UC Berkeley

Myopia, or nearsightedness, is a form of visual impairment in which distant objects appear blurry due to excessive axial eye growth that is mismatched to the eye's refractive power. This condition, though treatable with spectacles, contact lenses, or refractive surgery, continues to increase in prevalence, particularly in some Asian countries, where up to 80-90% of young people and students are myopic. High myopia (< -6.00 D) is associated with greater risk of glaucoma, retinal detachment, and other blinding complications.

Myopia is a complex disease with both genetic and environmental components. Rising myopia prevalence rates have mirrored lifestyle shifts that include reduced outdoor and light exposure. The directionality and impact of environmental risk factors, particularly light exposure, on myopia, continue to be poorly understood, partly due to the lack of in vivo and realtime instruments for measuring these effects. This dissertation examines the role of environmental risk factors in myopia, and introduces two new methods for quantitatively studying light and nearwork in humans.

Evidence from animal studies suggests short bursts of bright light may be sufficient to retard myopic eye growth. Recent questionnaire-based studies have found increased exposure to sunlight or outdoor environments to be correlated with reduced myopia in children. We supplemented the questionnaire approach with objectively gathered data from light sensors, and compared the accuracy of the two approaches. Maximum intensity, cumulative light exposure, frequency of intensity change, or time spent in bright light were not correlated with refractive error. Subjects overestimated time spent outdoors, and these estimates were in poor agreement with time reported by the sensor data. This is the first multi-season study to use both the questionnaire and light sensor methods coupled with local weather data to investigate light and outdoor effects in myopia.

The duration and degree of another myopia risk factor, nearwork, are typically estimated retrospectively through questionnaires that assess reading, computer use, and other visual behaviors. There are, however, no comprehensive methods of measuring working or fixation distance in realtime during natural tasks. Here we present a new approach for studying the dioptric environment in humans. A head-mounted eye tracking device was adapted to be fully mobile for the realtime measurement of eye movements, including convergence. This device was validated in a small sample of young adults. We conducted exploratory analyses of possible task-related trends in fixational behavior, fixation distance, horizontal eye movements, blinks, and saccades. We found large differences in some of these metrics between reading and walking tasks; these task-dependent changes in visual behavior may underlie the nearwork effect in myopia progression.

Light sensing and eye tracking are new techniques for quantifying behaviors that are thought to be involved in myopia development. Unlike questionnaires, these methods provide realtime, unbiased data at the temporal resolution that is relevant to refractive error development. Environmental pressures may be a tipping point toward pathological eye growth for genetically susceptible individuals, and further work in this vein could lead to simple behavioral interventions to curb myopia progression.