br Environmental factors While we wait

Environmental factors
While we wait for more evidence for genetic determination of refractive error there does exist evidence pointing to environmental risk factors. The increasing prevalence of myopia and high myopia which at times has rapidly changed in Taiwan, Singapore, Hong Kong, Scandinavia, and the United States has been pointed out as likely being environmental. In can be difficult to compare prevalence studies if the protocol for sampling, refraction and use of cycloplegia is not standardized. Starting with a year 2000 study there have been buy dhpg studies in Chile, China, Nepal, Urban India, Rural India, South Africa, and Australia using a common or comparable protocol. This common protocol was further advanced in The Sydney Myopia Study which had a stratified random cluster sample a group of children aged 6 and a group aged 12, with a three year interval for reexamination. Data on eye structure and changes over time in this study include using Cyclopentolate use with auto refraction, noncontact biometry including optical coherence tomography. By also gathering data from the parents of the study population the study aimed to assess interactions between genetic and environmental risk factors.
Urbanization and educational attainment also has some contribution toward myopia development but only explains a small proportion of the variance seen. Near work has been identified as a risk factor but with a weak association and difficult to quantify.
Recently data have shown a protective effect of the time spent outdoors in 6–7year old children. This outdoor protective effect was also reported in 12year old Sydney children.(Rose et al., 2008b) The time outdoor protective effect has been reported in the United States, in Turkey, and in Jordan.(Khader et al., 2006) The Orinda longitudinal study found this protective difference precedes the onset of myopia. The reduction in the probability of developing myopia by eighth grade if a child had two myopic parents went from 0.60 if the outdoor time in the third grade was low (0–5h per week) to 0.20 if the outdoor time is high (>14h per week). Statisticians have modeled risk factors that include age, gender, ethnicity, school, IQ level, number of books read per week, height, parental myopia and adding time spent outdoors significantly improves the fit of the model.
To help measure the relative roles of the environment and genes it is valuable to examine the prevalence of similar ethnicity in a population that migrates to a different environment. This was done in comparing the prevalence and risk factors in 6 and 7year old children of Chinese ethnicity in Sydney and Singapore. The prevalence of myopia in the Chinese children was 3.3% in Sydney and 29.1% in Singapore yet the children in Sydney read significantly more books and had more total time in near activities. The most significant factor between the two sites was much more time on outdoor activities in Sydney. Measuring the prevalence rates in Caucasian and Chinese students in local and international schools in Hong Kong found both an effect of the different genetic background and an effect of the Hong Kong environment. Indians show a very low prevalence of myopia in India, however, the prevalence of myopia in Indians in Singapore is high. Park and Congdon argue that many of the prevalence studies in the literature have “significant shortcomings” chiefly due to lack of longitudinal data. Morgan and Rose feel there is enough environmental evidence that in high pressure environments with intensive mass-education systems in highly urbanized environments, almost everyone could become myopic.

Interventions to control juvenile myopia progression have included pharmaceutical agents, bifocal and Progressive lens glasses, and rigid gas permeable contact lenses. In a review of myopia trials to retard myopia progression in 2002 it was felt there was insufficient evidence to support any interventions.