The effect of time outdoors during daylight on spherical equivalent refraction and axial length in young Pakistani myopes: A Hospital-based case control study

Abstract

Objectives: This case-control study was carried out at a tertiary eye care hospital in Rawalpindi, Pakistan. The objective was to ascertain risk factors of myopia with emphasis on the effect of time outdoors in daylight hours, which seems to be protective according to the literature on western populations. Methods: This was a case-control study carried out at a tertiary eye care hospital in Rawalpindi, Pakistan. Data were collected using an adapted questionnaire, from the Aga Khan sun exposure and the Sujiatun Eye study questionnaires. Refractive power and axial lengths (Axl) were measured and compared with the many factors that are theorized to be associated with myopia. Individuals with a history of trauma, systemic diseases, surgeries, or other interventions, amblyopia, hyperopia, and high myopia were excluded. Results: Our results are in line with the trend that axial length is inversely associated with time outdoors in sunlight, which may be more important for females according to our sample. The correlation between time outdoors and axial lengths in summers and winters are (Pearson’s r = - 0.203, p=0.041) and (Pearson’s r = - 0.256, p = 0.01) respectively. Similarly, near-work and outdoor physical activities were not associated with a myopic spherical equivalent refraction. Conclusion: The low incidence of myopia in this age group as ascertained by a previous regional study, might explain why the effect observed in our sample is small, but axial lengths were used in the analysis which is perhaps more accurate in sunlight studies. Further studies using a larger sample, and objective methods of sun exposure are warranted. Keywords: Myopia, Time outdoors, Sunlight exposure