Background: Myopia prevalence is rising around the world at a rate that cannot be explained by genetics alone therefore, environmental risk factors must have an influence. Accurate measurements of refractive error and potential risk factors are required to better understand the relationship between environment and refractive development such that evidence-based advice can be provided to patients and parents by eye care professionals. This thesis was designed to investigate some potentially modifiable risk factors for myopia in young UK children. Methods: One hundred children (aged 6-9) participated in cross-sectional evaluation of previously proposed environmental risk factors for myopia. Spherical equivalent refraction (SER) and axial length (AL) were determined by cycloplegic autorefraction and ocular biometry. Potential risk factors for myopia were measured using Actiwatch 2 and Clouclip devices. Screen time, sleep, physical activity, and parental myopia data were collected using questionnaires. 42 children were followed up 12-months after baseline and change in SER and AL measures examined. Correlations were explored between change in SER and AL and baseline environmental exposure profiles. Results and Conclusions: The data demonstrated that: • Compared with children classed as non-myopic (≥+0.75 D), pre-myopes/myopes (< +0.75) go to bed later and fall asleep faster (increasing their sleep efficiency), are exposed to higher illumination during sleep, and have poorer subjective sleep quality. Over 12-months, higher sleep efficiency and less wake after sleep onset were associated with faster axial elongation, whereas less time spent in mesopic light was associated with faster myopic progression. • Compared with children classed as non-myopic, pre-myopes/myopes spent significantly more time undertaking moderate-vigorous physical activity later in the day, potentially disrupting circadian rhythms. • More myopic SER's were significantly associated with increased time spent viewing at near on weekday mornings and increased time spent on intermediate viewing was significantly related to greater myopic shift over 12-months.• Using a phone/tablet for 1-2 hours/day, watching TV/video games 1-3 hours/day and a higher duration of near work all increased the likelihood of children demonstrating accelerated eye growth over a 12-month period. • Parents wishing to mitigate against myopia-promoting eye growth should encourage; less near work, less time on phones/tablets or watching TV/video games, less bright light and less physical activity in the evenings, earlier bedtimes and sleeping in darkness.