The Influence of Light Exposure and Seasonal Changes on Short-Term and Longer-Term Changes in Axial Length of the Human Eye

Abstract

It is widely accepted that environmental factors play a significant role in regulating eye growth and myopia development. There is also considerable evidence that ambient light exposure is an important environmental risk factor associated with eye growth in children, however, the underlying mechanism remains unclear. Furthermore, animal studies have shown that diurnal variations in ocular components appear to be involved in the mechanisms controlling eye growth. Animal studies also suggest that altering light exposure disrupts normal diurnal variations and can lead to the development of refractive errors. Despite this evidence, the exact role of light exposure and ocular diurnal rhythms in the regulation of human eye growth, and the interaction between these factors is not well understood. Myopia development and progression have been widely documented in young adults and typically occurs due to axial elongation, but there has been limited research examining the potential impact of ambient light exposure upon eye growth and myopia development and progression in young adults.Therefore, this research examined the habitual light exposure patterns in a population of young adult emmetropes and progressing myopes using objective techniques, and assessed the influence of light exposure upon daily axial length variations and longitudinal axial eye growth in this population. The potential association between daily axial length fluctuations and longer-term changes in axial length was also explored.Since there is no consensus on the optimal sampling strategy required for capturing personal objective light exposure measurements, in the first study, we systematically examined the impact of different measurement durations and measurement frequencies upon objective light exposure measures, in order to determine the optimal sampling strategy to reliably capture habitual light exposure patterns of both children (Age: 11 to vi The influence of light exposure and seasons upon the axial length changes in humans 15 years) and young adults (Age: 18 to 30 years). Ambient light exposure data were obtained using a wrist-worn light sensor (Actiwatch 2), which was configured to measure instantaneous light levels every 30 seconds, 24 hours a day for a period of 14 consecutive days in children (n = 30) and young adults (n = 31). Daily time exposed to bright outdoor (>1000 lux) light levels was derived from the raw 14 days of data with 30 second sampling, and was subsequently derived from data re-sampled from 12, 10, 8, 6, 4 and 2 randomly selected measurement days using 1, 2, 3, 4, 5 and 10 minute sampling rates. Calculating daily outdoor light exposure time using a lower number of days and coarser sampling frequencies did not significantly alter the mean time spent in bright (outdoor) light. However, a significant increase in measurement variability occurred for outdoor light exposure derived from less than 8 days and from 3 minutes or coarser measurement frequencies in adults, and from less than 8 days and from 4 minutes or coarser...