City Research Online

Abstract

Exposure to bright outdoor light is shown to be associated with preventing or delaying the onset of myopia, and slowing its progression. Young myopes have been shown to spend lesser time outdoors and are exposed to lower illuminance levels, compared to their non-myopic peers. However, this evidence was obtained from Caucasian or East Asian populations only. Considering the diversities in geography, environment, culture, socio-economic status, education and lifestyle of children in India compared to other ethnicities, exploring light exposure profiles in this population could add new insights into the field of myopia. The overarching aim of this PhD is to investigate the interactive role of light exposure, and general ergonomics of classrooms on myopia in Indian school-aged children.

The work described in this thesis is comprised of six objectives. The thesis consists of a combination of evidence synthesis using a systematic review methodology and primary research to explore aspects of ambient light exposure on myopia. Outdoor and classroom light exposure levels were determined and the relationship between individual light exposure and myopia progression was investigated using a wearable light tracker that was developed and validated specifically for this study.

An overview of systematic reviews concluded that exposure to bright outdoor light during early childhood could reduce incident myopia by 24-46%, however, its effect on myopia progression was not clinically significant. A Cochrane systematic review of interventions for myopia control did not identify any eligible trial that investigated efficacy of time spent outdoors on childhood myopia progression. A cost-effective, accurate, durable, and safe wearable light tracker (named as MyLyt) was developed to track light exposure patterns for extensive research and clinical purpose. The MyLyt trackers measured a daily illuminance exposure level of 807 (IQR 507,1079) lux/day, and 46 (IQR 30,64) min/day time spent in an outdoor light condition in Indian school children. Importantly, non-myopes were exposed to significantly higher daily illuminance exposure levels and spent more time outdoors than myopes during a typical school day. However, the annual change in axial length was found to be similar between participants, irrespective of their refractive status. The findings highlight that the ambient light exposure parameters estimated at specific time points in a year did not show its association or role in altering axial length over a period of one year in Indian school children.

Investigation of the spectral composition of ambient light in different indoor and outdoor locations revealed that irrespective of location, time of day, day, and season, the spectral power distribution of ambient light was always higher (on average 157x) in the outdoor locations compared to indoors. Further analyses indicated that the absolute spectral power of short (380-500 nm), middle (505-565 nm), and long (625-780 nm) wavelengths significantly varied between indoor and outdoor locations, but relative percentage composition was similar. Exploration of general ergonomics of school classrooms in India revealed that the overall median illuminance level inside a classroom was 271 (141,431) lux, which varied with the type of schools categorised based on location (rural vs urban schools) and funding source (government vs privately funded).

The results of this work have generated new evidence that led to the advancement of science in the field of light exposure and myopia. It has also laid a foundation to further explore and investigate light-based myopia control interventions.

Publication Type:	Thesis (Doctoral)
Subjects:	R Medicine > RE Ophthalmology R Medicine > RJ Pediatrics > RJ101 Child Health. Child health services
Departments:	School of Health & Psychological Sciences > Optometry & Visual Sciences School of Health & Psychological Sciences > School of Health & Psychological Sciences Doctoral Theses Doctoral Theses

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