier et al. Oral administration of caffeine metabolite 7-methylxanthine is associated with slowed myopia progression in Danish children. British Journal of Ophthalmology, published online August 22, 2022; doi: 10.1136/bjo-2021-320920
