Myopia is now the most common type of refractive error and one of the leading causes of functional blindness in the world.[1] Uncorrected myopia as low as −1.50 D will result in moderate vision impairment, and uncorrected myopia of −4.00 D is sufficient to be classified as blindness.[2]
Studies indicate that the prevalence rates of myopia in most parts of the world are rising. The global prevalence of myopia is expected to increase from 27% of the world's population in 2010 to 52% by 2050. In raw numbers, this would correspond to a 2.6-fold increase in the number of people with myopia.[3] A study conducted between June and December 2003 by the Ministry of Health, Sultanate of Oman, showed the prevalence of myopia to be 4.1% (95% confidence interval 4.06-4.18) among Omani school children.[4]
Myopia is believed to result from the interplay of genetic as well as environmental factors. Ocular growth may be largely regulated by local ocular mechanisms. Studies on retinoscleral signaling cascades have linked the retina, the presumed source of ocular growth signals, to the choroid and sclera, whose growth and remodeling ultimately determine the physical dimensions of the vitreous chamber and the location of the retina.[5]
The socioeconomic burden of uncorrected myopia has been estimated to result in a global loss of productivity of (US$ 202 billion), which will also increase if there is a significant increase in uncorrected myopia.[6]
The impact of myopia is not only financial but also affects quality of life and personal development. A study of Singaporean adolescents found that those with vision impairment had statistically significantly lower scores for total quality of life (P = 0.03), psychosocial functioning (P = 0.03), and school functioning (P = 0.02).[7] The increase in the prevalence of high myopia will lead to an increase in blindness and permanent vision impairment from pathological myopia, leading in turn to increased pressure on ophthalmological and low-vision services.
Due to accumulating evidence of an epidemic of myopia throughout the world with the associated high risk of sight-threatening complications (including myopic maculopathy, retinal detachment, choroidal neovascularization, cataract, and glaucoma) and a high socioeconomic burden, research scientists have studied methods to reduce myopia progression.
Various methods to control myopia progression, including undercorrecting myopia, bifocal or multifocal spectacles, orthokeratology (rigid gas permeable) contact lenses, and topical pharmaceutical agents,[8] have yielded disappointing results or positive results of marginal clinical significance. Topical atropine, however, has been shown to have a clinically significant effect. Atropine eye drops are antimuscarinics that nonselectively block the muscarinic receptors from being stimulated by acetylcholine. These receptors are found in the central nervous system and in the human ciliary muscle, retina, and sclera. There is now evidence that acetylcholine has a substantial role in eye growth regulation.[9]
Atropine in the Treatment of Myopia studies (ATOM 1 and 2) were randomized, double-masked, placebo-controlled trials each involving 400 Singapore children between the ages of 6 and 12 years. The ATOM 1 study reported that instillation of 1% atropine eye drops nightly in one eye over a 2-year period was well tolerated and effective in slowing the progression of low and moderate myopia by 77% and reducing the increase in axial length (mean axial length increase of 0.39 mm in controls versus no growth in atropine-treated eyes). The ATOM 2 study demonstrated a dose-related response with 0.5%, 0.1%, and 0.01% atropine slowing myopia progression by an estimated 75%, 70%, and 60%, respectively, over 2 years. However, when atropine was stopped, there was an inverse increase in myopia, with rebound being greater in children previously on higher doses. This resulted in myopia progression being significantly lower in children previously assigned to the 0.01% group at 36 months compared with that in the 0.1% and 0.5% groups. Use of atropine 0.01% offered the most desirable risk-benefit ratio, with no clinically significant visual side effects observed with higher doses.[9,10] The exact mechanism by which atropine 0.01% slows down myopia progression is unclear.
To date, similar studies have not been conducted in the Middle East and Gulf region, and the response of this population to atropine treatment needs to be explored.
References
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